Agricultural meteorology in relation to the use of pesticides in the U.S.A.

Agricultural Meteorology - Elsevier Publishing C o m p a n y , A m s t e r d a m - Printed in T h e N e t h e r l a n d s

Review A G R I C U L T U R A L METEOROLOGY IN RELATION TO THE USE OF PESTICIDES IN THE U.S.A. J. A. RILEY AND W. L. GILES

U.S. Weather Bureau, Memphis, Tenn. (U.S.A.) ; Mississippi State University, State College, Mississippi, Miss. (U.S.A.) (Received June 10, 1964)

SUMMARY

Agricultural meteorology is related to the use of pesticides in three broad areas: (1) weather affects the transportation of pesticides, (2) weather affects the transformation of pesticides, and (3) weather affects the pest and thus the need for a pesticide. In most control programs, drift is an important variable in achieving safe and efficient pesticide placement. Wind, air stability, the type of application equipment, and the formulation of the chemical influence drift. We found a great deal of useful drift research in the literature. It appears that a further need is for more widespread distribution of this information accompanied by a nation-wide system ot timely drift advisories for operational use of applicators. The physical processes involving the influence of weather on chemical transformation, degradation and removal are not as well understood as the processes involved in drift. Research is the big need in this area. Modification of the meteorological conditions of the pest microenvironment offers a real challenge. Agricultural meteorologists have been included on the team of agricultural research specialists and have made notable contributions to this effort for some crop pests. Further joint research along this line can give significant increases to agricultural efficiency and public safety by reducing the need for chemical pesticides.

PREFACE J. E. NEWMAN

Regional Editor of Agricultural Meteorology, Lafayette, Ind. ( U.S.A, )

This article reviews much of the current scientific literature on a rather controversial subject--that of extensive use of chemical pesticides in commercial agricultural production, particularly within the United States. The authors bring out some of the current philosophical thought on the subject. Also, the authors outline deficiencies Agr. Meteorol., 2 (1965) 225-245

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in existing scientific knowledge, as well as raise important questions which need immediate answers. Lastly. they suggest the pertinent areas of need for future scier~tific investigations.

INTRODUCTION The use of pesticides has become as large a management factor in agriculture as irrigation, fertilization, and other necessary cultural practices. In addition, the use of pesticides is often a more complex operation and has more far-reaching implications. Production of insecticides and fungicides in the United States totaled about 150,000 tons in 1941 and 200,000 tons in 1946. Weed killer chemicals became a large factor later and the combined production of insecticides, pesticides, and weed killers totaled about 320,000 tons in 1951, 370,000 tons in 1956, and 410,000 tons in 1961 (U.S. DEPARTMENT OF AGRICULTURE, 1963). Somewhat over one, third of the production is exported, but this leaves a large tonnage to be distributed in this country, and it increases every year.

PESTICIDELITERATURE The volume of published reports on pesticide research increased in proportion to the increased use of pesticides through 1960. Since then, however, the pesticide problem has evolved into a great national debate. The number of technical articles increased greatly, and the national press devoted much attention to the subject. This paper reviews a portion of the literature dealing with agricultural meteorology and its effect on the use of pesticides. Of the many recent articles devoted to broadseale implications of pesticides, the following excerpts from the Supplement to the January 1964 Issue of the American Journal of Public Health (COLE, I964; DARBY, 1964; HALLERY, 1964) are thought to synthesize current thinking. Even the article titles emphasize the undecided nature of the pesticide controversy. "Pesticides: A contribution to agriculture and nutrition", written by Dpa~BY (1964), states: "In 1940, it was estimated that the labor of one farmer produced food and fiber sufficient for about eleven persons; today, he provides enough for 26-29 individuals... A part of this revolution has been the intense, concentrated, scientific form of agricultural crop management. This makes for efficiency, but at the same time makes crop land more susceptible to disastrous losses due to unexpected or uncontrolled epidemics of plant diseases or invasion by uncontrolled animal pests.'" "Pesticides: The challenge, how do we meet it?", written by HALLFRY(1964), states: "What are pesticides doing to the atmosphere around us? .... I believe that the U.S. Public Health Service does not consider airborne pesticides a communityAgr. MeteoroL, 2 (1965) 225-245

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wide public health problem. Unlike other air pollutants, pesticides are formulated to settle rapidly and not to spread widely over a community." "Pesticides: A hazard to nature's equilibrium", written by COLE (1964), states: "Man is doing many things that thoughtful biologists find disturbing; the widespread use of pesticides is only one of these... Studies of the ecology of potential pest species and the species to be protected could pay big dividends. The casual exterminator would neither notice nor recognize the significance of the fact that in parts of California, while parasites fail to control the purple scale insect, 90~o of these pests are confined by micrometeorological conditions to the northern halves of the trees. Thus, there is present a chance for selective treatment to eliminate the bulk of the pest population with a minimum risk of destroying community diversity through broadcast exterminating procedures." The Fifth International Pesticide Congress, held in London (DIMOND et al., 1964), and the PRESIDENT'S SCIENCE ADVISORY COMMITTEE(1963) report, The Use of PesticMes, emphasize that more specific detailed data is the big need in pesticide research. The President's Science Advisory Committee included the following among its recommendations: "Amplification of research resources--only by stimulating training and basic investigation in the fields of toxicology and ecology are research needs likely to be met." Ecology and agricultural meteorology overlap in many areas, and further knowledge in these fields can contribute to pesticide research. EGLER (1964) in his thought-provoking essay, "Pesticides in our ecosystem", believes that ecology should include the study of an entire ecosystem. The "eco" should not mean environment of or something around something else, but should mean the totality of a site or habitat and everything in it. In meteorology, an individual low pressure system has been studied as a separate entity, but we now know that it is part of the general circulation and must be studied in this perspective. By analogy, pesticides cannot be separated from the environment but must be studied as part of a totality. Chemicals used to kill insects, spiders, mites, rodents, fungi and weeds are normally considered to be pesticides. Defoliants, dessicants, growth regulants, and fruit thinners are frequently classed in this group also. In its broadest sense, a pesticide is a chemical used to eliminate an unwanted living organism classified by the gross term "pest". Moisture, temperature, radiation, and air movement, as well as many subclassifications of these basic weather classes, affect most pests, their hosts, and the pesticides designed for pest control. At times, a single weather parameter may appear to be the controlling factor, but more often a complex of several elements is the determining factor. When explored in sufficient depth, most relationships between weather and the use of pesticides are found to be a complex concatenation involving weather, pest, host, and pesticide. There are many interrelationships. Rain is the most obvious weather element to affect the use of pesticides. A chemical that is immediately washed off the target does little good. It is uneconomical. It can produce undesirable side effects. Agr. Meteorol., 2 (1965)

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In non-irrigated areas, the role of pesticides in agricultural production bears an analogy to the role of"rainfall. Efficient production requires a good distribution o f bolh. Many areas have shown that rain is not required; only soil moisture. If lherc were areas free of pests, pesticides would not be required either. But, as far as we know, there are no areas free of the potential of rapid build-up of pests. Microweather conditions within protected areas permit pests to thrive in regions where macroweather conditions as reported by standard weather observing stations exceed critical pest survival thresholds. Indeed the pest problem is, in part, a result of the unnatural environment generated by homogeneous crop practices. Large areas of the same crop grouped closely together have provided ideal conditions for pest development. In this review we have found three primary relationships: (1) weather affects the transportation of pesticides, (2) weather affects the transformation of pesticides, and (3) weather affects the pest and thus the need for a pesticide.

