Insect pests of OSR – The Pollen Beetle
As the name suggests this beetle loves to eat pollen and so is intimately associated with pollen-rich species of flowers such as Oil Seed Rape (OSR.)
Once there are enough flowers then there is sufficient pollen for them to live happily on.
Unhappily for OSR growers there is always a rush when the “smell of food” lures them to the kitchen door. Since the door is not open then they break in and steal what there is on the table even though its not quite ready.
This breaking of doors and theft leads to a reduction in the number of viable flowers and later pods. Since some of the main yield bearing pods are formed early on in the development of the plant and on the main raceme the damage caused is significant.
So, should I spray these chaps?
WOSR: Forward crops of WOSR are now green bud and occasional pollen beetles have been sighted. This pest needs sustained periods of 10 – 15 degrees to break hibernation and migration can last for 4 – 6 weeks. The green/yellow bud stage is the most susceptible to pollen beetle attack but migration of the pest and the susceptible growth stage do not always coincide. By assessing plant populations you can get an indication of the pollen beetle threshold for an individual crop, seen in the table below:
Should the threshold be met for treatment it should be borne in mind that pollen beetle resistance to pyrethroids is now widespread in the UK so the use of these insecticides should be minimized in this arena. According to the Insecticide Resistance Action Group there are currently three modes of action approved for use against pollen beetle: pyrethroids (e.g. lambda cyhalothrin), oxadiazines (indoxacarb) and neonicotinoids (e.g. acetamiprid). RUMO (indoxacarb) @ 300g / ha or INSYST (acetamiprid) @ 200g/ha.