With some warmer days the Pollen Beetles are on the move, at a time coinciding with many oilseed rape crops growing through stem elongation and starting to bud - the time when they are most susceptible to feeding damage. Pollen Beetles have been reported active in Dorset and Bedfordshire this week.
The increased risk of pyrethroid resistance among Pollen Beetle populations, which is now believed to be widespread across most of the UK, indicates growers and agronomists should be looking at Plenum to control all beetles.
Growers are being urged to inspect crops regularly for signs of beetle migration and to treat when thresholds are reached. New advice from the HGCA advocates control at lower thresholds in thick crops, which could be especially relevant this season after strong autumn growth, warned Syngenta Oilseed Rape Manager, Gary Jobling.
“Crops with a high plant population have less ability to branch out and compensate for the 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 be under the most intense feeding pressure as the beetles search for pollen.”
Mr Jobling stated that, in the past, advice had been to make an initial application of the leading pyrethroid, Hallmark Zeon, as soon as thresholds are reached. Crops would then continue to be monitored for signs of continued beetle activity that could indicate resistance, when a second treatment using Plenum would be applied.
“However, such is the widespread nature of resistance, the recommendation now is to use Plenum as the first choice where there has previously been any concern over resistance in the region,” he said.
Given the intense pressure to get on with fieldwork for other crops as soon as ground conditions permit, he believed many growers will find it difficult to undertake repeated monitoring of oilseed rape, or find the time for a second application if the pyrethroid performance is poor.
Mr Jobling reiterated that Plenum can be used up until the end of the yellow bud stage of the crop, which would provide the crop with full protection from Pollen Beetle damage. “Once plants start to flower, the beetles are attracted to open flowers where the pollen is readily accessible. At that stage they become positive pollinators for the crop, with little or no further significant damage to remaining buds.”
Plenum should 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 prevent spread of Turnip Yellows Virus (TuYV). Growers are permitted to make two applications per crop, one at each of the two different rates and timings. The addition of a high-quality 90% methylated rapeseed oil in the tank mix had been reported to enhance the efficacy of all applications.