P L A C E M E N T OF PESTICIDES

Efficient application of dusts, aerosols, sprays and granular forms of pesticides calls for a balance between two opposing objectives. The amount of chemical placed at desired locations should be the amount necessary to destroy the pest; the amount placed at undesired locations should be a minimum. The hazard to people, animals and plants demands that chemicals do not penetrate certain critical areas, The efficiency of agriculture requires that vahmble chemicals should not be wasted. Hazardous conditions resulting from undesirable placement of pesticides fall into two fairly well defined types: (1) eradication programs where chemicals are broadcast over a broad area (see section Eradication programs) and (2) local control programs where chemicals drift from the control area into an area not designed for control.

Pesticide drift California, Mississippi and Texas use over one-third of the nationally applied pesticides, and outstanding drift research has been done in these three states, In California, AKESSON and YATES (1964b) indicated three factors that must be considered in a drift study: (1) the type of distribution equipment and methods of use, (2) the physical form or formulation of the chemical used, and (3) the micro-meteorological conditions prevailing during the interval of discharge from the applicator until its deposition on the target.

Type of distribution equipment Applications by aircraft usually result in greater drift than applications from ground

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rigs. The generally accepted reason for this is that the chemical is mixed with a greater volume of air for possible drift from the treated area (A~oNYMOUS, 1962). Another factor is the effect of speed. A man flying an aircraft a few feet above a field is very busy. It is quite difficult to start and to stop the application at the proper instant and to locate the aircraft in the proper position required to place the pesticide in the precise spot it is needed. It is likely that large ground sprayers using high velocity blowers do produce a drift hazard equal to that of aircraft. AKESSO~and YATES(1964b) found that normally, however, there is more control over a ground rig, and the velocity with which the chemical is discharged is less. Aircraft do have many advantages over ground rigs and two of them are weather associated. No matter how thick the foliage has become because of excessive rain, or how muddy the soil, aircraft can deliver the pesticide. The release patterns from a fixed-wing plane and from a helicopter are similar. Chemicals are released downward, dispersed outward, drawn upward near the wing tip or the rotor tip, rotated in this zone, and then settle to the ground. The vortex system--the rotation at the wing tip or rotor tip is a basic function of both types of equipment. A strong central propeller wash develops with fixed-wing aircraft, and this has the undesirable feature of skewing the wake to one side of the aircraft's centerline. The helicopter pattern is generally better than the fixed-wing aircraft because this skewing is not a factor. In California, AKESSONand YATES(1964b) found that down-wash from the helicopter gives greater penetration of crop cover when hovering, but with forward speeds of 15-25 miles/h, this becomes insignificant. Usually the practical swath width is limited to the positions of the vortices, thus normal coverage is limited to the wing span or the width of the rotor. The Agricultural Engineering Department of Mississippi State University designed and tested a positive energy system to permit a greater degree of control over the ejected materials and to produce considerably greater swath widths. The usual venturi or ramair system gives a swath width of 30~,5 ft. Preliminary tests at Mississippi State University (ROBERTS and SMITH, 1963) showed that the positive energy system can produce a fairly uniform distribution over 80-100 ft. This system assures a wider dispersal of materials, but in doing so it probably increases the drift potential. A number of places are testing dispersal booms that are lowered well below the aircraft. This tends to keep the materials away from the induced turbulence, thus aircraft drift drops to the same magnitude as ground rig drift. WOOTEN (1961), in the Mississippi Delta, tested ground rigs with different nozzle arrangements. With a constant wind of 7 miles/h he found that a mist blower gave complete downwind coverage on the twelfth row of cotton but intermediate coverage on rows 1-11 and 13-17; a seven-nozzle air carrier sprayer gave complete coverage on rows 2-3 and 7-9 with incomplete elsewhere; while a four-nozzle air carrier sprayer gave complete coverage on rows 9-12 and incomplete elsewhere. Upwind coverage was fairly complete on the first few rows and incomplete elsewhere. Nearly all multiple row applicators, ground as well as aircraft, show these variable Agr. Meteorol.,2 (1965) 225-245

conditions. Variations in nozzles, speed of ejection of material, and speed of ino'..e ~ ment of the applicator, as well as particle size and weather, seem to cause an uneven d i s tribution. Research suggests that this variability is inherent in large-scale applicators. Physical f o r m or jormutation o f pesticide BROOKS' (1947) drift studies set a pattern that is followed today. He stated the principle: "Underlying all problems of field application of toxic materials is the rate of settling o f particles "suspended" in the air." Very small particles (up to 100 tt in diameter---a micron is I/25,000 inch) fall according to Stokes' law. Brooks adapted other research for larger particles and, in turn, this was adapted by AKESSON and YATES (1964b) and is shown in Table I. R. Z. ROLLLNS(1960) reported that a wind o f 3 miles/h would drift a 100-/t particle about 50 ft., while a l-/t particle would drift 84 miles. This is similar to Table I. As shown by Table i, dust particles are very small and offer a great potential for drift. Over 60 ~£ of all aircraft applications in the United States were in the form o f dust in the early 1940s. It is estimated that the percentage in 1963 had dropped to only 20 ~. When foliage is heavy, and when it is desirable to dust the underside of leaves as well as the top, dust applications are preferred over sprays. Electrostatic charging o f dust particles is being tested in some areas to increase the sticking power o f dusts. HARRELLet al. (1964) used an electrostatic duster mounted on a hi-clearance tractor to apply insecticide on sweet corn in southern Georgia. The initial concentration of dust on the corn plants was over one-third greater with either positively or negatively charged particles than with uncharged particles. These differences persisted for over 48 h, and the rate of residue decline with time was about the same for the three treatments. Generally, however, large field operations have shown only limited success for electrostatic chargers. Another experimental technique for reducing dust drift and increasing its sticking power is to wet the dust as it is ejected. Only limited success has been found here, too. When foliage is wet from rain or from dew, dusts tend to adhere to the surface better, but this does not reduce the drift potential.

TABLE I DRIFT POTENTIAL OF VARIOUS SIZE PARTICLES

(After AKESSONand YATES,1964b) Drop diameter (1~)

Particle type

Distance particle would be carried by a 3 miles/h wind while.falling loft.

