Some effects of 2,4-dichlorophenoxyacetic acid herbicides on nematode-infested cereals

SUMMARY After spraying an aqueous solution of 2,4-dichlorophenoxyacetic acid, 2,4-D (140 mg/100 ml/sq. yd) onto nematode susceptible (cv. Sun II) and resistant (cv. Manod) oats infested with Ditylenchus dipsaci the final number of nematodes per plant after eight weeks in both resistant and susceptible cultivars was greater in the sprayed than in the unsprayed plants. Seedlings (18 days old) sprayed two weeks after nematode inoculation tended to contain the largest number of nematodes. Spraying of Shell D50, a commercial 2,4-D herbicide (10 ml of concentrate /250ml/4 sq. yd) on nematode-infested oats resulted in a larger number of nematodes per plant than in the unsprayed plants but the difference was insignificant. The 2,4-D spray, which decreased the resistance of oats, but not of barley, to nematodes, caused plant cell hypertrophy and proliferation, which is a necessary response for favourable nematode development.