African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 4, Num. 4, 1996, pp. 471-475

Greenhouse assessment of maize growth and yield response to nematode control with aldicarb

H.F. RIEKERT

Grain Crops Institute, Private Bag X1251 Potchefstroom 2520, Republic of South Africa

(Received 10 August, 1996; accepted 30 October, 1996)

Code Number: CS96088
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ABSTRACT

Aldicarb provided effective nematode control on maize planted in pots of nematode infested soil in the greenhouse. An average grain yield increase of 50.7 g per plant was recorded. No significant growth response to aldicarb was observed for the following criteria: plant length, number of internodes, length of internodes 1 - 5 and circumference of the fourth internode. No yield increase or growth response was obtained in soil with low levels of nematode infestation.

Key Words: Aldicarb, growth response, maize, nematicidal effect, yield

RESUME

Nons avons montre que aldicarb peut etre utilise effectivement comme controle contre terre infeste par nematodes. L'experimence a ete finalisee en mais plante dans une serre. La moyenne de rendement de grain du mays a augmente a 50.7 g par plante. La reaction de croissance n'etait pas considerable. En ce qui concerne: la longeur des plantes, le nombre d' internodes longeur d 'internodes 1 - 5 et la circumference du quatrieme internode. Nous n'avons pas trouve une augmentation de rendement en terre avec peu d'infestation.

Mots Cles: Aldicarb, reaction de croissance, mais, effet de nematodes, rendement

INTRODUCTION

Crop growth enhancements associated with the use of nematicides have been observed by numerous investigators. Norton et al. (1978) stated that increased maize (Zea mays L.) yield with nematicide applications could be the result of nematode control, insect control or growth enhancement by the nematicides. The latter possibility has not received much attention in South Africa and is mainly covered in literature reviews (McDonald and De Waele, 1987). Scholte and s'Jacob (1983) obtained effective nematode control with oxamyl applied to maize. They observed growth enhancement in the early growth stages of plants but it had only a slight effect on yield.

Crop growth enhancement associated with the use of aldicarb has also been reported on many other crops but has not always been associated with yield increases (McEwen et al., 1979; Barker et al., 1988). Aldicarb generally increased the number of branches and flowers of pea plants (Pisum sativum L.), the number of cotton flowers (Gossypium hirsutum L.) (McEwen et al. 1979) and growth of soybean (Glycine max (L.) Merr.) (Barker et al. 1988). Aldicarb treatment in tobacco (Nicotiana tabacum L.) resulted in increased growth which resulted in increased harvestable foliage (Barker and Powell, 1988).

The nematode control - yield increase relationship may further be complicated by as yet unknown effects of nematicides on non-target soil microflora and -fauna, which may affect crop performance. Aldicarb enhanced growth of Rhizobium spp. associated with cowpea (Vigna sinensis L.) at 2 ppm but inhibited growth at 5 and 10 ppm in a laboratory test. Soil application of aldicarb to cowpea reduced the number of nodules but enhanced dry matter production of the plants (Sekar and Balasubramanian, 1979).

Environmental conditions may also play a role in growth regulating effects of aldicarb. This is due to the varying rate of degradation of aldicarb with variation in soil type, pH, temperature, moisture and organic matter (Barker et al. 1988).

The aim of this study was to determine whether yield increases observed in maize plots treated with aldicarb during recent field studies could be attributed to nematode control or plant growth enhancement by aldicarb.

MATERIALS AND METHODS

The maize hybrid PAN6528 was planted in pots in a greenhouse using two soils. The main difference between the soils were the different natural nematode infestation levels. Soil A was collected from a field near Viljoenskroon with a high natural nematode infestation (more than 500 + 200 plant parasitic nematodes in 200 ml soil). The important plant-parasitic nematodes present were Pratylenchus zeae, P. brachyurus (9:1 ratio), Meloidogyne javanica and M. incognita (9:1 ratio). The clay content was 4.8% and pH 5.09. Soil B, sold as common gardening soil, had a low natural nematode infestation (less than 10 plant parasitic nematodes in 200 ml soil) with a species composition similar to soil A, a clay content of 10.9% and a pH of 4.61. Soil B was included as an upper control as no yield increase was expected due to low nematode infestation levels unless aldicarb resulted in growth or yield enhancement. Since only data between different treatments within either soil A or B were compared, the difference in clay content did not affect results and interpretation.

