Vegetable Insect Update – May 25, 2018

David Owens, Extension Entomologist, owensd@udel.edu

Striped cucumber beetles have been roaring into watermelon fields now that the sky has cleared. Our threshold for watermelon, which is not susceptible to a bacterial wilt, is 2 per plant. A lot of folks are going out with or planning to go out with a foliar neonic. Be careful with the product you use. Some only permit soil applications (imidacloprid – Admire Pro and other labeled formulations) while other active ingredients can be applied by soil or foliar depending on the specific trade name you use. The difference is in the formulation and how the product interacts with leaf tissue (ex: thiamethoxam – Platinum is for soil, Actara is for foliar application). Also check your application restrictions. Some products can only be used at the full rate once in the field while others can be applied several times in-season.

Another question that comes up is residual control. Efficacy trials are hard to get good data on with this pest in a field setting due to the unreliable nature of cucumber beetle pressure. Some data suggests that products should be effective for up to 5 or more weeks, other data and personal anecdotes say no more than about 2 weeks. I would be very interested to hear your input. Please also note that Vydate, effective on nematodes, does not have cucumber beetle on the label. While it does affect cucumber beetles, it is not consistent.

The question has come up regarding application timing and bee safety. A foliar application is going to be a bit more toxic because of the additional exposure route. If you are within 2 weeks of flowering, either a chemigation treatment or switching products to acetamiprid (ex. Assail) would be a little more bee-friendly. A great table indicating insecticide toxicity to bees can be found here: http://msue.anr.msu.edu/uploads/resources/pdfs/Minimizing_Pesticide_Risk_to_Bees_in_Fruit_Crops_(E3245).pdf. Other products that you can use with less risk to bees BEFORE flowering include Sevin and various pyrethroids. Pyrethroids and Sevin are very toxic to bees, but the residues are short lived, and effective for no more than about a week under ‘good’ conditions. Apply no later than several days before hives are placed. Unfortunately, that limited activity may not give us adequate cucumber beetle protection, necessitating follow up applications in shorter intervals – increasing risks to bees.

Live mating cucumber beetles and a dead individual on a leaf.

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