The response of onion couch (Arrhenatherum elatius ssp. bulbosum (Willd.) Schub. & Mart.) to glyphosate and other foliage-applied herbicides

CROP PROTECTION (1985) 4 (2), 263-271

The response of onion couch (Arrhenatherum elatius ssp. bulbosum (Willd.) Schub. & Mart.) to glyphosate and other foliageapplied herbicides P. AYRES

AFRC Weed Research Organization, Begbroke Hill, Yarnton, Oxford OX5 7PF, UK Abstract. Two experiments were conducted in which foliage-acting herbicides were applied to onion couch (Arrhenatherum elatius ssp. bulbosum). The first experiment used an artificially established population and investigated the effects of straw burning on the performance of autumn-applied treatments of glyphosate, aminotriazole and dalapon. Spring barley was sown without cultivation. The second experiment, conducted on a naturally occurring infestation, compared the performance of glyphosate applied at alternative autumn timings and a single application of flamprop-methyl made in the following spring, in the presence of a winter wheat crop. In the first experiment, assessments made after 15 months suggested that straw burning resulted in increased growth. In addition, herbicide performance appeared less effective after burning. In neither case were these differences significant. Glyphosate at 1-0 and 1"5 kg a.e./ha gave the highest levels of control of both shoots and bulbs, whereas control from aminotriazole at all doses (1-5, 3-0 and 4-5 kg a.i./ha) was poor. Dalapon (6"0, 12.0 and 18"0 kg a.i./ha) was intermediate in its effectiveness. In the second experiment, applications of glyphosate at 1-0 and 1.5 kg a.e./ha resulted in high levels of control of both shoots and bulbs with no significant difference between application dates. Flamprop-methyl at 0.52 kg a.i./ha reduced the number of shoots and bulbs by 55% and 580/0 respectively. All treatments significantly reduced the number of inflorescences present in July.

Introduction A survey o f the distribution of onion couch in arable regions o f the United K i n g d o m (Ingram, 1975) indicated that although nationally it is not an important weed, locally it has been shown to be both troublesome and difficult to control. T h e use o f glyphosate (N-(phosphonomethyl)glycine) to control the regrowth of perennial grass weeds in cereal stubbles in the a u t u m n was introduced to the 0261-2194/85/02/0263~)9503.00 © t985 Butterworth& Co (Publishers)Ltd

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Effect of herbicideson onion couch

United Kingdom in the early 1970s (Evans, 1972). Although there is considerable evidence for the effectiveness of glyphosate against common couch (Elymus repens) there is little or no information on the response of onion couch (Arrhenatherum elatius ssp. bulbosum) to this or other foliage-acting herbicides when applied at this time. The changing pattern of cereal production, with greater emphasis on winter varieties, has meant that the time interval between harvest and sowing in the autumn may be too short to allow sufficient regrowth of onion couch to occur and this could result in poor control. Observations by the Agricultural Development and Advisory Service (ADAS) suggest that herbicides may be less effective on onion couch than on common couch when applied at this time of year (D. W. Beesley, personal communication). Reduced cultivations and direct drilling allow greater flexibility in treatment timing but both favour the growth and development of onion couch (Ayres, 1977). In addition, onion couch in undisturbed soil often exhibits a low ratio of foliage area to numbers of bulbs (Ayres, 1977) and this may influence the translocation of some foliage-applied herbicides. Stubble burning, a prerequisite for successful direct drilling, is also of considerable interest as this may modify the growth of the regenerating shoots. The control of onion couch by herbicides used primarily against wild oats (Avena spp.) is also important because these herbicides offer selective control in cereal crops. Some herbicides, notably benzoylprop-ethyl (ethyl N-benzoyl-N(3,4-dichlorophenyl)-DL-alaninate), flamprop-M-isopropyl (isopropyl N-benzoylN-(3-chloro-4-fluorophenyl)-D-alaninate) and flamprop-methyl (methyl Nbenzoyl-N-(3-chloro-4-fluorophenyl)-DL-alaninate), have been observed to reduce numbers of inflorescences (B. J. Wilson, personal communication) but there is little information on the magnitude of this effect and no evidence of any effect on the bulbs, which are the main method of propagation. This paper describes two experiments in which glyphosate was applied to onion couch regrowth after cereal harvest. The first experiment, using an artificially established population in spring barley, investigated the effects of straw burning on the performance of glyphosate, aminotriazole (1//-1,2,4-triazol-3-ylamine) and dalapon (2,2-dichloropropionic acid). The second experiment was conducted on a naturally occurring population. Glyphosate was applied at two dates in the autumn before winter wheat was drilled, and a single application of flampropmethyl was made in the following spring. Materials and methods

