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Drainwater filtration for the control of nematodes in hydroponic-type systems
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Drainwater filtration for the control of nematodes in hydroponic-type systems M. M o e n s * a n d G. H e n d r i c k x
Rijksstation voor Nematologie en Entomologie, Burg. Van Gansberghelaan, 96, B-9820 Merelbeke, Belgium
Abstract
Keywords
Ornamental pot plants grown on hydroponic-type systems may be infected by nematodes distributed by the circulating nutrient solution. Laboratory and practical experiments demonstrate the usefulness of filtration techniques for effective nematode control. A filter unit was built in which the drainwater was caught in a sedimentation reservoir from which it was pumped (10001 h- 1) into a second tank, passing through a series of four filters comprising a gauze cartridge (150 lam) and three polyester felt filter bags (80, 1 and 1 lam). All the plant-parasitic nematodes were retained. Hyd roponic-type system; nematodes; drainwater; filtration
Introduction
Ornamental pot plants have an extended list of possible nematode pests (for reviews see Hague, 1972; Lamberti, 1981). In Belgium Aphelenchoides fragariae, Radopholus similis and thermophylic Meloidogyne spp. can be considered as the most economically important plant-parasitic nematodes attacking ornamentals. Leaf and bud nematodes can damage directly the parts of the plant above ground. Root nematode infections cause root damage which is reflected in a poorer plant growth with fewer, smaller and in some cases imperfect leaves. Besides the direct losses, plant-parasitic nematodes can cause export problems. In view of the general interest, this is even more important than the direct production losses. Ornamental pot plants are grown increasingly on hydroponic-type installations. In such systems nutrient solutions are circulated at intervals to the pot base. The water that is not taken up by the plant substrate drains to a reservoir from which it is redistributed over the entire system. Ornamental pot plants are mainly propagated by vegetative multiplication. In this way, endoparasitic root nematodes can easily be spread over a great number of plants. Infected plants, by liberating nematodes into the circulating nutrient solution, constitute the primary infection source in hydroponic-type systems. Laboratory experiments have shown that nematodes circulating within the nutrient solution are capable of infecting pot plants situated downstream in the gullies (Moens and Hendrickx, 1990). Marantaceae plants propagated in vitro and irrigated in this way in commercial greenhouses became infected with Radopholus similis. *To whom correspondence should be addressed
The incorporation of pesticides in the nutrient solution is attractive as a disease or pest control technique. On the one hand this method is time saving; on the other, it offers the possibility of using reduced quantities of chemicals. Aphids (Dunne and Donovan, 1977) and some diseases (Staunton and Cormican, 1980; Jamart, De Prest and Kamoen, 1988) are successfully controlled in this way. Earlier work has shown that chemical control of Radopholus similis in Marantaceae by means of oxamyl is unsuccessful (Hendrickx, Coolen and Moens, 1986). Laboratory experiments involving ultraviolet irradiation of nematode-contaminated water have given very promising results (Moens and Hendrickx, 1989). Some minerals (e.g. manganese and magnesium), however, are unstable in these conditions and precipitate, causing nutrient deficiencies. For this reason various filters and filtration techniques have been tested in order to control nematodes in the drainwater and to protect plants from infection.
Materials and methods L a b o r a t o r y tests
The nematode-retention ability of a set of filter cartridges, filter bags, filter membranes and other filtration equipment (Tablel) was tested in the laboratory. Except for the membrane filtration, the tests were performed with a nematode suspension of ~ 500 000 freshly hatched Globodera rostochiensis second-stage juveniles in 2001 wellwater. The total quantity was pumped through the test filtration element at a constant flow rate (6001 h - 1) and at a differential pressure of 0 Pa at the start of the test. The individual tests took 20 minutes. The filtrate was caught and processed in a continuous centrifuge (CEPA laboratory centrifuge 9700g; 361h-1) equipped with a serum-
0261-2194/92/01/0069-05 © 1992 Butterworth-Heinemann Ltd CROP PROTECTION Vol. 11 February 1992
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Nematode control in drainwater by filtration: M. Moens and G. Hendrickx
Table 1. Laboratory efficiency of filtration elements Mean percentage Filtration element Wound polypropylene fibre cartridge with double open end
Pore size (tam) ~
G. rostochiensis (J2) h
recovered in the filtrate
1 5
10
Wound polypropylene fibre cartridge with end caps Polypropylene filtermedium cartridge thermally sealed to polypropylene ends
Non-woven polypropylene filtermediumcartridge Ceramic filter candle Diatomite filter unit Polyester felt filter bag
0.30 (0.09)' 2.00 (0.03) 6.00 (0.60) 0.00 (0.00)
0.5 1 3
0.00 (0.00) 0.00 (0.00) 0.00 (0.00)
5 10 25 1.2
0.01 (0.00) 0.04 (0.01) 0.| 1 (0.03) 0.00 (0.00)
-1
0.00 (0.00) 9.50 (4.35) 0.10 (0.02)
"Information from supplier; ~second-stagejuveniles; 's.d. in parentheses
separating cylinder with a bottom valve. In this way, nematodes present in the filtrate were concentrated in ~ 200 ml water ready for counting. The total volume was examined for nematodes; no subsamples were taken. Filter membranes were tested using an Amafilter crossflow cell, type TPA 090 (flow rate 90-1801 h - 1, differential pressure 460-440 kPa). Eggs, juveniles and adult stages of Pratylenchus crenatus, and second-stage juveniles of G. rostochiensis and M. incognita, suspended in 101 well-water, served as test organisms. During the cross-flow tests the residue, i.e. the part of the suspension that does not pass through the filter, was retained. The test took 7-14 minutes. The nematode presence in the filtrate was evaluated as described above. The laboratory tests were conducted separately with three different units of the same filtration element.
