We still haven’t observed any Melonworm in the state this year, but we are on the
lookout and will be posting on our Facebook , Twitter , and Blog when they finally show up. To avoid the levels of damage to handles and rinds that
we saw last year we need to be considering insecticide applications as soon as the
moths show up.
In addition to the recommendations below, please consult the Southeastern Vegetable IPM Handbook for more guidance. If you have any questions about symptomology on your pumpkins,
contact your county agent to get samples sent to Sherrie Smith at the Plant Health Clinic for identification.
Insect Management We’ve seen less cucumber beetles this year compared to the last and it seems it has
something to do with the early heat. Squash bugs don’t seem to mind the heat as much
and have been around in summer squash all year and now are getting into pumpkins.
These two pests are generally considered the most serious pumpkin insect pests in
Arkansas as they transmit bacterial diseases. These diseases are well known by most
of our growers and typically lead to many unnecessary over-sprays, however, both pests
are very easy to scout for and these diseases can be prevented if insecticides are
on-time. Outside of our disease-causing pests, melonworm is the most serious pest
and widespread damage was observed across the entire state and MidSouth in 2021. We
don’t see those levels of damage every year and we need to be on the lookout for moths
and larvae to prevent major losses.
Cucumber Beetle Management Spotted and striped cucumber beetles are known to be an issue in Arkansas and can
transmit bacteria that can cause bacterial wilt (Fig. 1 and 2) . Adults feed on the foliage, flowers, and on the surface of the fruit, and plants
are susceptible to wilt transmission as soon as they emerge or are transplanted. Younger
plants (before 4-leaf) are most susceptible to the disease, therefore scouting twice
a week is necessary early on. Thresholds depend on the type of cucurbit you are trying
to protect and the age of the planting. An insecticide application should be made
to pumpkins when 1 cucumber beetle is found every plant on average until plants have
5 true leaves. After this growth stage an application should be made when populations
reach 4-5 beetles per plant on average. Cucumber beetles are known to migrate into
fields quickly, which warrants frequent scouting. This is especially important after
an insecticide application is made, as re-infestation at densities above threshold
is possible in only a few days.
Many insecticides can be used to manage cucumber beetles, but considering that most
can flare aphids, scout to make sure applications are necessary. Effective insecticides
include pyrethroids (IRAC 3A - bifenthrin, lambda cyhalothrin, etc.), neonicotinoids
(IRAC 4A - imidacloprid, acetamiprid, dinotefuran, thiamethoxam, and clothianidin),
carbamates (IRAC 1A - carbaryl), and organophosphates (IRAC 1B - malathion). Neonicotinoids
such as imidacloprid and dinotefuran can also be applied as drip applications and
may provide some aphid and squash bug suppression. If you didn’t use a neonicotinoid
drip application at planting and are seeing high numbers of cucumber beetles, I recommend
getting out an imidacloprid application (soil only) ASAP to help rotate effective
insecticide mode of action (MOA – IRAC Code). If populations are excessive, use a
knockdown foliar insecticide even when you still expect protection from a systemic
drip applied insecticide.
Fig. 1 – Spotted and striped cucumber beetles. Photo courtesy of Ric Bessin, Univesity of
Kentucky Entomology.
Fig. 2 – Bacterial wilt disease symptomology.
Squash Bugs Like cucumber beetles, squash bugs are an issue as soon as plants are in the field
and can vector bacteria that cause cucurbit yellow vine disease, also known as yellow
vine decline (Fig. 3, 4, and 5) . Smaller fields are most susceptible, and numbers generally are the highest on field
edges and during fruit-set and bloom. Fields should be monitored at least once a week
and monitoring should be focused on the underside of leaves, at the base of plant,
and under fallen leaves where squash bugs often congregate. Adults are difficult to
manage and applications should target young nymphs or eggs. Apply an insecticide when
egg masses or nymphs are observed on every few plants. Effective insecticides include
pyrethroids (IRAC 3A - bifenthrin, lambda cyhalothrin, etc.), neonicotinoids (IRAC
4A - imidacloprid, acetamiprid, dinotefuran, thiamethoxam, and clothianidin), and
carbamates (IRAC 1A - methomyl). Neonicotinoids such as dinotefuran and imidacloprid
(soil only) can also be applied as drip applications and may provide some aphid and
cucumber beetle suppression.
Fig. 3 – Squash bug adult pictured on a summer squash leaf.
Fig. 4 – Squash bug eggs pictured on top of a pumpkin leaf.
Fig. 5 – Yellow vine disease symptoms pictured on a pumpkin plant in Arkansas.
Melonworm Melonworm, Diaphania hyalinata , is a pest of pumpkins that feeds just under handles and etches the rind of pumpkins.
There is a lot of confusion as to what pest species we are seeing in Arkansas pumpkins
with names such as “rindworm” or “pickleworm” being used. Pickleworm is a different
species, Diaphania nitidalis , and not one that we will talk about much considering it is less common. Much of
this confusion comes from the sporadic nature of this pest and how quickly damage
can sneak up on growers.
