Appropriate aphicide doses for summer aphid control on wheat

Summary

Sector:
Cereals & Oilseeds
Project code:
PR229
Date:
01 April 1998 - 31 March 1999
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£129,956 From HGCA (Project No. 1714)
Project leader:
J N Oakley ADAS Rosemaund, Preston Wynne, Hereford HR1 3PG

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About this project

Abstract

Aim. The project aimed to demonstrate the potential of reduced aphicide rates for control of summer aphids in wheat in a range of commercial crops over two seasons.

Conclusions. Sites were established on two commercial wheat crops at or close to each of ADAS Boxworth, Bridgets, High Mowthorpe, Rosemaund and Terrington in both 1998 and 1999. At each site early and later sown crops were used. Each experiment consisted of spray applications with recommended label rate and one-third dose applications of pirimicarb or alpha-cypermethrin and a full rate application of dimethoate at GS 61 compared to an untreated control. More aphids successfully overwintered on crops in the mild winter weather of 1997/98 than have been recorded since 1988/89. Overwintered infestations carried aphid parasitoids and fungal diseases. Wet weather during June further favoured the development of high levels of parasitism and fungal disease. In consequence aphid infestations were controlled naturally before reaching damaging levels at all ten sites. In 1999 grain aphid numbers were reduced by thunderstorms in late May and early June and did not recover to exceed threshold numbers at either GS 61 or 73 at any of the sites. The rose-grain aphid predominated at Terrington and Rosemaund, reaching near damaging levels in one crop at Rosemaund. In the earlier sown crop at Bridgets, a significant yield response was obtained to all the aphicide treatments. This yield increase was obtained despite numbers of aphids remaining below the accepted threshold level of 5 aphids per tiller (equivalent to two thirds of tillers infested with aphids). The crop appeared to be particularly susceptible to aphid damage, due to the combined impact of low soluble stem carbohydrate reserves and a severe attack from wheat blossom midge

Implications for levy payers. A one third rate application of pirimicarb was as effective as the full label rate in controlling moderate aphid infestations. These results confirm earlier findings that a reduced rate can be used as part of an integrated aphid control strategy to tip the balance in favour of the aphids predators. The reduced rate application of alpha-cypermethrin was less effective than the recommended rate. At neither rate was the control of rose-grain aphid infestations on the underside of the leaves as effective as that given by dimethoate or pirimicarb. The results have provided valuable information on the conditions under which natural enemies and wet weather can combine to control aphid infestations. The degree of incidental control of wheat blossom midge was also measured. Dimethoate, pirimicarb and alpha-cypermethrin reduced the proportion of damaged grains by 33, 13 and 28% on average. But at some sites pirimicarb and alpha-cypermethrin increased damage by up to 20%, presumably by killing useful predators when not timed correctly to control the midge.

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