Glasshouse tests This type of research, conducted in a commercial greenhouse, involved only those filtration elements that had shown promise in laboratory conditions. Cross-flow filtration was not tested under these conditions as a special installation would have been necessary. The tests were conducted at two flow rates: 6001 h 1 in the experiments with individually mounted cartridges and cartridge filtration systems, and 10001h-1 in the tests of filter-bag filtration systems. These tests differed in two respects from the conditions in the laboratory: starting at an initial pressure of 0 Pa, the practical tests took place at increasing pressure (owing to a build-up of dirt on the filters); in addition, other nematodes were present in the drainwater, Meloidogyne incognita, Radopholus similis and the nonplant-parasitic nematodes Butlerius degrissei and Pristionchus lheritieri being found in variable numbers. Their presence in the drainwater (per 1001) varied as follows: Meloidogyne incognita, 60 3870 (mean 780) individuals;
CROP PROTECTION Vol. 11 February 1992
Radopholus similis, 30 400 (mean 160) individuals, and the sum of Butlerius degrissei and Pristionchus lheritieri 270 2800 (mean 1500) individuals. Because of this changing nematode presence, the nematode contents of both the filtered drainwater and the untreated drainwater sampled immediately before the tests were compared. The nematodes present in the samples were concentrated for counting by centrifuging in a continuous laboratory centrifuge (see 'Laboratory tests'). For individually mounted filters this procedure was repeated three times. The tests with filtration systems were not repeated but samples were taken at various times after they came into use.
Results
Laboratory experiments The results of the laboratory screening tests are presented in Table 1. Among the cartridges tested, two have been examined at different pore sizes. It is obvious that the nematode-retaining efficiency is dependent on pore size. None of the tested cartridges comprising wound polypropylene fibres and with double open ends ( A M F - C U N O ) removed all the nematodes present in the suspension. Polypropylene depth 'filtermedium' cartridges thermally sealed on to polypropylene ends (Millipore Polygard-CR) were effective from pore size 3 lam downward. However, only small quantities of nematodes passed through cartridges with larger pores. Cartridges composed of wound polypropylene fibres and with end caps (Millipore Rogard) and the polypropylene filtermedium cartridges (Millipore Polygard-CN) completely retained the nematodes. Owing to their special fitting, ceramic 'candles' (Katadyn no. 4) had to be tested in an adapted cartridge housing holding three candles. In these circumstances the flow rate was limited to 5001 h 1 and the differential pressure raised to 400 kPA, because of the rapid clogging of the filter by insoluble ferric hydroxide formed after oxidation of the ferric bicarbonate present in the well-water used (iron content 0.6 mg 1- 1). The filtrate, however, was nematode free. Diatoms, frequently used in water treatment plants, were tested with a filter unit in which the diatoms adhered by suction to a 30 ~tm nylon gauze. The efficiency was very poor: on average, 9.5% of the nematodes passed through the gauze and a considerable amount of diatoms remained in the filtrate. The mean percentage of nematodes recovered in the filtrate of polyester felt filter bags (GAF) was 0.1%. The nematode content of water filtered with the crossflow unit was largely dependent on the pore size of the membrane: 10 ~tm membranes (AMA) retained the bulk of the suspended nematodes, but the smaller the nematode size, the greater the quantity of nematodes recovered from the permeate. Thus, the permeate was free from adults and eggs of P. crenatus; the proportion of small juveniles of P. crenatus and second-stage juveniles of G. rostochiensis and M. incognita was respectively 6.9 ( ± 0.4), 1.7 ( + 0.2) and
N e m a t o d e control in d r a i n w a t e r by filtration: M. Moens and G. Hendrickx
71
Table 2. Nematode retention by four cartridge filtration systems and build-up of differential pressure over the end filter cartridge
Percentage nematode retention after end filter Filtration system"
150-25-3 pm MDE cartridges
150-25 1 ~m M D E cartridges 150 25 0.51am M D E c a r t r i d g e s
150-25 ~tm M D E cartridges 1.2 I-tm ME cartridge
Filtered v o l u m e (m 3)
Differential p r e s s u r e over end cartridge ( × 100 k P a )
0.15 0.60 [.20 1.35
' 0.5 2.3 3.0
0.15 32.00
M. incognita
R. similis
Other b
100.0
100.0 --
-97.5
100.0 --100.0 100.0 99.1
100.0 97.0
96.0
1.0
100.0 98.6
0.15
--
100.0
I00.0
100.0
9.00 30.00
0.0 [ .0
100.0 99.2
100.0 --
98.0 97.0
0.60 2.40
1.0 1.8
100.0 100.0
100.0 100.0
100.0 100.0
"MDE: polypropylene depth filterm,edium cartridges thermally sealed to polypropylene ends; ME: polypropylene filtermedium cartridges; hButlerius degrissei and Pristionchus lheritieri: 'not observed
3.5 ( + 0.2) of the number present in untreated water. From pore size 5 ~tm down, all the nematodes were retained.
G l a s s h o u s e tests
The practical experiments were restricted to wound polypropylene fibre cartridges with end caps (WFE), polypropylene depth filtermedium cartridges thermally sealed to polypropylene ends (MDE), polypropylene filtermedium cartridges (ME), and polyester felt filter bags.
Individually mounted cartridges.