Experiment 1 Treatment and design. The experiment was sited at Begbroke Hill on a sandy loam overlying gravel. A randomized split block design was used, with three replicates. The main plots measured 22 x 6 m and were separated by pathways measuring 2 m. Each main plot was split into two sub-plots measuring 22 x 2.5 m, with a 1 m discard area between them. These sub-plots were further sub-divided into 11 areas, 2-5 x 2 m, of which the central 1.4 × 1 m was planted with onion couch bulbs. The total experimental area was 22 x 22 m. Bulbs of onion couch were collected in a field near Enford, Hampshire from a population of extreme bulbous form. These plants were washed free of soil and pieces required for planting were selected for uniformity of bulbs and shoots.

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Following an application of a compound fertilizer (75 kg/ha N, 38 kg/ha P205 and 38 kg/ha K20 ) and light cultivations, all plots were sown with spring barley (cv. Julia) at 134 kg/ha on 24 March 1975. The day after cereal drilling the pieces of onion couch were planted into the central 1.4 × 1 m areas of each 2.5 × 2 m plot at intervals of 20 cm at a depth of 5 cm. The mean number of shoots and bulbs planted were 64/m 2 and 46/m z respectively. After planting, the experimental area was rolled using a light tractor with a set of Cambridge rolls. During July and early August the inflorescences were removed to prevent seed shedding. After the barley harvest on 4 August 1975, the straw was baled from the entire experiment. Three days later, sub-plots designated to receive the burning treatments were uniformly spread with approximately half the amount o f straw removed from the whole experimental area, and burnt. A uniform burn was achieved over all these plots. Herbicide treatments (see Table 2) were applied on 7 October 1975 using a propane,pressurized small-plot hydraulic sprayer with a 2 m boom fitted with four Spraying Systems 6502 'Teejet' nozzles. Applications were made at a spray volume of 300 f/ha and at a pressure of 210 kPa. In the following spring the experimental area was direct drilled with spring barley (cv. Julia) at 154kg/ha o n 27 February 1976. In both seasons a spring application of nitrogen (92 kg/ha) was applied and spraying for dicotyledonous weed control was carried out where necessary.

Assessments. Fixed square metre quadrats placed in the middle of the 1-4 × 1 m planted area of each plot were used for all major assessments, care being taken to minimize disturbance of both onion couch and the crop by working from the plot edge. The remaining area was used for destructive sampling.

Effect of straw burning, Assessment of the effect of straw burning on onion couch regrowth was made immediately before the herbicide treatments were applied (7 October 1975). Four plants were excavated from the destructive sampling area on both burnt and unburnt plots and counts made of the number of shoots, expanded and rolled leaves. These aerialparts were then dried for 24 h at 100°C and then weighed. Effect of herbicide treatment. All plants within the fixed square metre areas on each sub-sub-plot were excavated one year after application. After washing, shoots and bulbs were counted. The aerial parts were separated from the bulbs and both were dried for 24 h at 100°C and weighed. Due to a missed drill row, uneven growth occurred o n one replicate and statistical analysis was confined to the remaining two replicates.

Experiment 2 Treatment and design. The experiment was set up in a u t u m n 1979 on an area naturally infested with onion couch near Hindon, Wiltshire. A randomized block design was used with four replicates. Plots measured 5 × 3 m with a 1 m pathway between replicates and the whole experimental area measured 24 × 24 m. The previous crop of winter wheat was harvested on 4 September 1979, after which the plots were raked clear of straw. The first application of glyphosate was made on 25 September 1979 using a CO2-pressurized sprayer with a 3 m boom carried by two operators. Spraying Systems 6502 'Teejet' nozzles were used to

