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Vol. 4. No.4, pp. 477-481 1996 Economic feasibility of nematode control in dryland maize in South Africa
H.F. RIEKERT
ARC-Grain Crops institute, Private Bag X 1251, Potchefstroom 2520, Republic of South Africa
(Received 10 August, 1996; accepted 30 October, 1996)
Code Number: CS96089
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Text: 18.6K
Graphics: Line drawings (gif) - 3.2K
ABSTRACT Eighteen nematicide trials were conducted over a period of four seasons in the western maize production area of South Africa. The effect of nematode infestation on maize yields in aldicarb and carbofuran treated plots compared with untreated controls was investigated. The study indicated that increased yield associated with nematicide application was not necessarily financially warranted. The present cost of nematicides registered for maize is the most important constraint in the economic control of nematodes under local conditions. Key Words: Aldicarb, dryland maize, economic feasibility, nematodes RESUME Dix huit essais ont ete menes pendant une periode de quatre saisons Sur un champ de Production du mais en Afrique du Sud. L'effet d 'infestation de nematodes des rendements du mais plante en serre traite avec aldicarb & carbofuran a ete analyse et compare avec des controles. Le resultat a indique qu'une augmentation avec l'application de nematicides etait necessariement et financierement exigee. Le cout actuel du nematocide requis pour le mais est la contrainte la plus importante dans le controle economique des nematodes suite aux conditions locales. Mots Cles: Aldicarb, mais en terre seche, faisabilite economique, de nematicides INTRODUCTION Maize (Zea mays L.) is traditionally produced under a monoculture dryland system in South Africa (De Waele and Jordaan, 1988). The local status of Plant-parasitic nematodes and their chemical control on maize has received considerable attention (Walters, 1979a, b; Zondagh and van Rensburg, 1983; Mc Donald and De Waele, 1987; Mc Donald et al, 1987). Keetch and Buckley (1984) listed 36 plant-parasitic nematode species on maize in Southern Africa, which differ in economical importance. Nematicides have been used increasingly by local maize producers as a result of the above-mentioned reports (Mc Donald and De Waele, 1987 and Mc Donald et al., 1987). The latter authors, however, reported inconsistencies in nematode control on dryland maize.
The aim of a nematode control strategy is to protect plants from nematode infestation and reduce loss of income to the producer (Rivoal and Cook, 1993). The economic feasibility of nematicide treatments is of considerable importance in local maize production, since the dryland cultivation has an inherent risk. In order to allow for economic maize production, the financial benefit must exceed the cost of nematicide application.
The aim of this study was to determine whether granular nematicide application, as commonly used by commercial maize producers, is economically feasible. On-farm trials were conducted under dryland conditions. The insecticidal properties of the nematicides were not considered in this study. MATERIALS AND METHODS Field trials were conducted on seven fields in the western region of the maize production area from 1991 to 1994. Mean annual rainfall in the study area is in the order of 450 mm, and occurs at irregular intervals during the growing season. Fields were located in the Leeudoringstad, Ottosdal, Viljoenskroon, Potchefstroom, Bloekomspruit, Lichtenburg and Delareyville districts. Treatments were aldicarb, 150 g kg^-1 a.i. granular (1 g m^-1 row^-1 product, is 0.15 g a.i.) and carbofuran, 100 g kg^-1 a,i. granular (1.5 g m^-1 row^-1 product, is 0.15 g a.i.), and untreated control plots. Each plot was a 50 m row and was replicated 10 times for each treatment. Since on-farm trials were conducted, the cultivars used were dependent on producers' choice (Table 1 ). Maize was planted by means of a mechanical planter, equipped with a calibrated nematicide applicator. Soil preparation, fertilisation and any other cultivation activities were carried out according to the system preferred by the particular producer.
Row spacing was 1.5 m, except at Ottosdal and Delareyville where a 2.4 m row spacing is prescribed by the yield potential of the area. An intra-row plant spacing of 0.3 m was used at all localities. The average plant population varied from approximately 16 000 plants ha^-1 to 22 000 plants ha^-1. Planting date was determined according to local rainfall. Trials were planted between 15 October and 15 November of each season. To prevent a differential effect of aldicarb and carbofuran on other pests, such as stem borers and aphids, a contact insecticide was applied as needed, including the untreated control. Trials were harvested at a grain moisture content of 13% with a mechanical harvester. Each row was harvested separately and yield was converted to tons ha^-1.
Calculation of the economy of nematicide application was based on the cost of nematicides only, since the cost of application during planting could be regarded as negligible. All other production costs were excluded for the purpose of this study due to the considerable differences between production regions. The net income (gross income minus cost of nematicide) of the two treatments were compared to the net income of the untreated plots. Income exceeding that of the control implied a net benefit whereas an income lower than the control implied a net loss. No comparison of data was made between localities or seasons. The economics of each trial was considered separately.