The differential pressure over individually mounted WFE-cartridges increased to 15 25 kPa after filtration of 6 m 3 drainwater; after 29 m 3 the pressure increased to l l0 130kPa. At that stage the filtrate contained an average percentage of 1.3 ( + 0.7), 0.0 (+0.0), and 2.5 (+0.8) of, respectively, Meloidogyne second-stage juveniles, R. similis individuals, and the nonplant-parasitic nematodes present in the drainwater. The M D E cartridges, which retained all the nematodes under laboratory conditions, remained very efficient in practical circumstances as long as the differential pressure remained equal to zero. Owing to the dirt deposited on the cartridges, however, the pressure increased quickly to 200 kPa. After filtration of 30 m 3, the mean percentage nematode content of the filtrate was 1 (+0.7) (0.5~tm cartridge) to 4.1% ( + 3.1) (3 I.tm cartridge) of the total amount of nematodes present in the drainwater. Total retention of the nematodes, even at high differential pressure (400kPa) was obtained with 1.2~tm ME cartridges.
Cartridge filtration systems. As an increase in the differential pressure over the filter cartridge results in an increase in the number of nematodes in the filtrate, deposition of dirt on the cartridge must be prevented as long as possible by means of adequate prefiltration. Three filtration systems were tested in practical conditions. The drainwater was pumped over four successive filter cartridges: a metal
gauze filter (150~tm) and an M D E cartridge (251am) as prefiltration elements, and alternately a 3 lain, a 1 ~tm or a 0.5 lam M D E cartridge as end filter. The change of pressure and the nematode-retaining capacity after different volumes of drainwater have been filtered are shown in
Table 2. The rapid increase in pressure registered over the end filter (3 ~tm) of the first filtration system was due to the presence in the drainwater of the insoluble fungicide metalaxyl. For this reason complete obstruction of this system was observed 150 rain after the start of filtration. In both of the other M D E filtration systems the pressure was limited to 100kPA, even after filtration of 3 0 - 3 2 m 3 drainwater. Observations 15min after the start of the filtration showed that, at that stage, nematode retention is complete with the three M D E filter systems tested. As a consequence of the increase in pressure with increasing volume, a small fraction of the nematodes pass through the last filter cartridge. Complete retention, however, even at high differential pressure, is obtained with a cartridge filtration system using a 1.2 ~tm ME cartridge as endfilter. After the filtration of 3 m 3 drainwater, however, this system becomes completely obstructed (differential pressure, 400 kPa).
Filter bag filtration system.
In practical conditions filter bags were not tested separately but assembled in a filtration system. The drainwater was pumped over, successively, a metal gauze filter (150 ~tm) and three polyester felt filter bags (80, 1 and 1 ~tm). The results, summarized in Table 3, indicate that drainwater dirt was retained by the first 1 Jam filter bag, resulting in an increase of the differential pressure over this filter. As a consequence, the end filtration over the second 1 ~tm filter bag took place under optimal conditions. No plant-parasitic nematodes were found in the filtrate of the first 1 ~m filter bag, even after filtration of 30 m 3. Only a fraction of the smaller nonplant-parasitic nematodes present in the drainwater was found. This fraction consisted of second-stage juveniles of Pristionchus lheritieri, which differed markedly in size from
CROP PROTECTIONVol. 11 February 1992
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N e m a t o d e control in d r a i n w a t e r by filtration: M. M o e n s and G. H e n d r i c k x
Table3. Build-up of differential pressure over polyester felt filter bags mounted in a filtration system and percentage nematodes retained by individual filters
Percentage nematode retention Filter bag pore size (gm)
Differential pressure ( x 1O0kPa)
M. incognita
R. similis
Non-plantparasitic nematodes
0.25
80 !
0.0 1.5
0.0 100.0
0.0 lOO.O
0.0 98.8
l
0.0
100.0
100.0
2.60
80 1
0.0 2.0
0.0 100.0
0.0 100.0
1
0.0
100.0
100.0
30.1)0
80 l I
0.0 3.75 0.0
0.0 100.0 100.0
0.0 100.0 100.0
Filtered volume (m 3)
the plant-parasitic nematodes present in the nutrient solution (length, 2 3 4 ~ 9 0 lam; width, 14 17 ~tm; Geraert, 1983). Their retention by the filter bags increased with increasing dirt deposition.
Discussion The most logical, attractive and easiest way to clean water is filtration. Previous laboratory studies on the removal of motile and non-motile nematodes by rapid sand filters have shown that between 55-60% (Seth et al., 1968) and 75% (Peterson, Engelbrecht and Austin, 1965) of the nematodes will pass through. Wei, Engelbrecht and Austin (1965) observed that most motile nematodes eventually penetrate the filter beds, although they may be retained temporarily during the early stages of filtration. Motile nematodes appear to dislodge a significant fraction of the non-motile ones initially held back. When all the nematodes in the influent are dead, most of them are retained 96% according to Wei et al. (1969) or 98% according to Peterson et al. (1965). To satisfy the requirements of drainwater filtration the filter unit must conform to the following criteria: (1) it must achieve 100% retention of plant-parasitic nematodes, even at high pressures; (2) it must be reliable, i.e. the result must be reproducible; (3) it should be easy to instal and to remove; (4) it should be adapted for discontinuous use; (5) it should be usable at different flow rates; (6) it should have a relatively long lffespan and (7) it should be relatively inexpensive. On the basis of at least one of these criteria, the diatomic filter, the ceramic filter, the M E cartridges, the wound polypropylene fibre cartridges with end caps and the wound polypropylene fibre cartridges with double open ends failed the tests. With regard to nematode retention, promising results were obtained with the crossflow filtration technique; such a system, however, is very expensive. Almost total retention of the plant-parasitic nematodes present was achieved with a filtration system composed of M D E cartridges. A filter unit composed of polyester felt filter bags retained all the plant-parasitic nematodes.
