We still haven’t observed any Melonworm in the state this year, but we are on the
lookout and will be posting on our pest scouting webpage , as well as 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 didn’t start off quite as hot this year with a mild late-June and that seems to
be more favorable for cucumber beetle. Luckily plants grew off quickly and avoided
the majority of bacterial wilt infection, but we’ve seen some locations where populations
have seemed uncontrollable. Squash bugs have also been out in full force although
they don’t seem to mind the heat too much. 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, issues
with squash vine borer and especially melonworm seem to make up most problems. See
our new fact sheet for more info on squash vine borer. Melonworm has been the most serious pest of pumpkins
in Arkansas in some years as widespread damage was observed across the entire state
and MidSouth in 2021. We don’t see those levels of damage every year and 2022 was
one of the lowest in the last few, but we need to be on the lookout for moths and
larvae to prevent major losses. Even in a low year we still observed significant damage
in our trial and there were growers who had to spray to prevent economic losses from
melonworm feeding.
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 (Pictures 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 a few 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). We’ve
seen some complaints with the pyrethroids we normally rely on, although no resistance
has been reported in this pest. I recommend choosing bifenthrin over other pyrethroids
as it usually offers the best control. 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. You may consider mixing
in another insecticide from a different MOA in foliar sprays if you feel like you
aren’t getting acceptable control.
Picture 1 – Spotted and striped cucumber beetles. Photo courtesy of Ric Bessin, University
of Kentucky Entomology.
Picture 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 (Picture 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.
Picture 3 – Squash bug adult pictured on a summer squash leaf.
Picture 4 – Squash bug eggs pictured on top of a pumpkin leaf.
Picture 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 (Picture 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 and 4
sets of prolegs (Picture 7 and 8). Larvae will quickly defoliate leaves of pumpkin plants and leave a “skeletonized”
appearance with only the leaf veins remaining (Picture 9). You can often find larvae hiding under rolled, or turned pumpkin leaves as seen in
Picture 9 . Melonworm larvae can quickly burrow into the rind of the pumpkin and under the stem/handle
which causes the stem to fall off (Picture 10). 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
(early September) and began multiplying rapidly before pumpkin harvest started. Significant
damage was easy to see at many commercial pumpkin operations across Arkansas by late
September. In 2022 only low numbers of melonworm were observed starting on September
19, and infestations were not widespread. 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 or Shenzi), 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 and may
offer less efficacy (Figure 1 ). These insecticides should be reapplied in 7 days if moths or larvae are still being
observed.
Picture 6 Melonworm moth on a mature pumpkin. These moths are easily observed on fruit or leaves
during daytime hours and are easily disturbed.
Picture 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.
Picture 8 – Melonworm larvae pictured on a pumpkin leaf. Melonworm have 4 prolegs which will
distinguish them from other caterpillars such as cabbage looper which are common on
pumpkin.
Picture 9 – 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).
Picture 10 – 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.
Figure 1 – Melonworm efficacy trial from 2022 in Alma, AR on pumpkins. An application of Lambda
cyhalothrin (IRAC 3A – pyrethroid) or Coragen (IRAC 28 – diamide) was made on 9/19
when melonworm moths and larvae were first observed and were compared to an untreated
control (UTC). The left y-axis corresponds to the bars and indicates the percent fruit
damage that was observed, while the right y-axis corresponds to the lines and indicates
the number of melonworm larvae observed in plots with 3 plants.
Aphids Melon aphid, Aphis gossypii , is considered a secondary pest in Arkansas pumpkin production (Picture 12) . 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 (Figure 2 ). 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. 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.
Picture 12 – Melon Aphids on the underside of pumpkin leaves following a pyrethroid spray.
Figure 2 – Average melon aphids present on squash plants in Hope, AR in 2022. Plants were
either untreated, sprayed weekly with a pyrethroid (Warrior II), or received an insecticide
based on pests that were present (scouting pyrethroid and coragen). Scouting based
plots received only 1 insecticide application and minimal aphids were observed. Plots
receiving weekly pyrethroids had excessive aphid numbers and a large amount of plant
stunting.
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
in 2021 are a stark reminder that we need to be scouting every week beginning in August.
Even in 2022 when populations were very low, we still observed significant damage
in our plots and on grower operations. Rely on diamide products (IRAC 28) like Coragen
or Exirel or Shenzi once moths or larvae are observed in fields. A second application
may be necessary in 21 days if pumpkins still need to be protected.
If you have any questions give me a call at 479-249-7352.
Aaron Cato
