A raspberry fly is a dangerous raspberry pest that can deprive you of the main part of the crop, and if you do not take any measures, then the whole crop. What are the methods of struggle with raspberry stem fly? What you need to know about her? Raspberry fly stem winters in the upper soil layers under raspberry bushes. Her flight coincides with the time of regrowth of young shoots. In the Kuban, this is approximately in the middle of April, and in central Russia - in the middle of May.
Knowing the time of departure of the fly, you can process the young tips of the shoots, for example, with the preparation Iskra or Actellic. But the chemical method is recommended to use only if the raspberry stem fly is damaged more than 50% of the landings. Still, chemistry is chemistry - it will destroy the pests, but we will also get. .. A good way to get rid of the larvae that have settled for the winter, is digging the soil around the raspberry bushes in the fall.
In the photo below, the raspberry shoot may be damaged by a stem fly - until it is clear that the shoot has stopped growing - the point of growth does not develop - the introduction of the fly into the shoot has occurred. The pest has not yet damaged the shoot - wilt, blackening of the leaves - ahead. If you did not have time to scare away the crimson stem fly in time, then the only way out is pruning damaged shoots. 
The larva of a fly, if not trimmed in time, can reach the base of the shoot. In this case, the escape can not be saved - it dries. As soon as the raspberry begins to bloom, the pest, having reached the base, moves from the shoot into the soil, pupates there and repeats the process: the fly - the eggs - the larvae.
If we allow the development of this process from the beginning to the end, then there is nothing left for the gardener than to cut the damaged shoots to the ground.
But you can and should do it differently. There is a second way to deal with a stem fly.
As soon as you notice that the green tip of the shoot has begun to wilt, and the tips of the leaves turn black, cut about half of the branch. The cut parts of the branches must be burned immediately - the larvae are left there - you cannot let them survive - therefore you cannot be late with pruning.
By the way, you will surely notice that the stem fly lays eggs in the tops of the most powerful shoots. These are the shoots do not need to cut to the ground - because they produce the main crop. In addition, strong side replacement shoots begin to grow around them from the ground.
Cut only half of the damaged shoots to half if you are not late. To the base, to the roots, cut only weak shoots.
By cutting out all damaged shoots as close to the ground as possible( the first method), you will deprive yourself of the main part of the crop, and if you allow the stem fly to reproduce, then the entire crop. But the second method, on the contrary, preserves and even increases the yield of berries due to incomplete pruning.
