Archive Article: 1997/10/04
The reply to
wheat bulb fly
I WOULD like to make some observations on your article in the last issue (Crops w/e Sept 20).
In deciding to live with wheat bulb fly by sowing early, at higher seed rates, Nigel Carey and his agronomist John Purslow should be aware that this approach is equally favourable to the pest, as it is to the crop.
By providing surplus food to feed the larvae, they are likely to enhance greatly the proportion surviving to adulthood next July, and progressively build up a bigger problem in the area.
Provided that they continue to sow early and increase seed rates, growers may get away with this approach for some time. But if adverse weather delays sowing at some point in the future, these growers could find that they have created too high a population to control with current available insecticides.
They could also prove to be unpopular with any neighbours who are not willing, or able, to sow early at high seed rates.
My preference for cultural control is to manipulate cultivations, to draw the pest away from fields destined for wheat. Cultivation of fields going to oilseed rape in early August to attract the egg-laying flies is my favoured policy.
On the predatory beetle front, I can offer some encouragement from previous studies. When re-sampling fields for wheat bulb fly, we often find eggs which have been eaten by ground beetles.
The predation is rarely sufficient to control a high population, but in one field near Alford we once found that the numbers eaten equalled the economic threshold numbers of 2.5m/ha.
On checking the cultivations used, we indeed found that the field had only had a light, non-inverting cultivation, compared to other fields nearby, where the eggs had been buried and predation was minimal.
Jon Oakley,
ADAS Bridgets, Martyr Worthy, Hants.