Short communication
Biological control of plant-parasitic nematodes in pigeonpea ®eld
crops using neem-based products and manurial treatments
Mohammad Akhtar
Department of Plant Protection, Institute of Agriculture, Aligarh Muslim University, Aligarh 202 002, India
Received 10 September 1998; received in revised form 8 February 1999; accepted 10 February 1999
Abstract
The paper presents an account of a ®eld plot experiment to investigate the in¯uence of soil applications of neem-based (Achook and Suneem G) and crop fertilizer (urea and cattle manure) treatments, separately and in combination on free-living, and plant-pathogenic nematode populations and crop productivity. All the treatments signi®cantly decreased the number of plant-parasitic nematodes with increasing doses. Combinations of both neem-products with urea were most effective in reducing plant-parasitic nematode populations. The neem products and product combinations with urea signi®cantly decreased numbers of free-living nematodes compared to controls; however, numbers increased in the cattle-manure-treated plots. The growth of pigeonpea (Cajanus cajanL.) was improved in all the treatments, in part due to the control of plant-parasitic nematodes and in part due to manurial effects. Urea was phytotoxic at 330 kg N/ha applied alone; however, it was not phytotoxic at this rate in combination with the neem-based products.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Azadirachta indica; Biological control;Cajanus cajan; Cattle manure; Free-living nematodes; Plant-parasitic nematodes
1. Introduction
Widespread concern about the consequences of conventional pesticide use has resulted in increased interest in alternative pest control measures. Natural products derived from neem (Azadirachts indica A. Juss.) including leaf, kernel and seed powders, seed extracts and oil have been reported to control several agricultural pests including plant-parasitic nematodes (Schmutterrer, 1990; Akhtar and Mahmood, 1994, 1996; Akhtar, 1998). In the past few decades the ef®cacy of deoiled neem cake, neem oil and neem leaf as soil amendments for the control of phytopatho-genic nematodes has been studied by Akhtar and Alam, 1993a, b and Akhtar and Mahmood, 1997. Reduction in population densities of plant-parasitic
nematodes in response to application of organic man-ure amendments has also been reported in many studies, e.g., Muller and Gooch (1982), but practical use depends on a large and readily available supply of these materials. Free-living nematodes may accelerate the decomposition of soil organic matter (Abrams and Mitchell, 1980). Numbers of free-living, microbivor-ous nematodes increase rapidly in the soil following the addition of organic and inorganic fertilizers (Mar-shall, 1977), while there can be a corresponding decrease in plant-parasitic nematodes (Mankau and Minteer, 1962; Tomerlin and Smart, 1969).
The present ®eld study seeks to assess the combined effects of two neem-based products and manurial treatment in the form of urea and cattle manure on densities of plant-parasitic and
living nematodes and the growth of pigeonpe a crop in ®eld soil.
2. Materials and methods
The experimental ®eld was at the Aligarh Muslim University, Agricultural Research Farm at Qila Road, Aligarh, India. The site on an alluvial soil of pH 8.3 with 1.0% organic matter was thoroughly ploughed to a depth of 10±15 cm and divided into small plots measuring 2 m3 m separated by 0.5 m wide alleys. Treatments comprised urea, or cattle manure applied at 110, 220, or 330 kg N/ha; `Achook' (azadirachtin; Godrej Agrovet, India) and `Suneem G' (Azadirachtin Sunida Exports, India) applied at 5, 10 and 15 kg/ha and combinations of each urea treatment (110, 220, 330 kg N/ha) with each neem product treatment (5, 10, 15 kg/ha, respectively). Untreated plots received neither neem application or fertilizer. Cattle manure was applied to plots 4 weeks before planting and other treatments were applied at the planting of pigeonpea (Cajanus cajan L.). The experimental design was a randomized complete block with ®ve replications of each treatment including untreated plots. Crop culti-vations, the control of insect, foliar disease and weed problems and the use of ®eld irrigation were uniformly applied across the experiment according to local practice.
