Withsome warmer days the Pollen Beetles are on the move, at a time coinciding withmany oilseed rape crops growing through stem elongation and starting to bud -the time when they are most susceptible to feeding damage. Pollen Beetles havebeen reported active in Dorset and Bedfordshire recently.
Theincreased risk of pyrethroid resistance among Pollen Beetle populations, whichis now believed to be widespread across most of the UK, indicates growers andagronomists should be looking at Plenum to control all beetles.
Growersare being urged to inspect crops regularly for signs of beetle migration and totreat when thresholds are reached. New advice from the HGCA advocates controlat lower thresholds in thick crops, which could be especially relevant thisseason after strong autumn growth, warned Syngenta Oilseed Rape Manager, GaryJobling.
Cropswith a high plant population have less ability to branch out and compensate forthe Pollen Beetle damage to buds, compared to less dense crops, he explained.They are typically the first crops to come into bud, and will therefore beunder the most intense feeding pressure as the beetles search for pollen.
MrJobling stated that, in the past, advice had been to make an initialapplication of the leading pyrethroid, Hallmark Zeon, as soon as thresholds arereached. Crops would then continue to be monitored for signs of continuedbeetle activity that could indicate resistance, when a second treatment using Plenumwould be applied.
However,such is the widespread nature of resistance, the recommendation now is to usePlenum as the first choice where there has previously been any concern overresistance in the region, he said.
Giventhe intense pressure to get on with fieldwork for other crops as soon as groundconditions permit, he believed many growers will find it difficult to undertakerepeated monitoring of oilseed rape, or find the time for a second applicationif the pyrethroid performance is poor.
MrJobling reiterated that Plenum can be used up until the end of the yellow budstage of the crop, which would provide the crop with full protection fromPollen Beetle damage. Once plants start to flower, the beetles are attractedto open flowers where the pollen is readily accessible. At that stage theybecome positive pollinators for the crop, with little or no further significantdamage to remaining buds.
Plenumshould be used at the rate of 0.15kg/ha for Pollen Beetle control in the spring,compared to the rate of 0.3 kg/ha used for aphids in the autumn to preventspread of Turnip Yellows Virus (TuYV). Growers are permitted to make twoapplications per crop, one at each of the two different rates and timings. Theaddition of a high-quality 90% methylated rapeseed oil in the tank mix had beenreported to enhance the efficacy of all applications.