Herbicide effects in nematode diseases.

Herbicide use has provided agriculture with cost effective weed control and cont inued good crop yields, bu t occasional complications and adverse effects have been observed in the field. A recent review (1) discussed the effect of herbicides on plant diseases. Other studies have repor ted on the effects of herbicides on nematode infected crop plants (2,5,6,7,8,9,10,12). Effects ranged from aggravation of crop damage caused by nematode parasitism to reduced damage and lower nematode popula t ion levels. T h e differences appear to refiect the different systems, herb ic ide-crop-p lan t nematode, examined. This repor t extends these observations to include the effects of several herbicides applied by two methods to soybeans (Glycine max L.) and tomato (Lycopersicon esculentum L.) in root-knot nematode (Meloidogyne incognita) infested soil. Stock cultures of M. incognita were maintained on tomato (Lycopersicon esculentum cv. VF 145) in the greenhouse. In one experiment, soybean seeds, cv. Williams, were sown in 10-cm pots containing a mixture of sterilized clay soil and sand (1:1). After germination the seedlings were th inned to one plant per pot. Twentyday-old seedlings were each inoculated with 1,000 freshly hatched M. incognita larvae by pouring the nematode suspension into holes around the base of the plant, pressing the holes closed, and watering. Seven days after inoculation the herbicides EPTC (Sethyl dipropylthiocarbamate), glyphosate (N-[phosphonomethyl] glycine), or oryzalin (3,5-dinitro-N 4, N4-dipropylsulfanilamide) were applied at six concentrations as foliar sprays to runoff. Soil contaminat ion by the herbicides was prevented by a luminum foil covers. Plants were harvested 45 d later; the number of galls and nodules counted; and the shoot weight, shoot height, and pod and leaf number determined.