Efficacy of Pre-Planting Herbicides on Meloidogyne Incognita Infecting Okra Plant under Greenhouse Conditions

A pot experiment was carried out in order to evaluate the efficacy of four pre-planting herbicides i.e. Amex 48%, Atrazine, Nitrofen and Stomp 5% in comparison with Oxamyl on Meloidogyne incognita infecting okra plant cv Hyper Doki 1 under greenhouse conditions (25±5 oC). It was evident that all tested pesticides improved plant growth parameters and reduced nematode with various grades. Atrazien overwhelmed other treatments in improving plant growth parameters for plant length (19.84%), whole plant fresh weight (29.32%) and shoot dry weight (66.03%), respectively, followed by Nitrofen for the same plant criteria with values of 15.53, 21.67 and 59.86%, respectively. Moreover, Oxamyl as a nematicide showed extensive values in improving plant growth criteria and ranked first in suppressing nematode population density in soil, galls and eggmass numbers. Atrazine accomplished the reasonable reduction percentage in nematode population density in soil followed by that of Amex 48% application with value of 25.27%. There was no significant differences between the values of RGI and EI indices which achieved equal values with those of nematode alone(4).


INTRODUCTION
Herbicides are chemicals that used to control injurious weeds all over the world. The most common application of herbicides occurs in row-crop farming, where they are applied before or during planting to maximize crop production by minimizing other harmful flora. A few hebicides have been reported to have an effect on population of plantparasitic nematodes. herbicide mixture of acifluorfen and bentazon decreased populations of Heterodera glycines (Browdie et al., 1994). In some cases, nematode populations have increased following application of herbicides. The herbicide vernolate, metributzin and trihralin increased the number of soybean cyst nematode (H. glycines) egg production by 37 and 134 percent in soybean (Kraus, et al., 1982). The mixture of herbicide alachlor and nematicide fenamiphos caused a late season reappearance of H. glycines population (Sipes and Shmitt. 1989). Indifferent responses of nematodes to herbicides treatment have also been reported by Liphadzi et al., (2005). Few information are reported on the effect of the common herbicides on nematode in Egypt. The present investigation was conducted to determine the efficacy of some commonly used pre-planting herbicides i.e. Amex 48%, Atrazine, Nitrofen and Stomp 5% on root-knot nematodes, Meloidogyne incognita infecting okra plant Hyper Doki 1 under greenhouse conditions.

MATERIALS AND METHODS
A pot experiment was carried-out at the Nematology Research Unit (NRU)of the Agricultural Zoology Department, Fac. of Agric., Mansoura University in order to determine the effect of four pre-planting herbicides i.e. Amex 48%, Atrazine, Nitrofen and Stomp 5% in comparison with Oxamyl (Vydate 24 % E.C) at the recommended dose (0. 3 ml) on Meloidogyne incognita reproduction and the resulting effect on okra plant growth (Table 1). Twenty plastic pots (15cm-diam) containing 1600g.steam-sterilized clay sand soil (1:1, v:v) treated with four herbicides each and mixed with soil. After seven days, thirty five pots were sown with three seeds of okra each. Two weeks later, okra seedlings were thinned to one seedling / pot and inoculated with 1000 M. incognita second stage juvenile to thirty seedlings and left five seedlings (pots) without nematode and any treatments to serve as control.
Plastic pots were then arranged in randomized complete block design in the greenhouse and treated horticulturally and irrigated with water as needed. Plants were harvested after 45 days from nematode inoculation and plant growth criteria i.e. shoot and root lengths and fresh wight as well as shoot dry weights were determined and recorded. Infected roots of each plant /treatment were washed with tap water, fixed in 4% formalin for 24 h and examined for the number of galls and eggmasses per root system, and recorded. The root gall index (RGI) and egg mass index (EI) were estimated according to the scale given by Taylor and Sasser (1978) as follows: 0= no galling or egg-masses, 1= 1-2 galls or egg-masses, 2= 3-10 galls or egg-masses, 3= 11-30 galls or eggmasses, 4= 31-100 galls or egg-masses and 5= more than 100 galls or egg-masses. M. incognita (J2s) were separately extracted from 250 cc soil of each treatment by sieving and modified Baermann technique (Goodey, 1957), counted and recorded. This process was repeated three times and the average of J2 / 250 cc soil was determined and recorded.
Statistically, the obtained data were subjected to analysis of variance (ANOVA) (Gomez and Gomez, 1984) followed by Duncan's multiple ranges to compare means (Duncan, 1955).

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Stomp 5%  86 nematode population density in soil that averaged 26.93%, followed by that of Amex 48% application with value of 25.27%. The relative lowest reduction percentage of this nematode criterion was resulted by treatment of Nitrofen with value of 18.32 % as compared with nematode alone, (Table 3).
Regarding, galls and egg-mass numbers, a low reduction in number of galls and eggmasess on okra roots was recorded by all tested herbicides with values of 7.34 and 36.94% for Atrazine, respectively. In the meantime, it was evident that Amex 48%, showed the lowest gall and eggmass reduction percentages with values 2.96 and 26.71% for the same criteria, respectively.
Concerning root galling and eggmasses indices, there was no significant differences between the values of RGI and EI indices which achieved equal values with those of nematode alone (4).
Moreover, Oxamyl as a systemic nematicide ranked first in suppressing nematode population density in soil, galls and eggmass numbers on roots with values of 68.66, 90.91 and 100.0%, respectively, with low RGI and EI indices which averaged 1.3 and zero vs 4 for nematode alone.  Apparently, the importance of utilizing herbicides are essential for controlling harmful weeds within nontarget effect in soil micro-organisms such as phytonematodes in various agricultural crops. However, results of the present work proved this phenomenon in influencing M. incognita development associated with ameliorating plant growth parameters of infected okra cv. Hyper Doki 1 under the application of four pre-planting herbicides i.e. Amex 48%, Atrazine, Nitrofen and Stomp 5% in comparison with Oxamyl under greenhouse conditions. These findings are in accordance with that of Browdie et al., (1994) who reported that herbicide combination of acifluorfen and bentazon decreased populations of Heterodera glycines. Similar trend observed by Singh and Nandram (2004) who found that use of herbicides in rice and wheat had a significant harmful effect on nematode populations. On the other hand, The observed data were disagreed with Kraus et al., (1982) who found that herbicide vernolate, metributzin and trihralin increased the number of soybean cyst nematode (H. glycines) egg production by 37 and 134 percent in soybean. The response of different soil nematode groups to herbicide application may indicate a change in soil ecosystem processes. The change in nematode community structure may alter the soil decomposition pathway (Zhao et al. 2013). The toxic effect of tested herbicides may be due to chemical composition of their integrated materials. To improve the accepting of the effects of herbicides on the soil nematode population, additional large-scale, longterm and comparable research experiments with different agroecosystems are required to be done.