Striped Cucumber Beetles Damaging 40-80% of Pumpkin Fruit

Cucumber beetle feeding on green pumpkin

Although we once thought the 2001 insect season was over, it appears that many pumpkin/squash growers may not yet be ready to forget about their 6-legged friends. On Sept. 14th we strongly urged pumpkin growers to start watching for a potential increase in striped cucumber beetle and/or squash bug infestations, particularly on ripening fruit. During the past 2 weeks, this potential concern became a reality as very high numbers of cucumber beetles began aggregating on large pumpkins in the Rosemount area (East-central MN; Dakota Co.). At one location, damaged fruit increased from 5 to 40% in one field (see Figure 1), and up to 80% at a second research site. The type of "scaring damage" to the fruit is illustrated in the enclosed photographs. A summary of the increasing infestation and damage to fruit is also provided below.

Cucumber beetles feeding on ripe pumpkin

Why so many beetles now? The relatively dry summer months may have been conducive to larval survival (feeding on root tissue), contributing to a significant fall emergence of adults. Some of the recent activity and movement of beetles was likely due to very warm sunny days. As we postulated earlier, their movement to fruit also appears to be correlated with the dry-down of vine/leaf tissue, and/or tillage of vegetable tissue in preparation for harvest. As shown in Figure 1, fruit damage dramatically increased following the first hard frost and onset of vine death (Sept. 25th).

Striped cucumber beetle damage on pumpkin

Potential for control? As indicated previously (see Sept. 14th article), an insecticide application may be necessary in one or more fields, to control the beetle and minimize feeding damage. However, with vines crossing over multiple rows this time of year, it may be difficult to spray with ground equipment. Also, because of the aggregating behavior of the beetles, it may be possible to limit insecticide applications to areas with high infestations. Some fields are now being harvested for October sales. If you still have pumpkins/squash that will remain in the field for several weeks, check these fields carefully for damage. If you believe it is necessary to use an insecticide, remember to check the pre-harvest interval (PHI: minimum number of days between last spray and harvest). Table 1 below summarizes the PHI for several insecticides labeled for pumpkins/squash.

One alternative control strategy we are investigating (for small plantings, e.g. <3 ac), is a new trap design (Trece, Inc.) to lure beetles out of a field, and thus minimize damage to plants and fruit. As shown in Fig. 1, the preliminary data suggest a suppressive effect, where fruit damage is less in the field with traps. We need more data to further test this control option. These data clearly show that the traps work well as a monitoring device.

Table 1: PHI of insecticides used for control of cucumber beetle