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apply 0"5, 1-0 or 1.5 kg a.e./ha of glyphosate at a spray volume of 225 f/ha and at a pressure of 210 kPa. The second application, to separate plots, was carried out on 12 October 1979 using the same equipment. The site was mouldboard ploughed to a depth of approximately 20 cm on 18 October 1979 and sown with winter wheat (cv. Maris Huntsman) on 19 October 1979. In the following spring a single dose of flamprop-methyl at 0,52 kg a.i./ha was applied on 9 May 1980 when the crop plants had one node detectable (stage 31; Zadoks, Chang and Konzak, 1974). The treatment was applied using the equipment described previously, but at a spray volume of 277 f/ha and pressure of 280 kPa. Growth stage assessments. At each application date, onion couch shoot numbers were counted in appropriate plots using one 60 × 60 cm quadrat per plot. In addition, a 60 × 60 cm area was excavated from each replicate for more detailed assessments to determine the numbers of bulbs and shoots, and shoot lengths. Effect of herbicide treatments. All treatment assessments were made in the central 1 × 1 m area of each plot. Pre-harvest inflorescence counts were made on 24 July 1980 using four 2 × 0'5 m quadrats per plot. The final assessment was carried out on 5 November 1980. The central assessment area on each plot was excavated and, after washing, shoots and bulbs were counted. The aerial parts were removed from the bulbs and both were dried for 24 h at 100°C and then weighed. Results Experiment 1 Effect of straw burning. Before herbicide application there were no visible differences in regrowth from pre-conditioning the foliage by straw burning, nor any reduction of either shoots or expanded and rolled leaves compared with plants which did not receive any straw-burning treatments (Table 1). Measurements from unsprayed plants 15 months after burning (Table 2) indicated an increase in growth, particularly of shoots, compared with unburnt plants. The results suggest also that herbicide performance was poorer following straw burning. In neither case did these differences achieve significance. Effect of herbicide. The main effects of herbicide and dose show marked differences between treatments in the numbers of shoots and bulbs (Table 2). Glyphosate at 1.0 and 1.5 kg a.e./ha gave the highest levels of control of both shoots and bulbs. Control of shoots and bulbs by aminotriazole at all doses was poor and at best equivalent to that achieved by the lowest dose of glyphosate. Dalapon was intermediate in effect between glyphosate and aminotriazole. This TABLE 1. Numbers of A. elatius ssp. bulbosum shoots, expanded leaves and rolled leaves/plant from burnt and unburnt plots, immediately before herbicide treatment Treatment

Shoots

-- Burning + Burning SE

34"5 37-3 +4"84

Expanded leaves 57,3 76.3 +8.69

Rolled leaves 16.3 14.5 +2.74

502 (21-9) 71 (7-9) 50 (5.5) 1077 (32.6) 1113 (33.2) 903 (30.0) 791 (27.9) 550 (23-5) 390 (19.8)

0.5 1.0 1.5 1-5 3.0 4.5 6.0 12.0 18.0 (2.21) (3.98)

(3.19)

Shoots

1374 (36.7)

470 (21.5) 58 (7.4) 30 (4.9) 794 (28.2) 680 (25.8) 716 (26.6) 564 (23.5) 565 (23.7) 316 (17.6)

- Burning

*Data transformed to x/~ + 1, in parentheses

1811 (42.5)

+ Burning

Dose (kg a.e. or a.i./ha)

2112 (45.9)

609 (23.9) 61 (7.0) 33 (4-6) 1142 (33.2) 1145 (33.2) 811 (28.5) 607 (23.7) 428 (20.7) 238 (15.2)

+ Burning

(3.03) (5.15)

(4"24)

Bulbs

Numbers of A. elatius ssp. bulbosum shoots and bulbs/m2 assessed one year after treatment*

SE of herbicide treatment means Unsprayed control SE of unsprayed control means SED between treatments and unsprayed

Dalapon

Aminotriazole

Glyphosate

Herbicide treatment

TABLE 2.

Burning

1833 (42.3)

553 (23-3) 65 (8.1) 20 (4.2) 1106 (33.1) 687 (26.2) 1026 (31.0) 580 (23.9) 484 (22.0) 269 (15.7)

-

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Effect of herbicides on onion couch

chemical appeared to have a greater effect on bulb numbers than on shoot numbers, especially at the higher doses. Experiment 2

On untreated plots shoot numbers, expanded leaves per shoot and shoots per bulb all appeared to increase between the first and second spray timings (Table 3). However, these increases were not statistically significant. Measurements of shoot length over this 17-day period indicated a slight increase in the proportion of shoots less than 100 mm in length and an overall decrease in mean length. Growth stage assessments.

TABLE 3. Details of growth stage characteristics of A. elatius ssp. bulbosum at two glyphosate application timings (experiment 2) Application date Characteristics

25 September 1979

Numbers of shoots/m2 Number of expanded leaves/shoot Number of shoots/bulb Mean shoot length (mm) Shoots < 100 mm in length (%)

12 October 1979 SE +

141 1.5 0.5 157.2 37.8

147 1.7 0.6 130-0 39-3

21.7 0.13 0.04 10-6

All treatments significantly reduced the number of inflorescences present in July (Table 4). Control from the lowest dose of glyphosate applied at the later timing (October) was poorer than that achieved from the highest dose applied at the same date and from the single application of Effect o f herbicide treatments.