CROP PROTECTION Vol. 11 F e b r u a r y 1992
100.0
0.0 32.0 85.0 0.0 79.2 99.2
The lifespan of such filter units is primarily determined by the concentration of solids in the drainwater. As this concentration differs among production plants, but also varies according to the season, the lifespan is difficult to predict. The I p,m filter bags, incorporated into the irrigation system of a commercial greenhouse, needed replacement only after 140 m 3 water had passed through. In hydroponic-type systems the irrigation water is supplied at a high flow rate. Filtration of this total volume of water would require a high-capacity filtration system. As plant-parasitic nematodes are present only in drainwater there is no need for such a system. As the returning drainwater is not under pressure, direct filtration is excluded. A system has therefore been developed in which the drainwater is caught in an initial reservoir from which it is pumped (10001h 1) into a second tank ( F i g u r e l ) , passing four filters (a 150~tm metal gauze cartridge and three polyester felt filter bags (80, 1 and 1 gin). Collection of the water in an initial reservoir offers two advantages. On the one hand the nematodes are able to sediment, resulting in a considerable reduction of the suspended nematodes. This technique is also used in drinking-water plants and results in a significant reduction of the nematode concentration (Murad and Bazer, 1970; Mott, Mulamoottil and Harrison, 1981). On the other hand it enables the filtration flow rate to be uncoupled from the flow rate of the drainwater; this makes it possible to use a small-capacity filtration system working at low differential pressure. Problems with insoluble pesticides are less frequent in this system. Filtration of the drainwater of hydroponic-type systems, combined with the use of micropropagated plants and the Drainwater
li
Filter unit
To the greenhouse
ii!ifi
Figure 1. System for filtering nematodes out of drainwater, independent of the flow rate of the returning water
Nematode control in drainwater by filtration: M. Moens and G. Hendrickx use o f a n e m a t o d e - f r e e s u b s t r a t e m a k e s t h e p r o d u c t i o n o f n e m a t o d e - f r e e o r n a m e n t a l p o t p l a n t s m o r e likely.
Acknowledgements T h e a u t h o r s a r e g r a t e f u l to R e n a a t M o e r m a n s o f t h e Biometric Unit of the Agricultural Research Centre Ghent f o r his a d v i c e a n d to M a g d a V a n d e p u t t e a n d L u c r 6 c e Matthys for their technical assistance.
73
Lamberti, F. (198l) Plant nematode problems in the Mediterranean region. Helminthol. Abstr. Ser. B, Plant Nematol. 50, 145-166 Moens, M. and Hendrickx, G. (1989) Sensitivity of Meloidogyne incognita second stage juveniles to UV-irradiation. Meded. Fac. Landb Wetensch. R~jksuniv. Gent 54, 1187 1193 Moens, M. and Hendriekx, G. (1990) Nematode infection by recirculating nutrient solutions in gullies. Meded. Fac. Landb Wetensch. R~/ksuniv. Gent 55, 739 744 Mott, J. B., Mulamoottil, G. and Harrison, A. D. (1981) A 13-month survey of the nematodes at three water treatment plants in Southern Ontario, Canada. Water Res. 15, 729 738 Murad, 3. L. and Bazer, G. T. (1970) Diplogasterid and rhabditid nematodes in a wastewater treatment plant and factors related to their dispersal. J. Water Pollution Control Fed. 42, 106-114
References Dunne, R. and Donovan, M. (1!)77) Aphid control on tomatoes in a hydroponic system. Acta Hort. 82, 137 139
Peterson, R. L., Engelbreeht, R. S. and Austin, J. H. (1965) Freeliving Nematode Removal by Rapid Sand Filters. Paper presented at the National Symposium on Sanitary Engineering Research Development and Design, 27-30 July 1965, The Pennsylvania State University, University Park, PA
Hague, N. G. M. (1972) Nematode diseases of ftower bulbs, glasshouse crops and ornamentals. In: Economic Nematology (Ed. by J. M. Webster) pp. 409-434, Academic Press, London, New York
Seth, A. K., George, M. G., Bewtra, J. K. and Sharma, V. P. (1968) Nematode removal by rapid sand filtration. J. Am. Water Works Ass. 60, 962-968
Hendrickx, G. J., Coolen, W.A. and Moens, M.G. (1986) Search for Radopholus-free Calathea makoyana. Meded. Fac. LandbWetensch. Rijksuniv. Gent 51, 1325-1329
Staunton, W. P. and Cormican, T. P. (1980) The effects of pathogens and fungicides on tomatoes in a hydroponic system. Acta Hort. 98, 293-315
Geraert, E. (1983) Morphology and morphometry of Mesodiplogaster pseudolheritieri n.sp. (Nematcda: Rhabditida). Nematologica 29, 284 297 Jamart, G., De Prest, G. and Kamoen, O. (l 988) Control of Pythium spp. on ornamental plants in a nutrient-film system. Meded. Fac. LandbWetensch. Rijksuniv. Gent 53, 625-634
Wei, 1. W. T., Engelbreeht, R. S. and Austin, J. H. (1969) Removal of nematodes by rapid sand filtration. J. Sanit. Engng Div. Am. Soc. Civil Eng. 95, Proc. Paper 6384, 1 16 Received 8 April 1991 Revised 29 June 1991 Accepted 3 July 1991
CROP PROTECTION Vol. 11 February 1992
Drainwater filtration for the control of nematodes in hydroponic-type systems M. M o e n s * a n d G. H e n d r i c k x
Rijksstation voor Nematologie en Entomologie, Burg. Van Gansberghelaan, 96, B-9820 Merelbeke, Belgium
Abstract
Keywords
