Growers are advised to re-think their cereal agronomy strategies and use of seed treatments, to ensure the best possible establishment and vigour of crops this autumn, as a result of the neonicotinoid bans.
The greatest challenge from the loss of Deter (clothianidin) will be control of the vectors of barley yellow dwarf virus (BYDV), including bird cherry aphid and rose grain aphid, warns Wynnstay Group crop protection manager Dr Simon Pope.
He says autumn infection of winter wheat and barley can often result in yield losses of up to 50 per cent, meanwhile in winter, barley losses of 75 per cent have been recorded.
Dr Pope says to reduce the risk of BYDV transmission, careful consideration should be given to destroying the so-called ‘green bridge’.
“Volunteer cereals already carrying the virus can act as a source of inoculum; aphids feed on infected plants then migrate to newly emerged cereal crops and transfer the virus,” he says.
Stubble management is important, and it is not sufficient to rely on cultivation alone, since aphids can survive underground on plant remains and move to the new crop as it germinates and emerges, he adds.
And it is important to destroy the volunteer cereals with glyphosate before cultivation to ensure the aphid vectors are not buried with a food/inoculum source.
Delaying drilling can be a useful strategy for many growers, particularly where aphids can be a problem. Although aphid vectors will still be on the wing and will migrate into crops and infect the plants they feed on, the rate of spread of virus within the crop will be reduced.
The rate of secondary spread of aphids within a crop is greater at higher temperatures. By delaying drilling the crop is emerging into cooler conditions, so pressure should be lower.
Dr Pope says, “The number of day degrees can be measured to assess the risk of secondary spread and numbers and species of aphid caught in suction traps are published, also aphid numbers in crops can be monitored.
“Taking all of this information into account enables a risk assessment and pyrethroid insecticides should be applied as necessary from the 1–2-leaf stage of the crop and possibly earlier in high risk situations.”
Repeat applications could be required if aphid numbers are high and temperatures remain mild, he advises, warning that there is increasing resistance to pyrethroids being reported in grain aphids.
Dr Simon Pope BASIS FACTS BETA