South: Explosion in pollen beetle numbers

Last month I complained about the wet conditions. Since then we have had the driest March I can remember. Can we now have some rain please?

Crops are currently quite stressed, nitrogen uptake is being limited by the dry conditions and this has steadied up the growth of most crops. Oilseed rape crops on light gravely land needs rain soon if potential yield is not going to be compromised.  

Wheat crops are currently recieving their T0 fungicide applications based round a chlorthalonil/triazole mix. As far as growth regulation is concerned, I am using half rate chlormequat at the moment and not using any Moddus (trinexapac-ethyl). The risk of phytotoxic effects with PGR mixes in the current dry conditions is quite high.

IIf needed, and if it ever rains, a more robust growth regulator mix will be used at T1.

Winter rape crops are now well into stem extension. Pollen Beetle numbers have exploded in the unseasonably warm conditions. The conventional threshold for winter rape is 15 beetles/plant, but an attack this early, in some cases before the flower buds are visible warrants a lower threshold since damage will occur for a longer period of time. 

Given the increasing resistance of the pest to pyrethroid insecticides, in some parts of the country, control could be difficult. If problems controling pollen beetle have been experienced in the past, other insecticides with different modes of action like Biscaya (thiacloprid), Rumo (indoxacarb) and Plenum (pymetrozine) should be used.

These typically cost 3-5 times as much money, but it is worth remembering that the most expensive input you use is the one that didn’t work!! 


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