Pollen beetle migration has started one to two weeks early across much of England, with growers urged to keep a close eye on their oilseed rape crops.
Bayer CropScience’s migration map has shown more than half of the monitoring stations south of a line between Warrington in Cheshire and Beverley in Yorkshire have indicated that migration has started.
The latest advice from the agrichemical giant is to use its three online maps to monitor the situation and keep up to date with the threat.
The new migration map shows when conditions favour migration, indicating when growers need to get into crops and assess average numbers of beetles per plant against thresholds.
Pollen beetle migration typically continues for four to six weeks. Growers should continue to monitor the threat during this period using the maps or assess when crops are past the economically vulnerable stage.
This is normally when flowering has begun, with about three-quarters of the plants in a field at GS61 and 10% of flowers open.
Pollen beetles have become an increasing threat in recent years due to a growing number of cases of resistance to commonly used pyrethroid sprays.
|Revised control thresholds for winter and spring OSR|
|Fewer than 30 plants/sq m||Threshold is 25 pollen beetles/plant|
|30-50 plants/sq m||Threshold is 18 pollen beetles/plant|
|50-70 plants/sq m||Threshold is 11 pollen beetles/plant|
|More than 70 plants/sq m||Threshold is 7 pollen beetles/plant|