Development and evaluation of in-crop monitoring as a method of identifying BYDV high risk situations

Abstract

Annual, regional and between field differences in the numbers of aphids which infest cereals during the autumn provide opportunities for targeting insecticide treatments at the crops which have the highest risk of developing damaging Barley Yellow Dwarf Virus (BYDV) infection. In many autumns, only the small minority of crops which follow undesiccated ploughed-in grass leys have a high risk of developing damaging BYDV infection.

Using aphid and BYDV infection data collected from 20-45 crops annually in six growing seasons of winter barley in the west of Scotland and Northern Ireland, and aerial aphid density data of the Rothamsted Insect Survey, methods of identifying the autumns when the risk of damaging BYDV infection is likely to be high have been devised. These methods may be used to issue pre-drilling information on the risk of BYDV infection each autumn, and they can be used to organise more extensive and frequent aphid sampling of cereals in autumns which are predicted to be at high risk.

The aphid and BYDV data have also been used to identify field/farm characteristics which are associated with large aphid populations and subsequently higher levels of BYDV infection. These field/farm characteristics may be used to target insecticide applications at crops which have the highest numbers of aphids, ensuring that aphid populations are controlled in crops that require treatment while reducing the unnecessary use of insecticides in crops which have low numbers of aphids.

This new scheme, Strategic Monitoring, has the potential to reduce the annual cost of insurance spraying to control aphids during the autumn which has been estimated at £10 million. By reducing the uncertainty of when (which autumns?) and where (which regions and which fields?) damaging BYDV infection may develop, the need for insurance spraying of all crops is lessened. More years' aphid and BYDV data from winter barley crops are required to further test and refine Strategic Monitoring. To improve the ability of field/farm characteristics to identify high risk fields, a national database of field/farm characteristics and aphid/BYDV incidence needs to be constructed using data collected over a number of years. This study has greatly increased knowledge of BYDV in autumn-sown cereals but six years is not long enough to encounter sufficient variation in aphid/BYDV incidence to confidently forecast the disease risk on the regional and field scale required by advisers and cereal growers.