Concord grape hard bumps on leaves and stems
What is this and how is it treated? I've been removing the leaves and bumpy stems. Should I spray with Sevin? Powdery mildew is not present.
Kent County Michigan
Hard to tell without a picture but I think you might had what are called tumid galls.
There is a small insect that lays its eggs in the new grape leaves and shoots. The larvae form a gall to live in. This is not usually a major problem in grapes. It comes and goes and controling it with an insecticide is difficult because the spray needs to when the eggs are being laid. Sevin will not control it once the galls have formed
Here is a link to more information
Thank you Mark. Does removing the affected leaves make any difference? What's the best product to use when it's the egg laying stage? When is the egg laying stage? Or will this grape pest naturally move on?
What about a dormant oil that's used on fruit trees? I've only read about this and not sure how it's applied and when
So you agree it is tumid gall?
Not much to be done. Dormant oil would not help.
I think there are several generations (2 or 3) a year and egg laying for the first generation is just before bloom. It is not really a big problem for most grapes, but some wild grapes and some hybrid varieties do seem to attract them.
Here is a link to more information. Commercial growers use a new systemic insecticide called Movento but it is very expensive and you would need to buy a lot more than you need.