400 150 100 50 20 10 2

Coarse aircraft spray Medium aircraft spray Fine aircraft spray Air carrier sprayers Fine spray and dusts Usual dusts and aerosols Aerosols

8.5 ft. 22.0 ft. 48.0 ft. 178.0 ft. 0.21 mile 0.84 mile 21.0 miles A gr. Meteorol., 2 (1965) 225-245

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Large particles also have some disadvantages. RIPPER (1955) showed that the percent of the target covered increased as the size of the droplet decreased. Granulars, which have about the same diameter as coarse aircraft sprays shown in Table I, have a very low drift potential. They do not stick to plant surfaces very well, however, and their concentration precludes their covering the ground. Their greatest efficiency is when applied to irrigated fields. They dissolve in the water and have proved quite effective in controlling mosquitoes and some other insects. The comprehensive south Texas drift experiments (ANONYMOUS, 1962) show that more pesticide was deposited on vertical plates with windy, stable conditions, and more on horizontal plates with light winds and turbulence. Also, more vertical deposition occurred close to the target suggesting that wind or horizontal transport is more important in border areas, and turbulent transport more important in distant areas. Contrary to the expected condition, droplet size was observed to be quite variable. In one test larger droplets were found on the plates 327 ft. distant from the sprayer than on the plates close to the sprayer. As the number of droplets was small, this may have resulted from chance. But it may have resulted from still another variab l e - e v a p o r a t i o n of droplets. Under turbulent conditions, droplets below a certain diameter may evaporate before they fall. Pure water droplets of variable diameter falling through air in a laboratory with a temperature 86 ° F and 50 ~ relative humidity had the following lifetime in seconds: 200/~, 56 sec; 100/t, 14 sec; and 50/x, 3.5 sec. AMSDEN (1962) demonstrated that additives greatly reduce the rate of evaporation. Detection of drift is a problem in itself, which also involves meteorology in the form of solar radiation. Fluorescent tracers have the desired sensitivity but many are unstable when exposed to solar radiation. YATES and AKESSON (1963) have worked out calibration curves for this problem. The south Texas study emphasized the need for collecting samples rapidly before they deteriorate.

Meteorological variables and drift Under field conditions, the applicator normally has little flexibility of choice of equipment or particle size. Management decisions usually have to be based on weather. If conditions are not favorable, he can wait for a change. Air movement is the most important variable to affect drift. Turbulence, as well as wind speed and direction, must be considered. Both must be measured at several locations and at several heights to give detail enough for a drift study. The extreme variability of both horizontal and vertical air movement makes precise detail impossible. But this observational error appears to be o f the same order of magnitude as the observational error o f many other variables considered as part of drift research. YEO and THOMPSON (1954) proposed a formula to approximate the measurement of turbulence. The temperature at 2.5 m was subtracted from the temperature at 10 m and added to the dry adiabatic lapse rate. This was then divided by the square of the average wind speed at 5 m. As an estimate of turbulence, Haddock (ANONYMOUS, 1962) tested three differ-

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RILEY A N D Vv. L. (ill i:v,

ent vertical temperature profiles. He subtracted the 5-ft. reading (which is the standard air temperature reading) from the soil surface temperature, the 2-inch soil temperature, and the 4-inch air temperature. The soil surface temperature gave the largest temperature lapse and appeared to be the best approximation of turbulence. These readings have the advantage of being easily accessible and fairly inexpensive. Temperature gradients measured in California experiments have been concerned with the difference between the 8-ft. level and the 32-ft. level (AKESSONand YATES, 1964a). If the 8-ft. level becomes more than 0.1°F warmer than the 32-ft. level, the air is unstable. A number of investigators have shown that irrigation modifies the local stability rather severely. SCHULTZet al. (1956) showed that daytime 5-ft. temperatures above irrigated rice fields are often 5°F lower than over dry land. The 1-inch soil temperature is as much as 30°F lower. Weeds are sprayed in California rice fields in the hot months of June, July, and August; so this difference in temperature profiles is of real importance. SCHULTZ et al. (1956) demonstrated the value of climatology in an application program. The hourly frequency of wind speed and direction are presented in graphical form for a number of rice growing areas. He went a step beyond this (ScHuLTZ et al., 1961) in demonstrating the effect of the delayed sea breeze in the target area. Many areas that receive pesticide applications are subject to mesoscale wind patterns, and as Schultz illustrated so well, applicators should be made aware of these wind patterns. Since wind normally increases with height, and most drift studies have measured winds at non-standard heights (in some cases the height is not even recorded), it is impossible to compare drift measurements in one area with another. Temperatures and temperature gradient measurements share this same lack of standardization. In most rowcrops, the tops of plants act as the boundarylayer as far as wind and temperature measurements are concerned. This being true, standard levels should probably be chosen in reference to the height of the crop. This poses many problems; not the least of which is: "what to do as the plants increase in height". Stable air is normally considered as precluding the dispersal of particles in the air. Actually some of the worst conditions of drift occur with stable air. BOURKEet al, (1960) stated: "High winds and stable air lead to maximum concentrations of airborne material at considerable distance downwind from the point of release." BROOKS (1947) had pointed this out previously and had indicated that dust penetration of the leaf canopy is also limited by an inversion. The Proceedings of the Annual Texas Agricultural Aviation Conference (AKF.SSON and YAT~S, 1964a) and Short Course on Pest Control is probably the most comprehensive collection of reports dealing with the application of pesticides. A number of papers stress meteorological implications. In addition to the many valuable individual contributions, the annual series, which began in 1952, gives a history of the subject by graphically depicting the advance of "the state of the art" through the years. Several excellent additions to the climatology of the United States, which have a bearing on drift, have appeared in recent years. HOSLER(1961) tabulated the frequenAgr. MeteoroL,2

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cies of inversions below 500 ft. for all Weather Bureau radiosonde stations. One set of seasonal maps shows the percentage of total hours when low level inversions occurred. Another set shows the maximum inversion frequency value reported at any o f the four daily observation times. Monthly maps showing the prevailing direction and mean speed of the wind have been published (U.S. WEATHER BUREAU, 1963b). These can be of real value to dusters and sprayers, especially those who move from one area to another as peak needs occur.

Diffusion research In meteorology, diffusion is defined as the exchange of fluid parcels between regions in space, in the apparently random motions of a scale too small to be treated by the equation o f motions (HusCHKE, 1959). Diffusion, in relation to atmospheric fallout and air pollution, is a large scale phenomenon in comparison with drift. Diffusion near the earth's boundary layer, in relation to the surface energy balance and evapotranspiration, is a comparatively small scale phenomenon. Both have received extensive study and the results can be applied to drift research. The U.S. WEATHER BUREAU (1963a) in cooperation with many other organizations is studying both scales of diffusion. Large scale diffusion research has the immediate aim of developing methods for predicting the concentration of noxious effluents, which are the airborne waste products o f our increasingly complex society. Analyses of wind and stability and the climatology of these elements are the basis of prediction. Turbulent conditions cause the effluent to swirl downward and reach the ground near the source, thus turbulence must be avoided. Inversion conditions, which permit long periods o f horizontal diffusion, allow the effluent to spread and thus dilute over a wide area. As mentioned in the previous section, inversion conditions are conducive to drift. Appearing before the California Senate Fact Finding Committee, AKESSON (1964) testified: "The worst weather conditions found so far are where an area temperature inversion exists combined with a low wind (under 5 miles/h). Here the drift residue downwind can be as much as ten times higher than that occurring during good weather conditions." Other studies suggest that light wind (under 5 miles/h) is not conducive to drift in itself, but it is normally associated with pronounced inversions that are conducive to long periods of particle suspension, and thus widespread diffusion. The fact that stability is favorable for stack disposal, but not for pesticides, is a result o f height of disposal and particle size. Stack particle concentration is reduced by an extemely wide area diffusion that is not possible in a low-level pesticide distribution. Smoke puffs have been used as visual indicators of particle transport prior to the release of radioactive wastes from a stack since the early 1940s. The Proceedings of the Texas Agricultural Aviation Conference showed how smoke puffers have been adapted to drift work. They are useful in research. In actual operations, they can serve as an inexpensive check on the actual drift of an application. In practice, how-

