The effects of soil sterilants on the cereal cyst-nematode (Heterodera avenae Woll.), take-all (Ophiobolus graminis Sacc.) and yields of spring wheat and barley

In a 3-year field experiment on sandy loam at Woburn, methyl bromide, chloropicrin, D-D mixture, dazomet, formalin and mercury salts were applied in the first year only, or in the first and second years, before drilling spring wheat. In the third year, their residual effects on spring barley were measured. All sterilants except mercury decreased cereal cyst-nematode ( Heterodera avenae ) numbers and take-all ( Ophiobolus graminis ) incidence, and increased crop yields in the year they were applied. Dazomet gave the best control of H. avenae in the first year and controlled O. graminis best in both years of application. In the third year, O. graminis increased in all plots previously treated (except after two successive D-D treatments), but H. avenae increased only after formalin. Two formalin applications more than trebled the H. avenae egg count by the end of the third year and depressed the yield of barley. Two successive applications of chloropicrin gave the best nematode control.
Other fungus diseases, Fusarium foot rot, Pythium root rot, eye-spot ( Cercosporella herpotrichoides Fron.) and sharp eye spot ( Rhizoctonia solani Kühn), were uncommon and sterilants had no detectable effects on them. The largest aggregate straw yield (3-year total) was obtained from two applications of dazomet, but the best yields after treatment in the first year only were given by D-D and methyl bromide.