Root and soil samples for nematode assessments were taken during flowering in all trials. Nematodes were extracted from roots using both sugar centrifugal flotation (De Waele et al., 1987) and the adapted NaOCl-methods for root-knot nematode extraction (Riekert, 1995). Soil sample extractions were done according to the method of Jenkins (1964). Nematode extractions were done to confirm the presence of plant parasitic nematodes in all treatments at the trial sites. Specific nematode numbers in treated plots were not important for the purpose of this study since the level of control obtained could be influenced by various factors beyond control of the producer. TABLE 1. Economic viability of aldicarb and carbofuran applications to dry land cultivated maize. Yield, gross income and the cost of the nematicide and financial benefit (+) or loss (-) for each application are shown
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Locality/Season Cultivar Treatment Yield Gross Nematicide Benefit
(kg ha^-1) income cost or loss
(Rand (Rand ha^-1)*
ha^-1)*
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Leeudoringstad
91/92 PAN 6479 Aldicarb 2189 974.1 129.1 + 87.6
Control 1702 757.4 0.0
92/93 PAN 6479 Aldicarb 2237 932.8 151.8 80.5
Carbofuran 2317 966.2 92.0 + 12.7
Control 2066 861.5 0.0
93/94 PAN 6479 Aldicarb 2655 876.2 151.8 + 89.4
Carbofuran 2693 888.7 131.7 + 122.1
Control 1924 634.9 0.0
Ottosdal
92/93 PAN 473 Aldicarb 1826 761.4 101.2 77.4
Carbofuran 1989 829.4 61.3 + 30.4
Control 1769 737.7 0.0
93/94 PAN 473 Aldicarb 3279 1082.2 101.2 85.4
Carbofuran 3440 1135.2 87.8 18.8
Control 3231 1066.2 0.0
Viljoenskroon
91/92 PAN 6528 Aldicarb 3099 1379.1 129.1 - 199.0
Control 3256 1448.9 0.0
92/93 PAN 6528 Aldicarb 6117 2550.8 151.8 - 155.2
Carbofuran 5504 2295.2 92.0 - 348.0
Control 6118 2251.2 0.0
93/94 PAN 6528 Aldicarb 5973 1971.1 151.8 165.0
Carbofuran 6013 1984.3 131.7 - 131.7
Control 6013 1984.3 0.0
93/94 PAN 6479 Aldicarb 5780 1907.4 151.8 99.0
Carbofuran 5540 1828.2 131.7 - 158.1
Control 5620 1854.6 0.0
93/94 PAN 473 Aldicarb 6027 1988.9 151.8 - 132.0
Carbofuran 6087 2008.7 131.7 92.1
Control 5967 1969.1 0.0
94/95 PAN 6528 Aldicarb 3820 1528.0 132.0 65.2
Carbofuran 3873 1549.2 131.7 43.7
Control 3653 1461.2 0.0
94/95 PAN 6479 Aldicarb 3753 1501.2 132.0 - 140.0
Carbofuran 3520 1408.0 131.7 - 232.9
Control 3773 1509.2 0.0
94/95 PAN 473 Aldicarb 3486 1394.4 132.0 - 228.0
Carbofuran 3867 1546.8 131.7 - 75.3
Control 3726 1490.4 0.0
Potchefstroom
92/93 PAN 6528 Aldicarb 1771 738.5 151.8 - 174.7
Carbofuran 1683 701.8 92.0 - 151.6
Control 1826 761.4
93/94 PAN 6528 Aldicarb 6836 2255.9 151.8 - 224.1
Carbofuran 6959 2296.5 131.7 - 163.4
Control 7055 2328.2 0.0
Bloekomspruit
93/94 PAN 6528 Aldicarb 3955 1305.2 151.8 - 343.0
Carbofuran 5213 1720.3 131.7 + 92.1
Control 4535 1496.6 0.0
Lichtenburg
93/94 PAN 6528 Aldicarb 3593 1185.7 101.2 + 64.8
Carbofuran 3504 1156.3 87.8 + 48.8
Control 3090 1019.7 0.0
Delareyville
93/94 PAN 6528 Aldicarb 3405 1123.7 101.2 - 48.1
Carbofuran 3061 1010.1 87.8 - 148.2
Control 3244 1070.5 0.0
* Currency: 1 US $ = 4.3 Rand
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RESULTS AND DISCUSSION Nematode species recorded were Pratylenchus spp., Meloidogyne spp., Paratrichodorus spp. as well as species from the Criconematidae, Hoploliaminiae and the Longidoridae. Species that dominated in numbers were Pratylenchus zeae, P. brachyurus, Meloidogyne javanica and M. incognita. The latter two species can be regarded to have the greatest damage potential, since their presence in high numbers often results in significant yield losses.
Inconsistent yield reactions, as previously reported in various South African studies, occurred in all trials during this study. Yield increased by up to 500 kg ha^-1 in nematicide treated maize in some trials (Table 1 ) but in most cases increases ranged from 50 to 350 kg ha^-1. These small yield increases did not cover the net cost of the nematicides and were thus considered uneconomical.