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ever, they are not used very often. But they would be of just as much value to drift operations as they are to the release of toxic material tYom a stack. Smoke puffers, though useful in controlling stack releases, have been supplemented by elaborate prediction models. The development of analogous micrometeorological prediction models in and near a plant canopy has suffered from one basic limitation. So far, it has not been possible to define the aerodynamic roughness effect of the boundary in terms of the height, density, and drag characteristics of the plant canopy. Most turbulence research workers define turbulent transport in terms of mean velocity and its derivatives. The logarithmic velocity profile represents the variation of the mean wind speed with height in the surface boundary layer. For fully rough flow, the profile may be approximated: P

p'

---- 1I n ( Z ) K

Zi>Zo._

where/,' is the friction velocity, K is von Karman's constant, and Zo is a constant called the roughness length, which is equal to the average height of surface irregularities divided by 30: The zero-plane displacement is an empirically determined constant introduced into the logarithmic velocity profile for the purpose of making the profile applicable to very rough surfaces. It is regarded as the datum height above which normal turbulent exchange takes place. It is comparable to the depth of the air layer trapped among the vegetation. KUTZBACH(1961) evaluated these variables in his now classic "bushel basket" experiments. Bushel baskets were placed at various distances from each other on a frozen lake surface. He showed that the roughness length and the zero-plane displacement increased with increasing basket density. Basic work has been reported from the U.S. Department of Agriculture in Ithaca, New York (SToLLZR and LEMOn, 1961; TAN and LING, 1961) and the U.S. Army Electronics Research and Development Activity, Fort Huachuca, Arizona (WRIGHT, 1964) where roughness parameters have been evaluated over flexible growing plants. They found in corn fields that the zero-plane displacement decreased (meaning that the wind penetrated deeper into the zone of obstruction) and the roughness length increased with increasing speed. In alfalfa, the opposite was true. In comparison with corn, alfalfa bends quite easily and in effect wind seals an alfalfa field, but penetrates deeply into a corn field. CIONCO et al. (1963) developed a model for wind flow in a plant canopy. They took into account many variations to be expected in different crops. Among other interesting findings was that certain critical wind speeds cause some crop canopies to open as the increasing wind speed orients the leaves along the flow. A prediction model for placement of any chemical application would be quite complex. For a high velocity application, either from an aircraft or a ground rig, the complexity would be extreme due to the short period of intense air movement followed by a long period of relatively slow air movement. Agr. MeteoroL,2 (1965)

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Eradica t ion programs

Most pesticide programs are control programs. The object is to hold the pest population below a certain maximum level. Eradication programs, however, have the aim o f eliminating the pest. To attain eradication, pesticides have been broadcast over wide areas. Drift is not a factor in a full-scale extermination program because the chemical is spread over the entire area. In pesticide literature, the gypsy moth project in the northeastern U.S.A. and the imported fire ant project in the south are the two most discussed eradication programs. In the mid-west, the Japanese beetle and the Dutch elm disease control programs approached the conditions of an eradication program. The gypsy moth program resulted in the widespread contamination of milk which persisted for at least 1 year. D.D.T. in an oil solution was aerially applied on nearly 1,000,000 acres in the northeast in 1956. In 1957, over 3,000,000 acres were treated with over 2,000,000 acres in New York State. HUDDLESTON et al. (1960) analyzed residues from this program. The chemical was found to be highly persistent on forage and little affected by weathering. The growth of new grass with its great increase in mass and volume was found to be a very important factor in residue loss. Wind is the primary factor in the progressive spread of the gypsy moth. The larval, or caterpillar stage, is extremely light and wind carries the insect during this stage to great heights and distances. The New England hurricane of 1938 is credited with spreading the moth from New Jersey into Pennsylvania and New York. Temperature and to a lesser extent moisture influence the development of the larval stage. This information could make control practices more specific. Chemical applications to eradicate the imported fire ant in the south have reportedly killed considerable wildlife and many species of insects. RHOADES (1963) made a detailed study of the effect of treatments of heptachlor in granular form by comparing treated and untreated ecologically similar areas. Samples were taken for 12 months before the treatment until 24 months after the treatment. In the treated area, the imported fire ant was eradicated. The number of other insects was severely reduced for several months following the treatment but returned to the approximate normal populations within 12 months and maintained these populations during the second 12-month period. The ants build large mounds. In winter they live near the top of the mound but in the hot summer they move deeper into the mound, lKhoades, University of Florida entomologist, and Davis, Weather Bureau agricultural meteorologist, have instrumented a project in northwest Florida to study mound temperature and moisture conditions, both of which are related to ant development and 'activity. The ants are most available during the queen's mating flight. Along the Gulf Coast, eight to ten mating flights occur each year, while 300-400 miles north of the coast there are only two to four mating flights during the year. The timing of the mating fright is influenced by weather. If accurate predictions are made of these flights, a short-lived chemical can be applied at the critical period and thus minimize the hazard to wildlife and other insect species. A~r. Meteorol., 2 (1965)

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Even the present knowledge of weather influence on fire ant activity can increase control efficiency and reduce residue hazards. The following is an example of al~ advisory distributed by the news medium in northwest Florida, southeast Alabama and south Georgia: WEDNESDAY U.S. WEATHER BUREAU F A R M WEATHER NOTES

MARCH 18, 1964

1000 AM EST QUINCY FLORIDA NORTHWEST FLORIDA

WEATHER CONDITIONS HAVE NOW BECOME RIGHT FOR A RAPID INCREASE IN F I R E ANT ACTIVITY. FIRE ANT ACTIVITY REMAINS QUITE D O R M A N T AS LONG AS SOIL TEMPERATURES ARE LOW. M E A N SOIL T E M P E R A T U R E S A R E NOW APPROACHING THE MID SIXTIES AT THE TWO- AND F O U R - I N C H LEVELS AND ARE IN THE LOWER SIXTIES AT THE EIGHT- A N D TWELVE-INCH LEVEL. THESE SOIL TEMPERATUllES A R E SUFFICIENTLY H I G H F O R THE H A T C H I N G OF NEW FIRE ANT BROODS-IN FACT THE FIRST NEW BROOD TO BE REPORTED WAS DETECTED THIS WEEK. W E A T H E R W l S E - - T H I S W O U L D BE A N EXCELLENT TIME TO APPLY CHEMICALS FOR CONTROL A N D ERADICATION OF THE FIRE ANT. F A R M E R S WANTING TO APPLY TREATMENT SHOULD CONSULT THEIR COUNTY AGENT FOR RECOMMENDATIONS.

Eradication programs for mosquitoes, gnats, the Japanese beetle and the Dutch elm disease often involve the food chain, This carries the pesticide's effect into unsuspected areas and much increased proportions. The Clear Lake California project is considered to be a classic example. Swarms of small gnats were a nuisance to people living around the lake. D,D.D. (Orthene 3-D, Rhothane) was applied in a limited control program in 1949. Increased applications were made in 1954 and 1957. The western grebe suffered from the latter two applications even though the grebes did not consume the D.D.D. directly. The grebes ate smaller carnivores which ate herbivores which in turn ate plankton which absorbed the poison from the water of the lake which reached the lake either from drift or rain wash. GEORGE (1964) stated: "Animals at the end of the complex ecological food chain seem particularly vulnerable."

