Pumpkin Insect Management
Rick Weinzierl, Extension Entomologist
Department of Crop Sciences, University of Illinois
In 2003, as in most years, a few key pests have been predominant in pumpkin production. Cucumber beetles, squash vine borers, squash bugs, and corn rootworm beetles have lived up to their roles as perennial pests, and aphids, perhaps including the soybean aphid, have been important as late summer vectors of virus diseases.
Striped and spotted cucumber beetles overwinter as adults and move to cucurbits in the spring and early summer. Two generations develop each year in most of Illinois. Spring infestations of spotted and striped cucumber beetle populations were down somewhat in much of the state in 2003 following a winter that was colder than most in recent years. For processing pumpkins that are somewhat susceptible to bacterial wilt (caused by a pathogen transmitted by cucumber beetles), the recommended threshold for early season control of cucumber beetles is 1 beetle per plant (or less). Because jack-o-lantern pumpkins are not very susceptible to bacterial wilt, controlling cucumber beetles early in the season is warranted only if counts exceed 5 per plant or defoliation is severe. Late in the season, especially on jack-o-lanterns, controlling striped or spotted cucumber beetles may be necessary if they begin to feed on the ripening fruits. Feeding on fruits provides an infection pathway for pathogens and makes the fruit less attractive for marketing. Insecticides that control cucumber beetles include planting-time applications of Admire or Furadan and foliar applications of carbaryl (as Adios or Sevin), Pounce, Asana, or Capture. Organic growers may use rotenone or Surround. To minimize bee kills if control is necessary when plants are in bloom, growers should make applications when bees are not foraging (early morning or late evening) and use formulations that are least toxic (Adios or Sevin XLR-Plus).
The squash vine borer is the larval stage of a moth in the family Sesiidae – the clearwinged moths. The body and wings of adult moths are colored with red and black scales, and they resemble wasps. Unlike most moths, they are active in the daytime, and also unlike most moths, large portions of their wings lack scales, hence the name “clearwinged moths.” Moths lay eggs at the base of vines, and larvae tunnel within the vines, causing them to wilt. This insect overwinters in the pupal stage, and moths emerge from late May (south) to July (north). In the southern part of Illinois, two generations develop in many years. Control guidelines for squash vine borer call for scouting as soon as vines begin to run, looking for the moths and for entrance holes at the base of vines (from larval tunneling). Treat when first damage is noted and again about a week later. Several insecticides are effective for vine borer control, including Capture, Sevin, Asana, Pounce, and Ambush. As with cucumber beetles, organic growers may see some control from applications of rotenone or Surround. At the small scale, mounding soil around the base of vines can encourage adventitious root growth from portions of the vine beyond the point of vine borer damage.
Squash vine borer adult (left) and larva (right)
T The insect most often identified as the scourge of squash and pumpkin production is the squash bug. Squash bugs are “true bugs” – insects in the order Hemiptera, characterized in part by mouthparts in the form of a sucking beak that arises from the tip of the head. They overwinter as adults and move into squash and pumpkin plantings in June (south) and July (north). Adults lay reddish-brown to bronze eggs in small groups on leaves, and those eggs hatch in 7 to 10 days. Immature stages are called nymphs, and growth through 5 nymphal stages takes 5 to 6 weeks in much of the Midwest. In southern parts of the Illinois and farther southward, adults mature soon enough to mate and lay eggs to start a second generation in the same summer, but in most of the upper Midwest, there is only one generation per year.
The key to controlling squash bugs is to detect their presence early and take action immediately. Growers are advised to scout for egg masses (clusters), use a threshold of 1 egg mass per plant, and apply insecticides for squash bug control as soon as nymphs hatch and begin feeding. The registered insecticide that is most effective for squash bug control is Capture. Other insecticides that provide some control include Asana and Pounce, but if growers rely on these insecticides it is imperative that they make applications when nymphs are small ... most insecticides are not at all effective against large nymphs or adults. Sabadilla was once available for organic growers to use for squash bug control, but it is no longer formulated for sale in the U.S. Natural pyrethrins will give some control, but as noted above, application when nymphs are very small is key to any success. Natural pyrethrins do not persist on foliage for more than several hours after application.
Squash bug eggs (above left), nymphs (above right) and adult (left)
Late in the season, adults of the western corn rootworm, a major pest of field corn, become numerous in cucurbits. Western corn rootworm beetles resemble the striped cucumber beetle, but the underside of the abdomen (the belly) of the western corn rootworm beetle is yellowish (not black as it is in the striped cucumber beetle). In addition, the stripes that mark the forewings (that form the “shell” that covers the back part of the beetle) of the western corn rootworm beetle do not reach all the way to the end of the forewings and the margins of the stripes are blurry, not distinct as they are in the striped cucumber beetle. Controlling western corn rootworm beetles on pumpkins may be necessary if beetles are feeding on pumpkin fruits. Because western corn rootworm populations adapted to crop rotation have developed in east-central Illinois, population densities have risen dramatically in recent years, and their control in late summer has been necessary in many pumpkin fields in this portion of the state. The foliar insecticides listed earlier for cucumber beetle control (carbaryl [as Adios or Sevin], Pounce, Asana, Capture, and rotenone) also are effective against western corn rootworms.
Western (left) and northern (right) corn rootworm beetles. The western corn rootworm beetle is more often a pest of pumpkins in late summer.
Aphids, particularly the cotton-melon aphid, sometimes colonize pumpkins in Illinois. When colonies are building on plants, usually in the late summer, their control with an insecticide may be warranted. Capture or Pounce may provide some control, but Actara, Fulfill, or Metasystox-R (all developed as “aphicides”) may be more effective.
A winged aphid on a leaf surface
Aphid-borne virus diseases of pumpkins have become common in several areas in late summer in 2003, and growers may be tempted to use insecticides to try prevent such outbreaks. Unfortunately, the major viruses of cucurbits are transmitted in a nonpersistent manner by aphids that “pass through” vegetable plantings, make a feeding probe or two, and then moving on. Using insecticides to kill aphids within plantings does not prevent introduction of viruses into fields and rarely if ever does much good in the control of viruses transmitted in a nonpersistent manner.