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.