Half of both soils was steam pasteurised for eight hours at 120 C. Eighty asbestos pots (35 x 35 x 36 cm) were each filled with 40 l of soil, 40 pots for each soil type. One seed was planted per pot. Based on soil nutrient analyses fertilities of both soils were supplemented by addition of 2.63 g N; 2.775 g P; 3.405 g K; 3.445 g Ca and 2.36 g Mg per pot. A top dressing of 5.60 g N per pot was applied to both soils six weeks after plant emergence. Pots were watered weekly till flowering by means of calibrated drip irrigation, and increased to twice a week at the commencement of ear formation to prevent wilting of plants.

The trial consisted of four treatments for each soil type. These were pasteurised soil; pasteurised soil + aldicarb; unpasteurised soil, and unpasteurised soil + aldicarb. Ten pots were used per treatment. Treatments with pasteurised soil (estimated total nematode control) were included as a second upper control as no yield reactions were expected  unless caused by aldicarb. Aldicarb, 150 g kg^-1 a.i. granular, manufactured by Rhone-Poulenc, was applied at a rate of 0.33 g product (is 0.05 g a.i.) per pot, equivalent to the field recommendation for maize of 1 g product (is 0.15 g a.i.) per linear metre row length.

Total plant length (from stem base to the tip of the last extended leaf) was measured seven times during the growing season, namely 55, 62, 69, 76, 84, 92 and 139 days after planting. At harvest the number of internodes, length (cm) of internodes 1 to 5, circumference (cm) of the fourth internode and yield (g) per plant were determined. Nematodes within the roots were extracted at harvest by means of the sugar centrifugal flotation method (De Waele et al., 1987) and the adapted NaOCl method for root-knot nematode extraction (Riekert, 1995). The trial layout was a randomised complete block. Nematode numbers were log(x + 1) transformed, and data were subjected to analyses of variance.

RESULTS AND DISCUSSION

Aldicarb application to soil B did not result in significant differences in either plant growth, yield or nematode numbers (data not presented). This can be attributed to low natural nematode infestation and lack of growth enhancement by aldicarb. Soil B therefore sufficed as an upper control to evaluate possible growth enhancement by aldicarb.

No significant differences in plant length were recorded in soil A (Table 1). Similarly, no significant differences in number of internodes, length of internodes 1 - 5 or the circumferences of internode 4 were recorded (Table 2). Aldicarb treatment, therefore, did not result in significant growth enhancement in this greenhouse study.

TABLE 1. Average plant length (cm) of maize in soil A*

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Time      Pasteurised   Pasteurised soil  Unpasteurised   Unpasteurised
(days)       soil          +aldicarb          soil       soil + aldicarb
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 55         124.5           112.5             96.4            120.0 
 62         152.7           151.5            143.2            153.7
 69         202.0           198.2            197.8            204.5
 76         218.9           217.2            224.0            225.9
 84         273.5           266.9            274.3            278.7
 92         305.6           296.5            327.3            295.3
139         311.4           298.5            328.5            298.9

* No significant differences between means were observed at P < 0.05 (LSD).
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TABLE 2. Average circumference (cm). length of internode 1-5 (cm) and number of internodes for soil A*

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Internode data      Pasteurised  Pasteurlsed   Unpasteurised  Unpasteurised
                         soil   soil+aldicarb      soil       soil+aldicarb
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Circumference            7.58       7.75           7.39          7.61 
Length internode 1-5    69.5        67.5          69.6          77.2 
Total no. of internode  17.4        17.3          16.8          17.0

* No significant differences between means were observed at P < 0.05 (LSD).
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Yield differed significantly (P = 0.038) between treatments in soil A (Table 3). The yield response in soil A can be attributed to reduction of nematode numbers due to aldicarb treatment. The difference of 50.72 g in yield (Table 3) between unpasteurised soil and the same soil treated with aldicarb is ascribed to the effect of nematodes on yield (Table 3).

TABLE 3. Nematode numbers log(x+ 1) transformed (P=0.0071) and average yield in g/plant (P=0.0379) for soil A

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Treatments                   Nematode numbers                     Yield 
             ------------------------------------------------- (g plant^-1)
             Pratylenchus  Meloidogyne  Meloidogyne  Meloidogyne
                               eggs       larvae        total
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Pasteurlsed soil    0.794 e*  0.428 a    0.497 a       0.815 b    219,26 a 
Pasteurised soil 
      + aldicarb    0.277 a   0.139 a    0.069 a       0.179 a    237.06 ab

Unpasteurised soil  8.419 c   2.396 b    2.691 b       3.417 c    221.25 a
Unpasteurised soil 
     + aldicarb     6.608 b   0.069 a    0.179 a       0.248 ab.  271.97 b