TABLE 4. Numbers of A. elatius ssp. bulbosum inflorescence/m2, assessed in July 1980, and shoots and bulbs/m2 assessed in November 1980" Herbicide treatments Glyphosate Glyphosate Flampropmethyl Unsprayed control SE

Dose (kg a.e. or a.L/ha) 0.5 1-0 1.5 { 0-5 1-0 1.5 0.52

Application date 25 Sept. 1979

Inflorescence t }

12 Oct. 1979 9 May 1 9 8 0

2-2(1-8) 3.1(2.0) 1.8(1-6) 5-8(2.5) 0.9(1.3) 0.3(1.1) 0-3(1.1) 25-0(4.8)

Shoots 210(13.5) 122(9.1) 97(9.5) 385(19.6) 108(9.6) 67(7-5) 610(22.4)

Bulbs 337(16.7) 190(10-9) 130(10-7) 725(26.4) 126(10.6) 104(9.0) 1238(32.7)

1352(34-3) 2928(50-3)

+ (0.43) *Data transformedto x ~ + 1 in parenthesis

+ (4"02)

+ (5-55)

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flamprop-methyl. Both of the latter treatments gave 99~/o reduction of inflorescences. Both autumn applications ofglyphosate at 1.0 and 1.5 kg a.e./ha resulted in high levels of control of both shoots and bulbs with no significant difference between date of application. The control achieved at these doses was better than that achieved from flamprop-methyl although this treatment reduced the number of shoots and bulbs by 55~o and 58% respectively. Discussion The rate of onion couch regrowth following harvest shows marked differences at each site. The experiment conducted at Begbroke on the artificially established population indicates very slow shoot regrowth, taking over 60 days to reach the desired target height of 10-15 cm. In contrast, regrowth on t h e naturally occurring population reached this size within 21 days. This difference in growth rate between the two sites appears not to be related to moisture or temperature levels. Meteorological data (Table 5) recorded at sites within a 30 kan radius of the TABLE 5.

Total monthly rainfall (mm) and mean grass minimum temperatures (°C) Oxford (1975)

August September October

Meteorological site Boscombe Down (1979)

Rain

Grass rain.

Rain

Grass rain.

30"2 95"3 0.1

11"1 6"5 6.5

66"7 25.5 0"0

6"9 4"4 6"8

*Source: MeteorologicalOffice,Bracknell two experiments in 1975 and 1979 indicate that for August, September and October neither factor was limiting. Although other environmental factors cannot be ignored, it is unlikely that these alone would account for the differences in speed of regrowth between the two sites. Contrasting soil type, previous cultivation practice or cropping and harvest date may also have influenced regrowth. Birnie (1983) observed differences in onion couch regrowth after cereal harvest which suggested that slower regrowth occurred following spring barley: Variability in rate of autumn regrowth has considerable practical significance for herbicide effectiveness. It seems possible that the cases of poor control reported by field advisors have occurred when mixed populations have been sprayed, when regrowth of common couch was adequate whereas that of onion couch was not. The rate of shoot and leaf regrowth appeared to be largely unaffected by straw burning although the onset of growth was not recorded. Birnie (1983) also reported that burning did not influence markedly the rate of onion couch regrowth after winter wheat harvest. Although the effect of straw burning may not be apparent in the short term, later assessments suggest that it may eventually result in increased onion couch growth. This could lead to reduced herbicide activity but results from the Begbroke experiment do not show significant reductions in

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Effect of herbicides on onion couch