Soil samples for nematode assay were collected from each plot before sowing (May 1994) and one day after harvest (July 1994). A bulked soil sample of 30± 40 cores was taken from the rhizosphere of each plot using a 2.5 cm diam cylindrical corer. Cores were pooled and a 100 g sub-sample was taken for nema-tode extraction by Cobb's sieving and decanting method followed by Baermann funnel extraction (Southey, 1986). Plant-parasitic and free-living nema-todes were identi®ed and preserved in 5% formalin. Total numbers of free-living species were assessed, while individuals of the plant-parasitic species, Hoplolaimus indicus Sher, Helicotylenchus indicus Siddiqui,Rotylenchulus reniformis Linford and Oli-veira,Tylenchus ®liformis Bastian and Meloidogyne incognita (Kofoid and White) Chitwood were sepa-rately counted.
Sixty days after sowing, the pigeonpea plants from all the plots were harvested and the dry weights of
shoots and roots were recorded. Dry weights were determined after oven drying for 12 h at 608C.
3. Results
3.1. Effect of populations of plant-parasitic nematodes
Populations of plant-parasitic nematodes differed greatly according to treatment. Populations increased in untreated plots because pigeonpea is a highly-susceptible crop. The addition of both neem-products, manure and urea signi®cantly reduced the total num-ber of plant-parasitic nematodes (Table 1). The great-est reduction in plant-parasitic nematode populations was observed with combinations of neem products and urea applications followed by neem products alone, urea and manure in descending order. Increasing the rates of all the applications signi®cantly reduced the populations of plant-parasitic nematodes.
3.2. Effect on populations of free-living nematodes
In unamended soil, populations of free-living nematodes were not signi®cantly different between the time of sowing and harvesting the crop. In all the treated plots except those treated with cattle manure populations of free-living nematodes were signi®-cantly decreased (AVOVA, p< 0.05) compared with the control. However, neem treatments alone showed greater population decline at higher applications rates. Both urea and urea with neem showed a trend of increasing nematode abundance at higher applica-tion rates.
3.3. Effect on plant growth
Dry shoot and root weights of pigeonpea were increased in response to applications of both neem products, with or without urea, and cattle manure as compared with the untreated control (Table 1). Neem treatments at the highest rate increased shoot yields by a factor of three, compared with untreated control plants. Addition of urea further increased growth in plots treated with neem extracts. The ef®cacy of the two neem products was similar, and plant growth increased with increased doses of these materials.
Effect of manure and neem products on nematode populations and growth of pigeonpeaC. cajan
Soil amendments Rate Nematode populations/100 g soil, SE Whole plot harvest (g dry wt. per plant)
Plant-parasitica Free-living, SE Shoot Root Total SE
Hop Hel Rot Tyl Mel Total, SE
Pre-treatment 540 390 600 350 895 277534.0 209224.9 ± ± ±
`Achook' 5 kg/ha 90 65 110 60 100 42524.5 121248.4 14.8 10.5 25.32.18
10 kg/ha 70 55 90 45 55 31531.3 91829.5 17.5 11.3 28.82.07
15 kg/ha 52 41 78 32 35 23817.9 74217.7 20.5 12.4 32.41.97
`Suneem G' 5 kg/ha 89 60 120 65 99 44128.5 124119.5 15.2 10.5 25.73.07
10 kg/ha 72 57 91 46 55 32134.9 84242.3 17.5 11.5 29.02.17
15 kg/ha 54 44 78 33 36 24522.7 69228.4 20.2 12.5 32.53.99
Urea 110 kg N/ha 110 99 135 96 255 69542.9 87824.5 12.4 10.0 22.42.07
220 kg N/ha 95 90 105 64 221 57518.7 113531.5 13.5 11.5 25.01.05
330 kg N/ha 85 70 90 54 93 39224.3 140526.5 b b b
`Achook'urea 5 kg110 kg N/ha 69 54 89 44 62 31831.7 92018.4 17.1 11.5 29.22.17 10 kg220 kg N/ha 50 40 65 20 50 22522.9 120522.5 19.5 14.3 33.83.07 15 kg330 kg N/ha 35 28 44 16 43 16617.9 139529.9 21.5 15.0 37.42.18 `Suneem G'urea 5 kg110 kg N/ha 70 55 89 44 53 33114.5 102018.4 17.5 11.4 28.92.18 10 kg220 kg N/ha 45 34 51 26 56 21218.7 130022.5 19.5 13.5 33.02.05 15 kg330 kg N/ha 30 25 35 20 41 15109.5 154033.9 20.0 15.7 35.72.17 Cattle manure 110 kg N/ha 136 140 185 165 214 84031.5 244031.5 13.5 12.0 25.51.97
220kg N/ha 99 98 160 105 133 59522.7 279039.4 14.8 12.4 27.22.05
330 kg N/ha 78 78 107 95 122 48017.5 317539.4 16.3 13.1 29.41.87
Untreated (control) 1550 1450 1055 1439 15056 2055078.5 445044.5 7.3 5.0 12.30.85
Data are mean of five replicates.
