The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

Published source details McGrath P.F. & Bale J.S. (1990) The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England. Annals of Applied Biology, 117, 31-43.
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This study is summarised as evidence for the following.

	Action	Category
	Alter the timing of insecticide use Action Link

Alter the timing of insecticide use

A randomised, replicated study in 1984-1985 in North Yorkshire, UK (McGrath & Bale 1990) found that barley yellow dwarf virus Luteovirus spp. created more patches of stunted barley Hordeum vulgare in plots sprayed on 13 November (averaging 11-16 patches/plot) than on 23 October (6-16 patches) or 31 October (7-14 patches). The area of stunted patches (ranging 1,124-4,087 cm²) only differed between spraying dates in barley sown on 6 September rather than 18 or 27 September, and showed an increase with delayed spraying date. Effects of spray timing on English grain aphid Sitobion avenae (a carrier of the virus) depended on insecticide type. On all spraying dates, deltamethrin reduced aphids with no reinfestation later in the season. Demeton-S-methyl reduced aphids but limited reinfestation occurred (affecting < 3% of plants) in plots sprayed earliest (23 October). Pirimicarb also allowed reinfestation (affecting up to 6% of plants), particularly when applied early (23 October) or to plots sown on 6 September. The authors suggest that spraying early was effective for persistent insecticides, but spraying later (after aphid migration) was more effective for other insecticides. Yield (ranging 6.6-7.1 t/ha) was not consistently different between spraying dates. Three spraying dates were tested in plots of 2 x 24 m, replicated twelve times across three blocks testing sowing date effects.