effectiveness, following straw burning, of glyphosate, aminotriazole or dalapon when measured one year after treatment. The lack of significance must be attributable in part to the reduced replication, although onion couch populations tend to be inherently variable. Although the use of an artificially established population reduces variability, standard errors are still high. Effective control with glyphosate appears to be achieved between the end of September and the middle of October. At Hindon there was little evidence to suggest that differences in regrowth between application timings were sufficient to affect the final degree of control, although it is conceivable that mouldboard ploughing may have masked any differences. The results from glyphosate applications suggest that, if shoot regrowth has reached a target height of 10-15 cm, then control of onion couch can be achieved where the recommended dose is applied. Comparison of shoot numbers shows good control when assessed 12-15 months after spraying but when related to the initial population, control is less satisfactory. Mouldboard ploughing, which has been shown to reduce shoot and bulb numbers (Ayres, 1977), does not appear to have been effective at Hindon and, in combination with glyphosate, this treatment might have been expected to give a greater reduction than was, in fact, achieved. The experiment conducted at Begbroke in undisturbed soil indicates that translocation of glyphosate is satisfactory provided that the bulb chains are joined and there is an adequate leaf target area. However, the experiment was conducted on an artificially established population with fragmented plants. In natural populations, bulbs are often aggregated and some bulbs may not be connected or the chain may be too long for.effective translocation. Evidence from Hindon shows that the number of shoots per bulb was less than one, and other data (Ayres, 1981) have also indicated that, with normal cultivations and naturally occurring infestations, a shoot-to-bulb ratio greater than one does not often occur. This low ratio of foliage area to numbers of bulbs does not appear to have affected the degree of translocation of glyphosate or the final level of control at Hindon. Control from both aminotriazole and dalapon at the dose rates used in this experiment was poor. Subsequent cultivations are usually required to achieve the best effect with these herbicides against common couch (Anonymous, 1977) and these results indicate that this may also be true for onion couch. Both herbicides are relatively persistent and can create considerable risks for a following crop sown in the autumn. Flamprop-methyl gave good suppression of onion couch inflorescences but limited control of shoots and bulbs. Although the numbers of both shoots and bulbs were reduced by the effects of the spring application of flamprop-methyl, the subsequent autumn regrowthdid not appear to be either delayed or inhibited. Thus the activity of autumn-applied herbicide treatments is unlikely to be affected by modification of onion couch regrowth from the use of flamprop-methyl in the spring. The results presented in this paper provide additional information to current recommendations for the control of onion couch in arable cropping systems. The experiments demonstrate that glyphosate at recommended rates can be effective against this weed in autumn cereal stubbles with or without additional cultivations, provided that there is adequate active regrowth. Further investigations into the effects of defoliation at harvest are desirable. The recently developed use of glyphosate applied pre-harvest to a standing cereal crop has

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extended the period o f treatment timing (O'Keeffe, 1980, 1981) but the results suggest that the control o f onion couch, although significant, may be Variable. Birnie (1983) also observed variable control with pre-harvest applications of glyphosate used for onion couch control and further work may be required to determine what factors are affecting herbicide performance. Acknowledgements I wish to thank M r G. W. Cussans for his help and advice and M r J. E. Allen o f Pertwood M a n o r Farm, H i n d o n who kindly provided the site. T h a n k s are due also to Miss J. E. Birnie and Messrs P. Bacon, J. A. Carrington, J-C. Cochet, R. A. P. D e n n e r and K. M. Irwin for their technical assistance.

References ANONYMOUS (1977). Couch. M A F F Advisory Leaflet 89. London: HMSO. AYRES, P. (1977). The growth of Arrhenatherum elatius var bulbosum (Willd.) Spenn. in spring barley, as influenced by cultivation. Weed Research 17, 423-428. AYRES, P. (1981). Investigations on the growth of Arrhenatherum elatius var bulbosum with reference to the effect of tillage, autumn regrowth and reproduction by seed. Association of Applied Biologists Conference. Grass Weeds in Cereals in the United Kingdom, pp. 77-81. AAB Office, NVRS, Wellesbourne, UK. BIRNIE, J.E. (1983). A preliminary study on the timing of glyphosate application for the control of onion couch. Tests of Agrochemicals and Cultivars; Annals of Applied Biology 103, Supplement 4, 108-109. EVANS, D.M. (1972). Field performance of glyphosate derivatives in the control of Agropyron repens and other perennial weeds. Proceedings I l th British Weed Control Conference, pp. 64-70. INGRAM, G.H. (1975). The distribution of perennial weed grasses in the arable regions of the U.K. Status, Biology and Control of Grassweeds in Europe, Proceedings European Weed Research Society Symposium held at Versailles, France, 2-3 December 1975,-pp. 14. Wageningen:

EWRS. O'KEEFFE, M.G. (1980). The control of Agropyron repens and broad-leaved weeds pre-harvest of wheat and barley with the isopropylamine salt of glyphosate. Proceedings 1980 British Crop Protection Conference--Weeds 1, 53-60. O'KEEFFE, M.G. (1981). The control of perennial grasses by pre-harvest applications of glyphosate. Association of Applied Biologists Conference. Grass Weeds in Cereals in the United Kingdom, 137,144. AAB Office, NVRS, Wellesbourne, UK. ZADOKS, J.C., CHANG, T.T. and KONZAK, C.F. (1974). A decimal code for the growth stages of cereals. Weed Research 14, 415-421. Accepted 25 October 1984