Cucumber beetles seem to be able to sense a newly emerged cucurbit field as soon as it breaks through the ground. The beetles often emerge in flushes, making monitoring and control an ongoing job.
Imidacloprid (Admire, Grapple) can be applied as an at-planting treatment, either in the seed furrow or in the transplant water. It can also be applied immediately after planting as an over-the-row drench. These methods of application typically provide 4-6 weeks of cucumber beetle control.
Endosulfan is still registered for use in cucurbit crops until December 31, 2016. This long phase out period will hopefully allow us to pursue the registration of a suitable alternative. Endosulfan is most effective when applied during cooler temperatures. New flushes of beetles arriving in the field may require subsequent treatments.
For organic growers, kaolin clay (Surround) may be applied to the foliage as a beetle deterrent.
The threshold for control is 0.5 to 1 beetle per plant. Inspect at least 100 plants across the field to get a good idea of the overall population. Cucumbers are particularly susceptible to Bacterial Wilt disease which is transmitted by the cucumber beetle. As a result, cucumbers have a fairly low tolerance for this pest. Beetles are most active during the early morning hours and often hide during the heat of the day.