With good migration conditions forecast for this weekend and first flowers opening in many crops, growers are advised to check the ‘new migration’ map daily and monitor crops as soon as indicated.
A cool week with much of the country struggling to reach 10C did not suit pollen beetle migration. Consequently today’s Bayer Pollen Beetle Predictor ‘percent migration’ map has hardly changed from last Friday’s bulletin showing that most of England still has 60 to 85 percent of this season’s migration still to come. A handful of home counties met stations are showing migration half complete, but this is the exception. In Scotland and the borders migration has hardly started and there is 90% still to come.
A marked change in the weather is on the way for this weekend though and with temperatures forecast to climb to the mid to high teens Centigrade significant migration into crops is expected. Many crops now have first flowers opening (GS60) but will remain susceptible to pollen beetle damage until they are flowering in earnest i.e. when more than 20% of buds on main shoots are flowering on more than three quarters of the crop (GS62). Even with the good conditions forecast it could be another week before they reach this stage.
In the meantime, where numbers exceed threshold, crop growth stage will be a key consideration in treatment decision-making. Product labels restrict use of Plenum (pymetrozine) and Rumo (indoxacarb) to before first flowers open (GS60) but use of Biscaya (thiacloprid) is unrestricted by growth stage.