aHop ±Hoplolaimus indus, Hel ±Helicotylenchus indicus, Rot ±Rotylenchulus reniformis, Tyl ±Tylenchus filiformis, MelMeloidogyne incognitajuveniles. bPlants died before the measurements were taken.
M.
Akhtar
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Applied
Soil
Ecology
12
(1999)
191±195
Urea treatments were as effective as cattle manure at the 110 and 220 kg N/ha rates although urea was phytotoxic at 330 kg N/ha when added alone. How-ever, urea was not phytotoxic at this rate in combina-tion with the neem-based products. In the untreated plots plant growth parameters were much reduced, presumbly due to a lack of fertilizer and an increase in the population of plant-parasitic nematodes.
4. Discussion
All manures and neem treatments signi®cantly decreased populations of plant-parasitic nematodes and increased plant growth compared to untreated control plots. These results con®rm earlier ®ndings (Akhtar and Alam, 1993b) that a combination of a neem-based product, `Nimin' with fertilizer could increase crop yield and reduce numbers of plant-parasitic nematodes. `Nimin' contains azadirachtin ± a neem triterpene that acts by delaying the rapid transformation of ammonium nitrogen into nitrate nitrogen (nitri®cation inhibition). This ensures slow release and continuously available nitrogen during plant growth in addition to a nematicidal effect. In contrast, in the current study the largest dose of urea (330 kg N/ha) was markedly phytotoxic, whereas at 110 or 220 kg N/ha urea was effective in suppression of nematode populations and enhanced plant growth performance. The two in combination (urea plus neem products) promote even greater growth. Rodriguez-Kabana (1986) pointed out that nitrogen fertilizers releasing ammonium N in the soil are most effective in suppressing nematode populations and stated that the rate required to obtain signi®cant suppression of nematode populations is generally in excess of 150 kg N/ha. Thus, combination of neem-based pro-ducts with urea may have reduced plant-parasitic nematode populations and provided nitrogen during plant growth.
One of the most interesting ®ndings was that neem alone decreased free-living nematode populations and this effect showed a dose response i.e., fewer nema-todes at higher application rates. Although urea treat-ments also reduced numbers of free-living nematodes compared with the untreated plots, the dose response was quite different i.e., larger numbers at higher application rates. Most importantly when neem and
urea treatments were combined, free-living nematode numbers were also relatively higher at higher applica-tion rates of both neem and fertilizer. The important implication of this is that urea use in combination with neem would seem to ameliorate the deleterious effect of the latter on potentially bene®cial nematodes species.
The availability of N was different in the treatments even when the amount added was equal, particularly in the case of manure treatment, because different sub-strates have different mineralization rates, so that application of equal amounts of N in organic form will not necessarily lead to equal amounts of inorganic N being made available to the crop. Other nutrients and nematicidal compounds were present in different quantities in the different treatments, which may have affected the nematode populations. The decomposition products of manure, neem products and urea may also be directly toxic to plant-parasitic nematodes. Application of these materials may be suitable manipulated to provide an economical alternative for the control of plant-parasitic nematodes which is less disturbing to agroecosystems than conventional nematicides. Further research on the combination of crop husbandry practice and use of natural products is needed.
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