ACTIVATION OF PESTICIDE CHEMICALS

All pesticides have temperature, moisture and radiation thresholds that influence the rate of chemical activity which in turn affects the efficiency. Weed and brush control along highway and railroad rights-of-way consume a large volume of herbicides. AI4RENS(1963)devoted a section of the Connecticut Bulletin on roadside weed and brush control to the influence of weather. Ahrens states: "Weather conditions cannot be ignored in the application of roadside herbicides." Soil moisture promotes the efficiency of soil sterilant and preemergence herbicides, Moisture encourages weed seed germination and enables chemicals to kill seedlings before they emerge. Moisture following an application carries the chemical below the surface where it may contact either roots or seeds. Agr. Meteorol., 2 (1965) 225-245

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Rainfall immediately after an application is beneficial if it is not heavy enough to wash away the chemical. With foliar herbicides such as the phenoxy compounds, dalapon, amitrole and others, the opposite is true. Rainfall immediately after an application is likely to wash off the chemical. If foliage is wet before application, the chemical is also likely to wash off. By contrast, however, high humidity increases the absorption and decreases the evaporation of the carrier of foliage sprays. Also, adequate soil moisture is necessary for efficient foliar applications. Translocation of the phenoxy compounds in particular is greatest when root activity is high and the plants are growing vigorously. BATJER and BmLtNGSBY(1964) devote a section to weather in their Washington State University Bulletin on apple thinning. They state: "Weather before and after spraying is a major factor in the great variability which often results from thinning sprays." Rain after a spray application of dinitro materials rewets the material and results in increased absorption and sometimes results in serious foliage injury and excessive reduction in fruit set. The sooner the rain arrives after the sway dries, the greater the damage. Absorption of D.N.O.C. increased as the length of the rainy period increased from 1 to 20 h. Greater thinning has been observed in areas of the same orchard where poor air drainage caused the leaves to remain wet longer than in more favored sections. High humidity also favors thinning action. WESTWOODet al. (1960) showed that a few days of 100 % relative humidity increased D.N.O.C. absorption by modifying the condition of the leaf cuticle. Rain at 70°F after a D.N.O.C. spray gives greater absorption than at 50°F. Temperatures near the freezing point increase flower kill in D.N.O.C. sprayed areas, also N.A.A. absorption increased when apple trees were exposed to temperatures near 28°F a few days before spraying. The West Virginia Spray Bulletin (H. A. ROLLINSet al., 1964) emphasizes the danger thus: "Following low temperature conditions (28-31°F) chemical thinning sprays should be used with caution and at reduced rates if at all." The same bulletin states that apple scald inhibitors should not be sprayed when the temperature is over 80°F because of possible staining or spray burning. Light affects the efficiency of many chemical pesticides. High values of light break down some unstable chemicals. Light also affects the action of chemicals as they enter the plant. JORDAN et al. (1960) found that low light intensities and high temperatures increased the sensitivity of flax plants in Minnesota to 2,4-D. SCHAEFER et al. (1963) tested herbicidal action on the smooth-leaved perennial ground-cherry in Idaho. By keeping the plants in the dark for various periods of time, they reduced the starch level to near zero. This has been considered as an influence on the rate of herbicide absorption but they found no discernible differences. R.O. Thomas (personal communication, 1964) has found that the chemical action of many cotton defoliants is influenced by a combination of both temperature and sunlight. On nights when the temperature drops below 60°F, leaves may be killed Affr. MeteoroL, 2 (1965)

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by the defoliant but the rate of leaf drop is much reduced. If the following day is sunny, the detrimental effect of the low nighttime temperature is reduced; if cloudy, the effect is increased. Leaf temperature, which is influenced by sunshine as well ~s air temperature, may explain some of the combined temperature-sunlight relationships. Many relationships that have been based solely on air temperature have bee~ refined recently by also considering solar radiation. No doubt, even this dual relatio~ is not a complete picture. The true relationship is often a complex of many weather variables. D.D.T. will control a great many cotton insects but control of thrips has been unsatisfactory when the temperature is above 90°F (NATIONAL COTTON COUNCIL, 1964). The same booklet reports that Tetradifon will control some species of spider mites but the action is very slow with a temperature below 90°F. When more than one pesticide acts upon a pest or its host, the toxicity may be greatly increased. This process is called potentiation. Temperature influences not only the toxicity of most pesticides individually but affects the potentiation process. YOUNG and RouSSEL (1958) in testing combinations of insecticides on both resistant and susceptible boll weevils found that endrin and malathion together were antagonistic at 90°F but showed a synergistic effect at 60°F and 80°F. When toxaphene and malathion were combined, the effect was reversed; the action was antagonistic at 60°F but showed a synergistic effect at 80'-~Fand 90°F. Temperature also affects the pesticide-animal relationship. The PesticideWildlife Studies, edited by GEORGE (1963) is a comprehensive report of the subject. For example, the echo (effective concentration 50 is the concentration of toxicant in the environment which produces a designated effect to 50 ~ of the population of test organisms exposed to it) of heptachlor that was lethal to sunfish ranged from 0.017 mg/l of water for 96 h of exposure at 75°F to 0.092 mg/l of water for 24 h exposure at 45°F. Higher temperatures caused increased toxicity for both heptachlor and kepone. Each chemical has an optimum temperature range. The literature abounds with specific temperature-pesticide reactions and each chemical must be considered individually.

REMOVAL AND INACTIVATION OF PESTICIDES

Residue is a much discussed problem in the use of pesticides. A chemical can be removed physically by wind, rain or volatilization. It can be inactivated by absorption or it can be changed into a different chemical by photochemical or biological actions or by the action of another chemical. Rain wash is probably the most frequent method of physically removing a chemical after it has been correctly located. As discussed before, the effect of rain is complex. A little drizzle or very light rain may help hold the chemical. Further, it may promote chemical absorption by softening the desired surface. Agr. MeteoroL, 2 0 9 6 5 )

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Rain decreases pesticide efficiency when drop impact dislodges the chemical particles or when the volume is sufficient to float away the particles. One-fourth inch of rain that falls in 5 min will wash away more chemical than one-fourth inch of rain spread over 24 or 48 h. Pesticide literature contains many references to dilution by rain but the intensity of rain is seldom reported, and, in some cases, even the amount is not considered. Wind is a primary factor in placement of pesticides, but it is also a factor in removing the chemical once it has been properly located. This is especially important for liquid pesticides after they have dried following placement. MISTRtC and GAINES (1954) tested the effect of wind on the toxicity of emulsion sprays of toxaphene, dieldrin and endrin on the boll weevil and the salt-marsh caterpillar. With wind, the toxicity of toxaphene was reduced more than the other; without wind, it was least reduced. They stated: "Wind, therefore, appeared to be the most important climatic factor studied which reduces the toxicity of toxaphene." Solar radiation, temperature and relative humidity affect volatilization of pesticide chemicals. The degree of each required for volatilization depends on various characteristics of the chemical. Very little research has been reported on this complex phenomenon. Physical removal of a foliar pesticide is related to the character of the leaf. WILSON and HEDDEN (1963) reporting on their tests in Ohio of adhesion of pesticides to many different plant leaf surfaces found great variation. A pubescent leaf such as eggplant was found to initially intercept and hold twice as much spray material as a smooth leaf such as a pepper plant. It retained three times as much of the spray material for a period of several days. Smooth-leaved plants should be sprayed more frequently and with a heavier dose if they are to receive a degree of control comparable to a hairy leaved plant. SHEETS (1962) reviewed the subject of disappearance of substituted urea herbicides from soil. He concluded that the processes that promote inactivation are: absorption and metabolism by soil micro-organisms, adsorption to mineral and organic colloids, leaching by rain or irrigation, chemical reactions (non-biological), photochemical alterations, volatilization, and absorption by higher plants. These processes are influenced by soil properties--types and amounts of clay, minerals, structure, texture, organic matter, temperature, moisture and pH; herbicide properties--water solubility, structure, reactivity, charge and polarity; and environmental variables--rainfall, irrigation, temperature, light and wind. Herbicide persistence in the soil varies considerably in different micro-environments. Soil moisture is a major factor in inactivating the phenylurea herbicides. Besides the diluting effect of carrying this chemical deeper in the soil, moisture promotes growth and reproduction of soil micro-organisms that act upon the chemicals. The total process is complex and, at times, one effect of soil moisture may contradict another. For example, the lack of rainfall or irrigation, and thus a resulting lack of soil moisture, may reduce the effectiveness of pre-emergent herbicides. The reduction can Affr. Meteorol., 2 (1965)