Melonworm is a tropical moth species (Fig. 6) which migrates to Arkansas from coastal regions in August-October, with arrival times
varying from year-to-year which makes timing of management very difficult. Larvae
are green caterpillars with two longitudinal, white stripes down their back (Fig. 7). Larvae will quickly defoliate leaves of pumpkin plants and leave a “skeletonized”
appearance with only the leaf veins remaining (Fig. 8). You can often find larvae hiding under rolled, or turned pumpkin leaves as seen in
fig. 8. Melonworm larvae can quickly burrow into the rind of the pumpkin and under
the stem/handle which causes the stem to fall off (Fig. 9). Feeding on the rind results in the fruit ultimately becoming unmarketable.
Melonworms don’t overwinter in Arkansas so its arrival each year depends on the climatic
conditions for the year. In 2021 moths showed up much earlier than previous years
and began multiplying rapidly before pumpkin harvest started. Significant damage was
easy to see at many commercial pumpkin operations across Arkansas by late September.
The occurrence of moths should be an early sign for growers that an insecticide application
may be necessary. If growers can easily find these white and brown moths flying in
plantings, or are seeing larvae on leaves, a pesticide application will be necessary.
A threshold for this pest doesn’t currently exist and research in Arkansas Is ongoing.
Many effective products for melonworm are available but effective residual control
for each product will lead to more or less favorable results. Caterpillar specific
products containing chlorantraniliprole (IRAC 28 - Coragen), cyantraniliprole (IRAC
28 - Exirel), or cyclaniliprole (IRAC 28 - Harvanta) will offer the longest residuals
and should provide at least 21 days of residual control. Other caterpillar specific
products such as spinetoram (IRAC 5 - Radiant) and methoxyfenozide (IRAC 18 - Intrepid)
and also broad-spectrum insecticides such as pyrethroids (IRAC 3A - bifenthrin, lambda
cyhalothrin, etc.) will provide around 1 week of control. These insecticides should
be reapplied in 7 days if moths or larvae are still being observed.
Fig. 6 Melonworm moth on a mature pumpkin. These moths are easily observed on fruit or leaves
during daytime hours and are easily disturbed.
Fig. 7 – Melonworm caterpillars present on the underside of a pumpkin leaf. These larvae
can be identified by their green color and the two white stripes on their back.
Fig. 8 – Feeding damage caused by melonworm which is usually characterized by “skeletonized’
leaves that only have veins remaining (pictured right) or by rolled leaves (pictured
left).
Fig. 9 – Melonworm larvae feeding just under the handle/stems of pumpkins. Look for webbing
or excrement, as shown in this picture, as an indication that larvae are feeding underneath.
Aphids Melon aphid, Aphis gossypii , is considered a secondary pest in Arkansas pumpkin production. Insecticides such
as pyrethroids, pyrethrins, carbamates, or organophosphates that are used to control
cucumber beetles, squash bugs, and other pests, kill the natural enemies that usually
keep aphids suppressed. If you have used broad-spectrum insecticides in your pumpkin
patch this year, including many organic options, then you need to be scouting for
aphids (Fig. 10). There are many product options for aphid control such as acetamiprid (IRAC 4A- Assail,
Tristar, and Anarchy), flupyradifurone (IRAC 4D - Sivanto Prime), sulfoxaflor (IRAC
4C - Transform), and Flonicamid (IRAC 9C - Beleaf). Acetamiprid, sulfoxaflor, or flupyradifurone
are likely going to be the easiest products to find locally. Aphid control is necessary
when populations are building on every few plants and the natural enemy complex was
collapsed by recent broad spectrum insecticide sprays.
Fig. 10 – Melon Aphids on the underside of pumpkin leaves following a pyrethroid spray.
Management Plan Many of the insecticides mentioned here will control both cucumber beetles and squash
bugs, and in most production areas of the state, these pests are likely to be present
at the same time. Due to the risk of flaring melon aphids, a good strategy is to start
early with a drip application of imidacloprid (Admire Pro) or dinotefuran (Venom or
Scorpion) to prevent flaring aphids. These products usually give at least 3 weeks
of suppression that should help protect from bacterial wilt or yellow-vine disease.
Foliar applications of pyrethroids are usually relied on for cucumber beetle and squash
bug suppression, but it is important to rotate in other Modes of Action like carbamates, neonicotinoids, or organophosphates where possible. Repeated use
of one chemistry is likely to lead to lowered success of control. This is especially
important when considering squash bug, as it is difficult to suppress this pest once
infestations are excessive.
Melonworm is not likely to be a serious pest every year, but the losses we incurred
last year are a stark reminder that we need to be scouting every week beginning in
August. Rely on diamide products (IRAC 28) like Coragen or Exirel once moths or larvae
are observed in fields. A second application may be necessary in 21 days if pumpkins
still need to be protected.
