At this time of year, high numbers of cucumber beetles can quickly wreak havoc in pumpkin and squash fields. Adult beetles feed on the rind, rendering the fruit unmarketable (Figure 1).
Scout fields regularly, at least once a week. During the heat of the day beetles often hide in weedy spots, in blossoms or in soil cracks at the base of the fruit. Scouting in the early morning or evening often gives a better estimate of beetle populations. In addition to looking for the beetles, also inspect the fruit for signs of feeding damage.
The existing thresholds are based on spring feeding activity and the risk of bacterial wilt transmission. For fall feeding, spray if populations appear to be increasing or if there are signs of damage to the fruit.
Matador Insecticide (cyhalothrin-lambda) recently received registration for the control of cucumber beetles on cucurbit crops. Endosulfan (Thionex 50WP/Thiodan 4EC) is also registered. If there are still bee hives present in the field area, remove them before spraying.
For organic growers, kaolin clay (Surround WP) discourages beetles from becoming established in the crop. However, it does leave a fine white powdery clay residue on the fruit. While the residue is usually easily removed during washing, do not apply Surround close to harvest to avoid unsightly powder on the fruit during marketing.
For more information on the biology of the cucumber beetle, visit Ontario CropIPM at: http://bit.ly/PeZ8zT