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result from solar radiation induced inactivation. At times this is augmented i~} volatilization. WELDON and TIMMONS (196l) showed that exposure of crystalline monuron and diuron to radiation for 28 h decreased the biological activity 75 O/o.Photodecomposition might explain the loss of monuron from the soil surface in arid areas, while in humid areas frequent rains limit the decomposition by carrying the chemicals imo the soil. A dry period of 2 weeks or more has been shown to reduce the effectiveness of diuron as a pre-emergent herbicide in humid areas. However, this reduction may result from volatility losses also. Removal of pesticides is a much less documented phase of the pesticide problems as compared with the placement phase. Public hearings on pesticides held in Memphis, Baton Rouge and New Orleans in the spring of 1964 emphasized the lack of precise data on this phase. There are so many combinations of rain, wind and sunlight, as well as biological factors, that it is difficult to compare one case with another. Also, some of the analysis techniques for finding pesticide residues are not precise. Added to this, some chemical constituents associated with certain pesticides are produced naturally. A number of analyses have pointed out these complications by finding a larger volume of chemical residue than was originally applied. A G R I C U L T U R A L M E T E O R O L O G I C A L M O D I F I C A T I O N OF NEEDS F O R PESTICIDES

Weather, directly or indirectly, is one of the most important factors to affect insects, diseases, and weeds. Weather exercises a natural control over many pests. But of even greater potential importance, weather influences the vulnerability of pests to control practices. Through the use of agricultural meteorology, an applicator may be able to catch the pest in an easily accessible location or in a particularly sensitive condition. None of the six major citrus mite pests in California is distributed throughout all of the citrus-growing areas. Extreme weather conditions in the various areas limit their distribution. Weather also dictates the way they are controlled. The citrus bud mite is confined to the coastal districts. NormaUy, it is further confined under the bud bracts of the citrus tree. During periods of migration to new buds, which occur during certain weather conditions, these mites may be fairly easily controlled. Residual type acaricides applied as mist sprays give effective control. At other times, however, the spray must wet the buds in order to contact the mites and obtain adequate control. This requires a full coverage type application. The adult and nymphal stages of citrus red mite, which inhabit interior areas, are reduced by hot, dry winds. This leaves the remaining population largely in the egg stage. Control applications properly timed following these adverse weather conditions result in more effective control of this mite than is normally obtained. JEPPSON (1964) found that lemon fruit are affected in their sensitivity to mites by extremes in weather. This is in addition to the effect weather has on the mite. Green lemon fruit that had been subjected to hot, dry weather in the field were brought into the laboratory and found to be less favorable for mite egg production than similar Agr. Meteorol.,2

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fruit obtained from cool, moist coastal orchards. Also, lemon tree leaves were less susceptible to the mites. Thus it appears that weather extremes adversely affect not only mite populations directly but alter host favorability. RAINEY (1963) related the biology and behavior of the Desert Locust to weather. In this comprehensive report, he traced the locusts' movements on the macro- and mesowind field scales. This thorough knowledge of a pest and its relation to weather enables the control agency to increase its efficiency. Cotton boll rot is a major factor in reducing quality and quantity. It is most prevalent just before harvesting time. NEWTON and RANr~EY(1964) reported that the degree of boll rot infection is intimately related to the microweather within the plant zone. Measurements made in Mississippi showed that increased light, wind and temperature, and decreased relative humidity reduced the amount of the boll rot fungus. Defoliation, which is commonly practised before harvest time, allows more sunlight penetration within the crop zone and permits greater ventilation. This process leads to a reduction of boll rot infection. Experiments with super-okra-leaved cotton, which also permits more ventilation and sunlight penetration, may lead to similar reduction of fungus damage. Skip row planting, featuring one, two, four, or more rows of a crop planted alternately between some number of unplanted rows, has resulted in increased quality and yield. Skip-row crops increase the amount of light reaching the plant and increase the ventilation. This, in turn, reduces some insect populations, some disease developments, and makes weed control less expensive. Cultural practices may, as in this case, reduce the requirement for pesticides. The over-wintering stage of many pests is a particularly vulnerable one. Since many pests could not withstand the rigors of winter except for the protective microweather conditions in which they inhabit, the destruction of these over-wintering habitats would reduce pest population. DEWtTT and GEORGE (1960) in their Pesticide-Wildlife Review mentioned a number of other control methods; planting and harvesting at particular times, proper fertilization and manipulation of water levels, and rotation of crops. Each practice tends to impose natural controls on many pests. The various weather thresholds which affect pest development must be evaluated in terms of the specific pest. Modification of cultural practices which will cause unfavorable pest microweather conditions can then be adopted and the use of chemical pesticides may be reduced. From time to time, biologists ask why there isn't a biological classification of climate for all agricultural areas. Since most pests grow in a modified microclimate, it would be physically impossible to classify all farming areas by any practical number of climatic variables. LANDSBERG(1962) stressed that there can be no universally valid climatic classification that can be applied to all biological processes. He further pointed out that biologists have rarely defined the exact climatic conditions that influence the particular process on which they are working. Until this is done, the vast amount of climatological information, which is now available for most agricultural areas in the country, can be of only limited use to the biologist. Agr. Meteorol.,2 (1965) 225-245

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ADVISORIES

Most chemical applicators apply the widespread American hobby of "do-it-yoursell to the principle of dusting and spraying weather advisories. This is a necessity ha many areas because formal advisories are issued only for limited areas of the country, Recent expansion of the Weather Bureau's specialized agricultural weather service has produced operational advisories in a number of areas and specialized dusting and spraying advisories are an important phase of this service. WHITE(1964), Chief of the U.S, Weather Bureau, stated: "Weather forecasts are extremely perishable. The Weather Bureau thus has a problem similar to that of the vegetable grower. Its product must reach the consumer quickly... A teletypewriter circuit has been set up in each agricultural weather service area. Operating 24 hours a day throughout the year, the circuit brings timely weather information to radio and television stations and newspaper offices in the area... The dusting and spraying advisories emphasize weather conditions for low-level aircraft flights as well as those factors important to application of agricultural chemicals." The following is one of these advisories that is distributed to growers and applicators through the news media of radio and TV: ....

