Some effects of differently‐acting nematicides on the cereal cyst‐nematode (Heterodera avenae) and on the appearance of ‘scorch’ in spring wheat on light loamy sand

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Abstract
SUMMARY: In a field trial on light loamy sand, aldicarb was more effective than formalin or dazomet in controlling cereal cyst‐nematode on spring wheat.In the second year of the trial severe ‘scorch’ symptoms appeared and yield losses were greatest in aldicarb treated plots that received most nitrogen even though invasion of plants by juveniles of Heterodera avenae was greatly reduced. Before a dry spell in early summer, crop growth was best in those plots which had received most nitrogen but which finally yielded least; crop growth‐stage and the timing of dry periods are critical in the development of ‘scorch’ symptoms (early shrivelling, browning, and failure of ear emergence) on a light soil given a high rate of nitrogen. ‘Scorch’ occurred at the very luwest H. avenae population levels; the effects of fungal pathogens and NO3 nitrogen content of the crop remain uncertain. The rôle of copper in the ‘scorch’ condition could not be assessed since it was applied in a wetter year, in which ‘scorch’ failed to appear.