Ornamental pot plants grown on hydroponic-type systems may be infected by nematodes distributed by the circulating nutrient solution. Laboratory and practical experiments demonstrate the usefulness of filtration techniques for effective nematode control. A filter unit was built in which the drainwater was caught in a sedimentation reservoir from which it was pumped (10001 h- 1) into a second tank, passing through a series of four filters comprising a gauze cartridge (150 lam) and three polyester felt filter bags (80, 1 and 1 lam). All the plant-parasitic nematodes were retained. Hyd roponic-type system; nematodes; drainwater; filtration
Introduction
Ornamental pot plants have an extended list of possible nematode pests (for reviews see Hague, 1972; Lamberti, 1981). In Belgium Aphelenchoides fragariae, Radopholus similis and thermophylic Meloidogyne spp. can be considered as the most economically important plant-parasitic nematodes attacking ornamentals. Leaf and bud nematodes can damage directly the parts of the plant above ground. Root nematode infections cause root damage which is reflected in a poorer plant growth with fewer, smaller and in some cases imperfect leaves. Besides the direct losses, plant-parasitic nematodes can cause export problems. In view of the general interest, this is even more important than the direct production losses. Ornamental pot plants are grown increasingly on hydroponic-type installations. In such systems nutrient solutions are circulated at intervals to the pot base. The water that is not taken up by the plant substrate drains to a reservoir from which it is redistributed over the entire system. Ornamental pot plants are mainly propagated by vegetative multiplication. In this way, endoparasitic root nematodes can easily be spread over a great number of plants. Infected plants, by liberating nematodes into the circulating nutrient solution, constitute the primary infection source in hydroponic-type systems. Laboratory experiments have shown that nematodes circulating within the nutrient solution are capable of infecting pot plants situated downstream in the gullies (Moens and Hendrickx, 1990). Marantaceae plants propagated in vitro and irrigated in this way in commercial greenhouses became infected with Radopholus similis. *To whom correspondence should be addressed
The incorporation of pesticides in the nutrient solution is attractive as a disease or pest control technique. On the one hand this method is time saving; on the other, it offers the possibility of using reduced quantities of chemicals. Aphids (Dunne and Donovan, 1977) and some diseases (Staunton and Cormican, 1980; Jamart, De Prest and Kamoen, 1988) are successfully controlled in this way. Earlier work has shown that chemical control of Radopholus similis in Marantaceae by means of oxamyl is unsuccessful (Hendrickx, Coolen and Moens, 1986). Laboratory experiments involving ultraviolet irradiation of nematode-contaminated water have given very promising results (Moens and Hendrickx, 1989). Some minerals (e.g. manganese and magnesium), however, are unstable in these conditions and precipitate, causing nutrient deficiencies. For this reason various filters and filtration techniques have been tested in order to control nematodes in the drainwater and to protect plants from infection.
Materials and methods L a b o r a t o r y tests
The nematode-retention ability of a set of filter cartridges, filter bags, filter membranes and other filtration equipment (Tablel) was tested in the laboratory. Except for the membrane filtration, the tests were performed with a nematode suspension of ~ 500 000 freshly hatched Globodera rostochiensis second-stage juveniles in 2001 wellwater. The total quantity was pumped through the test filtration element at a constant flow rate (6001 h - 1) and at a differential pressure of 0 Pa at the start of the test. The individual tests took 20 minutes. The filtrate was caught and processed in a continuous centrifuge (CEPA laboratory centrifuge 9700g; 361h-1) equipped with a serum-
0261-2194/92/01/0069-05 © 1992 Butterworth-Heinemann Ltd CROP PROTECTION Vol. 11 February 1992
70
Nematode control in drainwater by filtration: M. Moens and G. Hendrickx
Table 1. Laboratory efficiency of filtration elements Mean percentage Filtration element Wound polypropylene fibre cartridge with double open end
Pore size (tam) ~
G. rostochiensis (J2) h
recovered in the filtrate
1 5
10
Wound polypropylene fibre cartridge with end caps Polypropylene filtermedium cartridge thermally sealed to polypropylene ends
Non-woven polypropylene filtermediumcartridge Ceramic filter candle Diatomite filter unit Polyester felt filter bag
0.30 (0.09)' 2.00 (0.03) 6.00 (0.60) 0.00 (0.00)
0.5 1 3
0.00 (0.00) 0.00 (0.00) 0.00 (0.00)
5 10 25 1.2
0.01 (0.00) 0.04 (0.01) 0.| 1 (0.03) 0.00 (0.00)
-1
0.00 (0.00) 9.50 (4.35) 0.10 (0.02)
"Information from supplier; ~second-stagejuveniles; 's.d. in parentheses
separating cylinder with a bottom valve. In this way, nematodes present in the filtrate were concentrated in ~ 200 ml water ready for counting. The total volume was examined for nematodes; no subsamples were taken. Filter membranes were tested using an Amafilter crossflow cell, type TPA 090 (flow rate 90-1801 h - 1, differential pressure 460-440 kPa). Eggs, juveniles and adult stages of Pratylenchus crenatus, and second-stage juveniles of G. rostochiensis and M. incognita, suspended in 101 well-water, served as test organisms. During the cross-flow tests the residue, i.e. the part of the suspension that does not pass through the filter, was retained. The test took 7-14 minutes. The nematode presence in the filtrate was evaluated as described above. The laboratory tests were conducted separately with three different units of the same filtration element.