5 : 00 A M

MONDAY

SEPTEMBER 9, 1964

A G R I C U L T U R A L AVIATION ADVISORY FOR MID-SOUTH CLEAR SKIES A N D LIGHT WINDS GAVE IDEAL RADIATION CONDITIONS LAST NIGHT. HEAVY DEW COVERS MOST AREAS. G R O U N D FOG F O R M E D OVER M U C H OF THE LOUISIANA DELTA, SOUTHEAST ARKANSAS AND NORTH A N D CENTRAL MISSISSIPPI AND VISIBILITY IS R E D U C E D TO ONE TO THREE MILES, BUT WILL INCREASE TO SIX MILES OR BETTER BY 7 : 30 AM. SKIES WILL BE CLEAR TODAY EXCEPT FOR ONE TO THREE-TENTHS OF C U M U L U S CLOUDS AT 3500 FEET. D E W WILL DRY BY 9 AM. WINDS WILL BE LESS T H A N 5 MPH TILL 9 AM, WILL BE SOUTH 7 TO 10 MPH 9 A M NOON, SOUTH 10 TO 15 MPH THIS A F T E R N O O N BUT LESS THAN 5 MPH BY 6 PM. NO RAIN TODAY OR TUESDAY BUT ABOUT A THIRD O F THE AREA WILL HAVE SHOWERS WEDNESDAY. GOOD D U S T I N G A N D SPRAYING CONDITIONS TODAY TILL 9 AM A N D A F T E R 6 PM. DEW WILL BE MODERATE TO HEAVY TONIGHT. TEMPERATURES WILL BE 70 DEGREES OR H I G H E R A N D CONDITIONS ARE FAVORABLE FOR APPLYING DEFOLIANTS. THE EXTENSION SERVICE ADVISES THAT BOLLWORMS A R E STILL PREVALENT IN MANY YOUNG, G R E E N COTTON FIELDS A N D SHOULD BE CONTROLLED. SOME OLDER, D R Y FIELDS DO NOT NEED CONTROL. IF IN DOUBT, CALL YOUR COUNTY AGENT.

Typical weather map patterns are associated with favorable weather for applying dusts and sprays, BOtrR~E (1957) carried the weather map pattern system a step further. He pioneered the process of going directly from a synoptic weather map to a plant disease advisory, P a s t outbreaks of potato blight in Ireland were related to certain map features. When these typical features are expected to occur, he issues a blight forecast. This principle was extended to the 700 mbar chart in the northcentral United States, by WALLINand RaLEV(1960). SCARPAand RANmRE(1964) expanded ~ r . Meteorol., 2 (1965) 225-245

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this s y n o p t i c a p p r o a c h t o t h e 500 m b a r c h a r t t o m a k e r o u t i n e a d v i s o r i e s f o r d o w n y m i l d e w o f l i m a b e a n s in N e w Jersey. BOUR~E (1962) c o m m e n t e d o n t h e s y n o p t i c p a t t e r n p r i n c i p l e thus: " I t seems to m e p a r t i c u l a r l y unwise, to say t h e least o f it, to a t t r i b u t e m e r i t to m e c h a n i c a l devices b a s e d o n a n y ' m o d e l ' o f d i s e a s e - w e a t h e r r e l a t i o n s h i p , i f t h e s e are t o be u s e d as a u t o m a t i c a l a r m signals b y u n i n f o r m e d g r o w e r s . T h e c o n s e n s u s r e p o r t e d in the l i t e r a t u r e is t h a t a c c u r a t e , timely, easily u n d e r s t o o d a g r i c u l t u r a l w e a t h e r a d v i s o r i e s are n e c e s s a r y if p e s t i c i d e a p p l i c a t i o n s are to be efficient as well as s a f e . "

REFERENCES AHRENS, J. F., 1963. Chemical control of weeds and brush along roadsides. Conn. Agr. Expt. Sta., New Haven, Bull., 624 (revised) : 28. AKESSON,N. B., 1964. Pesticide drift residue. Aerial Applicator, 2 (3) : 5. AKESSON, N. B. and YATES, W. E., 1964a. Pesticide drift and residue problems in relation to aircraft applications. Proc. Ann. Tex. Agr. Aviation Conf., 13th : pp.F-1-F-16. AKESSON, N. B. and YATES,W. E., 1964b. Problems relating to application of agricultural chemicals and resulting drift residues. Ann. Rev. Entomol., 9 : 285-318. AMSDEN, R. C., 1962. Reducing the evaporation of sprays. Agr. Aviation (The Hague), 4 : 88-93. ANONYMOUS, 1962. Investigation of the pesticide drift problem in the lower Rio Grande Valley of Texas. Tex. Agr. Mech. Coll., MP-620 : 61 pp. BATJER, L. P. and BILLINGSBY,H. D., 1964. Apple thinning with chemical sprays. Wash., State Univ., Bull., 651 : 7-9. BOURKE,P. M. A., 1957. The use of synoptic weather maps in potato blight epidemiology. Irish Dept. Ind. Commerce, Meteorol. Serv., Teeh. Note, 23 : 35. BOURKE,P. M. A., 1962. Plant diseases and pests as influenced by weather. In: S. W. TROMP (Editor), Biometeorology. Pergamon, London, pp. 153-161. BOURKE, P. M. A., ASHTON,H. T., HUBERMAN,M. A., LEAN, O. B., MAAN, W. J. and NAGLE, A. H., 1960. Meteorological service for aircraft employed in agriculture and forestry. W. M. 0. Tech. Note, 32, 96 TP 40 : 1-32. BROOKS, F. A., 1947. The drifting of poisonous dusts applied by airplanes and land rigs. Agr. Eng., 28 (6) : 233-239. CIONCO, R. W., OHMSTEDE,W. D. and APPLEBY, J. F., 1963. A model for wind flow in an idealized vegetative canopy. U. S. Army Electron. Res. Develop. Activity, Meteorol. Res. Notes, 5 : 35 pp. COLE, U C., 1964. Pesticides: a hazaid to nature's equilibrium. Am. J. Public Health, Suppl., 54 (1) : 24-31. DARBY, W. J., 1964. Pesticides: a contribution to agriculture and nutrition. Am. J. Public Health, Suppl., 54 (1) : 18-23. DEWITT, J. B. and GEORGE,J. L., 1960. Pesticides-wildlife review. U. S. Fish Wildlife Serv., Circ., 84 : 36 pp. D1MOND, A. E., REYNOLDS, H. T. and ENNIS, W. B., 1964. Report on fifth international pesticide congress, London. Science, 143 (3602) : 151--155. EGLER, F. E., 1964. Pesticides--in our ecosystems. Am. Scientist, 52 (1) : 110-136. GEORGE, J. L. (Editor), 1963. Pesticide-wildlife studies. U. S. Fish Wildlife Serv., Circ., 167 : 109 pp. GEORGE, J. L., 1964. Ecological implications of the use of chemicals to vertebrate wildlife. Penna. State Univ. HALLER¥, H. L., 1964. Pesticides: the challenge, how do we meet it? Am. J. Public Health, Suppl., 54 (1) : 37~41. HARRELL, E. A., BOWMAN,M. C. and HARE, W. W., 1964. Field Evaluation of an Electrostatic Duster. Proceedings of Southern Agricultural Workers' Conference, Atlanta, Ga., 12 pp. HOSLER, C. R., 1961. Low-level inversion frequency in the contiguous United States. Monthly Weather Rev., 89 (9) : 319-339.