The lack of economic benefit on dryland maize is illustrated in Table 1. In 18 trials, only three aldicarb and five carbofuran treatments resulted in a net economic benefit to the producer. Only one carbofuran application resulted in an increased income exceeding R 100.00 ha^-1 (US $ 23) while four trials showed a benefit of less than R 50.00 ha^-1 (US $ 12). In twenty-four of the nematicide treatments a net loss was observed, ranging from R18.81 (US $ 4) to R 348.01 (US $ 81) ha^-1. This implies that some treatments resulted in yields insufficient to cover the actual cost of treatments, or that treatments sometimes resulted in yield redemptions, possibly due to water stress as a result of irregular rainfall.
Walters (1979b) reported yield increases ranging from 27.5 to 41.6% with carbofuran at a dosage rate of 2 kg a.i. ha^-1 in the same production region. Yield increases due to soil fumigation varied from 14.3 to 60%. However, no mention was made with regard to the economic implications of these treatments. Waiters (1979 b) also mentioned that a combination of climatic factors and genetic susceptibility of cultivars could greatly influence the effect of nematodes on maize. Walters' studies were conducted during a wet cycle lasting several seasons while these trials were conducted during intermittent drought lasting up to seven years in some of the regions. Thus rainfall varied considerably during the present trials resulting in wet as well as dry, unfavourable seasons. As growth of maize, nematode activity, reproduction and population species composition are influenced by climatic changes, this could be a possible explanation for differences in yield reaction between his and the present study.
The low producer price of maize in South Africa, together with the low yield potential of maize in these production areas (1-3 tons ha^-1) and high cost of nematicides, suggest that it is often uneconomical to use nematicides on maize in this region. The mediocre yield increases obtained after nematicide application in this study further supports the argument that nematicide applications on dryland maize with low yield potentials is not economical. The. yield increase needed for economic use of nematicides at an average yield potential of 2.5 tons ha^-1 and a nematicide cost of R132.00 ha^-1 is illustrated in Fig. 1. A higher maize price would reduce the yield increase required at the same yield potential and nematicide cost. Crop rotation systems could, however, influence this relationship, and nematode population build-up should be monitored. Crop rotation in this region often leads to a root-knot nematode build-up and high infestation levels are found to result in progressive, but significant yield losses of maize over seasons.
Although nematode control under dryland conditions is often not economically feasible, producers should not under-estimate the impact of plant-parasitic nematodes on maize. Population build-up of economically important nematodes must be prevented. Further studies on alternative control measures, particularly resistance breeding, are important. Plant - nematode interactions in crops such as maize are poorly understood and need intensive study to provide information for effective control measures to be developed. ACKNOWLEDGEMENTS Mr M.J. Schoeman, Ms G.A. Venter and A.S. van der Walt provided technical assistance. REFERENCES De Waele, E., De Waele, D. and Wilken, R. 1987. Effect of root mass on the efficacy of methods for extracting root-lesion nematodes from maize root samples. Phytophylactica 19:473474. De Waele, D. and Jordaan, E.M. 1988. Plantparasitic nematodes on field crops in South Africa. 1. Maize. Revuede Nematologie 11:6575. Jenkins, W.R. 1964. A rapid centrifugal flotation method for separating nematodes from soil. Plant Disease Reporter 48:692.
Keetch, D.P. and Buckley, N.H. 1984. A checklist of the Plant-parasitic nematodes of southern Africa. Technical Communication, Department of Agricultural Development, R.S.A. No. 195.213pp. McDonald, A.H. and De Waele, D. 1987. Effect of two nematicides on nematode populations associated with maize. Phytophylactica 19:475-478.
McDonald, A.H., Lui's, J.H., Loots, G.L. and De Waele, D. 1987. Chemical control of root lesion nematodes (Pratylenchus spp.) on maize in South Africa. Phytophylactica 19:479-483.
Riekert. H.F. 1995. A modified NaOCI technique for the extraction of root-knot nematode eggs and larvae from maize root samples. African Plant Protection I :41-43.
Rivoal, R. and Cook,R. 1993. Nematode pests of cereals. In: Plant Parasitic Nematodes in Temperate Agriculture. Evans, K., Trudgill, D.L. and Webster, J.M. (Eds.). CAB International. 648pp.
Walters, M.C. 1979a. The possible status of parasitic nematodes as limiting factors in maize production in South Africa. Proceedings of the Second Maize Breeding Symposium, 1976. Technical Communication, Department of Agricultural Development, R.S.A. No 142:112-118.
Walters, M.C. 1979 b. Present status of knowledge of nematode damage and control in South Africa. Proceedings of the Third South African Maize Breeding Symposium, 1978. Technical Communication, Department of Agricultural Development, R.S.A. No 152:62-66. Zondagh, S.G. and van Rensburg, J.B.J. 1983. Progress in nematode research in maize. Proceedings of the Fifth Maize Breeding Symposium, 1982. Technical Communication Department of Agricultural Development, R.S .A. No 182:64-66. Copyright 1996 The African Crop Science Society
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