Glasshouse tests This type of research, conducted in a commercial greenhouse, involved only those filtration elements that had shown promise in laboratory conditions. Cross-flow filtration was not tested under these conditions as a special installation would have been necessary. The tests were conducted at two flow rates: 6001 h 1 in the experiments with individually mounted cartridges and cartridge filtration systems, and 10001h-1 in the tests of filter-bag filtration systems. These tests differed in two respects from the conditions in the laboratory: starting at an initial pressure of 0 Pa, the practical tests took place at increasing pressure (owing to a build-up of dirt on the filters); in addition, other nematodes were present in the drainwater, Meloidogyne incognita, Radopholus similis and the nonplant-parasitic nematodes Butlerius degrissei and Pristionchus lheritieri being found in variable numbers. Their presence in the drainwater (per 1001) varied as follows: Meloidogyne incognita, 60 3870 (mean 780) individuals;
CROP PROTECTION Vol. 11 February 1992
Radopholus similis, 30 400 (mean 160) individuals, and the sum of Butlerius degrissei and Pristionchus lheritieri 270 2800 (mean 1500) individuals. Because of this changing nematode presence, the nematode contents of both the filtered drainwater and the untreated drainwater sampled immediately before the tests were compared. The nematodes present in the samples were concentrated for counting by centrifuging in a continuous laboratory centrifuge (see 'Laboratory tests'). For individually mounted filters this procedure was repeated three times. The tests with filtration systems were not repeated but samples were taken at various times after they came into use.
Results
Laboratory experiments The results of the laboratory screening tests are presented in Table 1. Among the cartridges tested, two have been examined at different pore sizes. It is obvious that the nematode-retaining efficiency is dependent on pore size. None of the tested cartridges comprising wound polypropylene fibres and with double open ends ( A M F - C U N O ) removed all the nematodes present in the suspension. Polypropylene depth 'filtermedium' cartridges thermally sealed on to polypropylene ends (Millipore Polygard-CR) were effective from pore size 3 lam downward. However, only small quantities of nematodes passed through cartridges with larger pores. Cartridges composed of wound polypropylene fibres and with end caps (Millipore Rogard) and the polypropylene filtermedium cartridges (Millipore Polygard-CN) completely retained the nematodes. Owing to their special fitting, ceramic 'candles' (Katadyn no. 4) had to be tested in an adapted cartridge housing holding three candles. In these circumstances the flow rate was limited to 5001 h 1 and the differential pressure raised to 400 kPA, because of the rapid clogging of the filter by insoluble ferric hydroxide formed after oxidation of the ferric bicarbonate present in the well-water used (iron content 0.6 mg 1- 1). The filtrate, however, was nematode free. Diatoms, frequently used in water treatment plants, were tested with a filter unit in which the diatoms adhered by suction to a 30 ~tm nylon gauze. The efficiency was very poor: on average, 9.5% of the nematodes passed through the gauze and a considerable amount of diatoms remained in the filtrate. The mean percentage of nematodes recovered in the filtrate of polyester felt filter bags (GAF) was 0.1%. The nematode content of water filtered with the crossflow unit was largely dependent on the pore size of the membrane: 10 ~tm membranes (AMA) retained the bulk of the suspended nematodes, but the smaller the nematode size, the greater the quantity of nematodes recovered from the permeate. Thus, the permeate was free from adults and eggs of P. crenatus; the proportion of small juveniles of P. crenatus and second-stage juveniles of G. rostochiensis and M. incognita was respectively 6.9 ( ± 0.4), 1.7 ( + 0.2) and
N e m a t o d e control in d r a i n w a t e r by filtration: M. Moens and G. Hendrickx
71
Table 2. Nematode retention by four cartridge filtration systems and build-up of differential pressure over the end filter cartridge
Percentage nematode retention after end filter Filtration system"
150-25-3 pm MDE cartridges
150-25 1 ~m M D E cartridges 150 25 0.51am M D E c a r t r i d g e s
150-25 ~tm M D E cartridges 1.2 I-tm ME cartridge
Filtered v o l u m e (m 3)
Differential p r e s s u r e over end cartridge ( × 100 k P a )
0.15 0.60 [.20 1.35
' 0.5 2.3 3.0
0.15 32.00
M. incognita
R. similis
Other b
100.0
100.0 --
-97.5
100.0 --100.0 100.0 99.1
100.0 97.0
96.0
1.0
100.0 98.6
0.15
--
100.0
I00.0
100.0
9.00 30.00
0.0 [ .0
100.0 99.2
100.0 --
98.0 97.0
0.60 2.40
1.0 1.8
100.0 100.0
100.0 100.0
100.0 100.0
"MDE: polypropylene depth filterm,edium cartridges thermally sealed to polypropylene ends; ME: polypropylene filtermedium cartridges; hButlerius degrissei and Pristionchus lheritieri: 'not observed
3.5 ( + 0.2) of the number present in untreated water. From pore size 5 ~tm down, all the nematodes were retained.
G l a s s h o u s e tests
The practical experiments were restricted to wound polypropylene fibre cartridges with end caps (WFE), polypropylene depth filtermedium cartridges thermally sealed to polypropylene ends (MDE), polypropylene filtermedium cartridges (ME), and polyester felt filter bags.
Individually mounted cartridges.