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HUDDLESTON, E. W., (}YRISCO, (.~. G. and Lls~, D. J., 1960. D.D.T. residues on New York dai~y farms following the gypsy moth eradication program. J. Econ. Entomol., 53 (6) : 1019-102J. HUSCHK~, R. E. (Editor), 1959. Glossary q[' Meteorolq¢y. Am. Meteorol. Soc., 638 pp. JEPPSON, L. R., 1964. Acaricides for citrus mite control. Agr. Chem., 19 (12) : 81-84. JORDAN, L. S., DUNHAM, R. S. and LINt'K, A. J., 1960. Effects of the interaction of varying temperatures and light response of flax to 2,4-D. ~4in., Univ., A~r. Exp. Sta., Tcch. Bull., 237 : 23 pp. KUTZBACH, J. E., 1961. Investigations of the modification of wind profiles by artificially controlled surface roughness. In: Studies of the Three-Dimensional Structure q[" the Planetary Buundw T Layer -Wisconsin, Univ., Attn. Rept., 61 : 71 113. LANDSBERG, H. E., 1962. Discussion of old and new principles of phytobiological climatic classification. In: S. W. TR()Me (Editor), Biometeorolq~y. Pergamon, London, 146 pp. MISTRI¢, W. J. and GAINES, J. C., 1954. Effect of weather factors on the toxicity of certain insecticides J. Econ. Entomol., 47 : 646 650. NATIONAL COTTON COUN(IL, 1964. Cotton Pest Control Guides. 34 pp. NEWTOr~, O. H. and RANNEV, C. D., 1964. The effect of bottom defoliation on the microclimate. Proc. Ann. Beltwide Cotton Defoliation Pkysicol. Conf., 18tk, Memphis, Tenn., pp. 2t-25. PRES~I)ENT'S SCIENCE ADWSOR¥ COMMITTEE, 1963. The Use of Pesticides. The White House, Washington, D.C., 25 pp. RAINEY, R. C., 1963. MeteoIology and the migration of desert locusts. W.M.O. Teck. Note, 54, 138 TP 64 : 109 pp. RnOADES, W. C., 1963. A synecological study of the effects of the imported rite ant eradication program II, light trap, soil sample, litter sample and sweep net methods of collecting. Florida Entomologist, 46 (4) : 301-310. RapPER, W. E., 1955. Application method for crop protection chemicals. Ann. Appl. Biol., 42 : 288-324. ROBERTS, S. C. and SMITH, M. R., 1963. The evaluation of a positive energy distribution system for the aerial application of solid materials. Mississippi State Univ., Aeropkys. Res. Note, 20 : 31 pp. ROLLINS, H. A., B o ~ , M. L., DRAKE, C. R., GROVES, A. B. and HILL, C. l-l., 1964. West Virginia spray bulletin for tree fruits. West Va. Coop. Extension Serv., Circ., 400 : 36 pp. ROLLINS, R. Z., 1960. Drift of pesticides. Calif., Dept. Agr., Bull., 49 (1) : 34-39. SCARPA, M. J. and RANIERF~, L. C., 1964. The use of consecutive hourly dewpoints in forecasting downy mildew of Lima Bean. Plant Disease Reptr., 48 (2) : 77-81. SCHAEFER, R. J'., YOUMANS, G. W. and E~CKSON, L. C., 1963. The Smooth-Leaved Perennial Groundcherry. Idaho Univ. Agr. Expt. Sta., Res. Bull., 414 : 17 pp. SCHULTZ, H. B., AKESSON, N. B. and YATES, W. E,, 1961. The delayed "sea breezes" in the Sacramento Valley and the resulting favorable conditions for application of pesticides. Am. Meteorol. Soc., Bull., 42 (10) : 679 ~687. SCHULTZ, H. B., AK~SSON, N. B., YATES, W. E. and INGEBRETSEN, K. H., 1956. Drift of 2,4-D applied by plane. Calif. Agr., 10 (8) : 4-14. SHEETS, J. T., ! 962. Metabolism of herbicides, review of disappearance of substituted urea herbicides from soil. J. Agr, Food Chem., 12 : 30-33. STOLLER, J. and LEMON, E., 196l. Turbulent transfer characteristics of the airstream in and above the vegetative canopies of the earth's surface. In: Energy Balance at the Earth's Surface, Final Rept.---U. S. Dept. Agr., Ithaca, N.Y.,21 pp. TAN, H. S. and LLNG, S. C., 1961. Quasi-steady micro-meteorological atmospheric boundary layer over a wheat field. In: Energy Balance at the Earth's Surface, Final Rept.--U. S] Dept. Agr., Ithaca, N. Y., 17 pp. U. S. DEeARTMENT OV AGRICULTURE, 1963. Pesticide-production and trade in the United States. Agricultural Statistical Yearbooks 1950, 1955 and 1963, 362 pp. U. S. WEATHER BUREAU, 1963a. Research Progress and Plans of the U. S. Weather Bureau, Fiscal Year 1963, pp.81-88. U. S. WEATHER BUREAU, 1963b. Prevailing Direction, Mean Speed, and Fastest Mile of Wind. Sheet of the National Atlas of the United States, Monthly and Annual Maps, 1 p. WALLIN, J. R. and RILEY, 3". A., 1960. Weather map analysis--an aid in forecasting potato late blight. Plant Disease Rept., 44 (4) : 227-234. WELDON, L. W. and TIMMONS, F. L., 1961. Photochemical degradation of Diuron and Monuron. Weeds, 9 : lll~ 116.

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WESTWOOD,M. N., BATJER,L. P. and BILLINGSBY,H. D., 1960. Effects of environment and chemical additives on absorption of Dinitro-O-Cresol by apple leaves. Proc. Am. Soc. Hort. Sci., 76: 30-40. WHrrE, R. M., 1964. Space age weather forecasts; how the weather bureau serves agriculture. 1964 Yearbook, United Fresh Fruit Vegetable Assoc., pp.52-57. WILSON, J. D. and HmDEN, O. K., 1963. Leaf character as it influences spray deposition and adhesion. Plant Disease Reptr., 47 (8) : 732 735. WOOXEN, O. B., 1961. Air carrier sprayer operation. S-2 Pro/ect Cotton Mechanization 1961, Ann. Rept., pp.339-341. WRIGHT, J. L., 1964. The determination of shear stress, transfer coefficient, and mixing length values within a crop using mean wind velocity profile. Meeting Res. Micrometeorology, 6th U. S. Army Electron. Res. Develop. Activity, 12 pp. YAT~S, W. E. and AKESSON, N. B., 1963. Fluorescent tracers for quantitative microresidue analysis. Trans. Ant. Soc. Agr. Engrs., 6 (2) : 104-114. YEO, D. and THOMPSON, B. W., 1954. Aircraft applicators of insecticides in East Africa. Bull. Entomol. Res., 45 (1) : 79 92. YOUNG, M. R. and ROUSSEL, J. S., 1958. The effects of temperature on the efficiency of insecticides applied topically to boll weevils differing in susceptibility to chlorinated hydrocarbon insecticides. J. Econ. Entomol., 51 (1) : 93-100.

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