The differential pressure over individually mounted WFE-cartridges increased to 15 25 kPa after filtration of 6 m 3 drainwater; after 29 m 3 the pressure increased to l l0 130kPa. At that stage the filtrate contained an average percentage of 1.3 ( + 0.7), 0.0 (+0.0), and 2.5 (+0.8) of, respectively, Meloidogyne second-stage juveniles, R. similis individuals, and the nonplant-parasitic nematodes present in the drainwater. The M D E cartridges, which retained all the nematodes under laboratory conditions, remained very efficient in practical circumstances as long as the differential pressure remained equal to zero. Owing to the dirt deposited on the cartridges, however, the pressure increased quickly to 200 kPa. After filtration of 30 m 3, the mean percentage nematode content of the filtrate was 1 (+0.7) (0.5~tm cartridge) to 4.1% ( + 3.1) (3 I.tm cartridge) of the total amount of nematodes present in the drainwater. Total retention of the nematodes, even at high differential pressure (400kPa) was obtained with 1.2~tm ME cartridges.
Cartridge filtration systems. As an increase in the differential pressure over the filter cartridge results in an increase in the number of nematodes in the filtrate, deposition of dirt on the cartridge must be prevented as long as possible by means of adequate prefiltration. Three filtration systems were tested in practical conditions. The drainwater was pumped over four successive filter cartridges: a metal
gauze filter (150~tm) and an M D E cartridge (251am) as prefiltration elements, and alternately a 3 lain, a 1 ~tm or a 0.5 lam M D E cartridge as end filter. The change of pressure and the nematode-retaining capacity after different volumes of drainwater have been filtered are shown in
Table 2. The rapid increase in pressure registered over the end filter (3 ~tm) of the first filtration system was due to the presence in the drainwater of the insoluble fungicide metalaxyl. For this reason complete obstruction of this system was observed 150 rain after the start of filtration. In both of the other M D E filtration systems the pressure was limited to 100kPA, even after filtration of 3 0 - 3 2 m 3 drainwater. Observations 15min after the start of the filtration showed that, at that stage, nematode retention is complete with the three M D E filter systems tested. As a consequence of the increase in pressure with increasing volume, a small fraction of the nematodes pass through the last filter cartridge. Complete retention, however, even at high differential pressure, is obtained with a cartridge filtration system using a 1.2 ~tm ME cartridge as endfilter. After the filtration of 3 m 3 drainwater, however, this system becomes completely obstructed (differential pressure, 400 kPa).
Filter bag filtration system.
In practical conditions filter bags were not tested separately but assembled in a filtration system. The drainwater was pumped over, successively, a metal gauze filter (150 ~tm) and three polyester felt filter bags (80, 1 and 1 ~tm). The results, summarized in Table 3, indicate that drainwater dirt was retained by the first 1 Jam filter bag, resulting in an increase of the differential pressure over this filter. As a consequence, the end filtration over the second 1 ~tm filter bag took place under optimal conditions. No plant-parasitic nematodes were found in the filtrate of the first 1 ~m filter bag, even after filtration of 30 m 3. Only a fraction of the smaller nonplant-parasitic nematodes present in the drainwater was found. This fraction consisted of second-stage juveniles of Pristionchus lheritieri, which differed markedly in size from
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72
N e m a t o d e control in d r a i n w a t e r by filtration: M. M o e n s and G. H e n d r i c k x
Table3. Build-up of differential pressure over polyester felt filter bags mounted in a filtration system and percentage nematodes retained by individual filters
Percentage nematode retention Filter bag pore size (gm)
Differential pressure ( x 1O0kPa)
M. incognita
R. similis
Non-plantparasitic nematodes
0.25
80 !
0.0 1.5
0.0 100.0
0.0 lOO.O
0.0 98.8
l
0.0
100.0
100.0
2.60
80 1
0.0 2.0
0.0 100.0
0.0 100.0
1
0.0
100.0
100.0
30.1)0
80 l I
0.0 3.75 0.0
0.0 100.0 100.0
0.0 100.0 100.0
Filtered volume (m 3)
the plant-parasitic nematodes present in the nutrient solution (length, 2 3 4 ~ 9 0 lam; width, 14 17 ~tm; Geraert, 1983). Their retention by the filter bags increased with increasing dirt deposition.
Discussion The most logical, attractive and easiest way to clean water is filtration. Previous laboratory studies on the removal of motile and non-motile nematodes by rapid sand filters have shown that between 55-60% (Seth et al., 1968) and 75% (Peterson, Engelbrecht and Austin, 1965) of the nematodes will pass through. Wei, Engelbrecht and Austin (1965) observed that most motile nematodes eventually penetrate the filter beds, although they may be retained temporarily during the early stages of filtration. Motile nematodes appear to dislodge a significant fraction of the non-motile ones initially held back. When all the nematodes in the influent are dead, most of them are retained 96% according to Wei et al. (1969) or 98% according to Peterson et al. (1965). To satisfy the requirements of drainwater filtration the filter unit must conform to the following criteria: (1) it must achieve 100% retention of plant-parasitic nematodes, even at high pressures; (2) it must be reliable, i.e. the result must be reproducible; (3) it should be easy to instal and to remove; (4) it should be adapted for discontinuous use; (5) it should be usable at different flow rates; (6) it should have a relatively long lffespan and (7) it should be relatively inexpensive. On the basis of at least one of these criteria, the diatomic filter, the ceramic filter, the M E cartridges, the wound polypropylene fibre cartridges with end caps and the wound polypropylene fibre cartridges with double open ends failed the tests. With regard to nematode retention, promising results were obtained with the crossflow filtration technique; such a system, however, is very expensive. Almost total retention of the plant-parasitic nematodes present was achieved with a filtration system composed of M D E cartridges. A filter unit composed of polyester felt filter bags retained all the plant-parasitic nematodes.
CROP PROTECTION Vol. 11 F e b r u a r y 1992
100.0
0.0 32.0 85.0 0.0 79.2 99.2
The lifespan of such filter units is primarily determined by the concentration of solids in the drainwater. As this concentration differs among production plants, but also varies according to the season, the lifespan is difficult to predict. The I p,m filter bags, incorporated into the irrigation system of a commercial greenhouse, needed replacement only after 140 m 3 water had passed through. In hydroponic-type systems the irrigation water is supplied at a high flow rate. Filtration of this total volume of water would require a high-capacity filtration system. As plant-parasitic nematodes are present only in drainwater there is no need for such a system. As the returning drainwater is not under pressure, direct filtration is excluded. A system has therefore been developed in which the drainwater is caught in an initial reservoir from which it is pumped (10001h 1) into a second tank ( F i g u r e l ) , passing four filters (a 150~tm metal gauze cartridge and three polyester felt filter bags (80, 1 and 1 gin). Collection of the water in an initial reservoir offers two advantages. On the one hand the nematodes are able to sediment, resulting in a considerable reduction of the suspended nematodes. This technique is also used in drinking-water plants and results in a significant reduction of the nematode concentration (Murad and Bazer, 1970; Mott, Mulamoottil and Harrison, 1981). On the other hand it enables the filtration flow rate to be uncoupled from the flow rate of the drainwater; this makes it possible to use a small-capacity filtration system working at low differential pressure. Problems with insoluble pesticides are less frequent in this system. Filtration of the drainwater of hydroponic-type systems, combined with the use of micropropagated plants and the Drainwater
li
Filter unit
To the greenhouse
ii!ifi
Figure 1. System for filtering nematodes out of drainwater, independent of the flow rate of the returning water
Nematode control in drainwater by filtration: M. Moens and G. Hendrickx use o f a n e m a t o d e - f r e e s u b s t r a t e m a k e s t h e p r o d u c t i o n o f n e m a t o d e - f r e e o r n a m e n t a l p o t p l a n t s m o r e likely.
Acknowledgements T h e a u t h o r s a r e g r a t e f u l to R e n a a t M o e r m a n s o f t h e Biometric Unit of the Agricultural Research Centre Ghent f o r his a d v i c e a n d to M a g d a V a n d e p u t t e a n d L u c r 6 c e Matthys for their technical assistance.
73
Lamberti, F. (198l) Plant nematode problems in the Mediterranean region. Helminthol. Abstr. Ser. B, Plant Nematol. 50, 145-166 Moens, M. and Hendrickx, G. (1989) Sensitivity of Meloidogyne incognita second stage juveniles to UV-irradiation. Meded. Fac. Landb Wetensch. R~jksuniv. Gent 54, 1187 1193 Moens, M. and Hendriekx, G. (1990) Nematode infection by recirculating nutrient solutions in gullies. Meded. Fac. Landb Wetensch. R~/ksuniv. Gent 55, 739 744 Mott, J. B., Mulamoottil, G. and Harrison, A. D. (1981) A 13-month survey of the nematodes at three water treatment plants in Southern Ontario, Canada. Water Res. 15, 729 738 Murad, 3. L. and Bazer, G. T. (1970) Diplogasterid and rhabditid nematodes in a wastewater treatment plant and factors related to their dispersal. J. Water Pollution Control Fed. 42, 106-114
References Dunne, R. and Donovan, M. (1!)77) Aphid control on tomatoes in a hydroponic system. Acta Hort. 82, 137 139
Peterson, R. L., Engelbreeht, R. S. and Austin, J. H. (1965) Freeliving Nematode Removal by Rapid Sand Filters. Paper presented at the National Symposium on Sanitary Engineering Research Development and Design, 27-30 July 1965, The Pennsylvania State University, University Park, PA
Hague, N. G. M. (1972) Nematode diseases of ftower bulbs, glasshouse crops and ornamentals. In: Economic Nematology (Ed. by J. M. Webster) pp. 409-434, Academic Press, London, New York
Seth, A. K., George, M. G., Bewtra, J. K. and Sharma, V. P. (1968) Nematode removal by rapid sand filtration. J. Am. Water Works Ass. 60, 962-968
Hendrickx, G. J., Coolen, W.A. and Moens, M.G. (1986) Search for Radopholus-free Calathea makoyana. Meded. Fac. LandbWetensch. Rijksuniv. Gent 51, 1325-1329
Staunton, W. P. and Cormican, T. P. (1980) The effects of pathogens and fungicides on tomatoes in a hydroponic system. Acta Hort. 98, 293-315
Geraert, E. (1983) Morphology and morphometry of Mesodiplogaster pseudolheritieri n.sp. (Nematcda: Rhabditida). Nematologica 29, 284 297 Jamart, G., De Prest, G. and Kamoen, O. (l 988) Control of Pythium spp. on ornamental plants in a nutrient-film system. Meded. Fac. LandbWetensch. Rijksuniv. Gent 53, 625-634
Wei, 1. W. T., Engelbreeht, R. S. and Austin, J. H. (1969) Removal of nematodes by rapid sand filtration. J. Sanit. Engng Div. Am. Soc. Civil Eng. 95, Proc. Paper 6384, 1 16 Received 8 April 1991 Revised 29 June 1991 Accepted 3 July 1991
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