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by Aaron Cato - September 28, 2020
Following mild winters we expect to see increased risk of tropical pests that are
known to move north throughout the summer. This risk is usually greater in the southern
portion of Arkansas, but with active flyers like moths, it often means we get infestations
throughout the state. Pickleworm and melonworm are two closely related species that
often pose a high risk to Arkansas cucurbits grown in the early Fall. Most growers
in Arkansas could tell you a story about a year that they saw significant losses from
a “melon”, “rind”, or “pumpkin” worm, but these occasional tropical pests are difficult
to prepare for on a yearly basis. Considering that we have already gotten calls from
South Arkansas where pickle worm is damaging summer squash, and that we’ve observed
melonworm in Western Arkansas, growers and agents need to be on the lookout for these
Pickleworm, Diaphania nitidalis, can damage a wide variety of cucurbit crops but prefers summer squash, winter squash,
and some pumpkins. This pest has also been known to damage cucumber and cantaloupe,
although they are not preferred. Pickleworm larva feed on the blossoms of these crops
but will often move from blossoms to tunnel inside of fruit (Picture 1). Tunneling
from the larva makes fruit unmarketable and can also lead to secondary disease infections.
Larva will also feed on the rind of some non-preferred hosts such as cantaloupe.
Pickle worm is incredibly difficult to scout before damage is observed as moths are
small, lay hard to find eggs at night, and are not attracted to light (Picture 2).
When considering that this is an occasional pest, a sound IPM plan for this pest is
difficult to achieve. Pickleworm larva are killed by a variety of pesticides such
as pyrethroids (Bifenthrin, Mustang Maxx, etc.) which are commonly used for other
pests. The issue comes with timing pyrethroid sprays to kill young pickle worm larvae
before they move inside of flowers or fruit. Selective products such as the spinosyns
(Radiant or Entrust), diamides (Coragen, etc.) or insect growth regulators (Intrepid)
will do a better job with control and provide increased residual.
Picture 1. Pickle worm larva feeding on pumpkin. Photograph by Thomas Kuhar.
Picture 2. Pickleworm moth. Photograph by John L. Capinera, University of Florida.
Melonworm, Diaphania hyalinata, also only feeds on cucurbits but primarily feeds on the foliage of the plant. Larvae
are often found in rolled up leaves where they spin silk to create a small shelter
(Picture 3), and moths are easily identifiable by their distinct coloration and can
be observed flying throughout the morning (Picture 4). Damage from this species is
easy to identify by the presence of untouched leaf veins with the foliage eaten between.
Melonworm is considered only a minor pest in Arkansas because it rarely gets to exceptionally
damaging levels on pumpkins early in their development. However, following mild winters
they can still be a large issue in late squash or other cucurbit crops. Melonworm
is controlled by pyrethroids (Bifenthrin, Mustang Maxx, etc.), spinosyns (Radiant
or Entrust), diamides (Coragen, etc.), or insect growth regulators (Intrepid).
Picture 3. Melonworm larva observed at Kibler, AR.
Management of Pickleworm and Melonworm
Pickleworm is known to cause large levels of damage to pumpkins and late squash crops
in Arkansas. Growers should always be on the lookout for this pest when we get into
August and should pull the trigger on pesticides as soon as damage to flowers are
observed or if other growers are finding this pest within the state. Pyrethroids used
for cucumber beetles or squash bugs will provide control but the timing must be right,
and applications need to be at least every 5-7 days. Selective products such as Coragen
are preferred because they will not flare aphids and they provide 14 or more days
of residual. We’ve seen many growers in the state try to use pyrethroids to manage
pickleworm and be very disappointed with results. They are often forced to swap to
diamides to try to cleanup infestations. Melonworm is much easier to manage and control
may not be warranted when infestations occur in mature pumpkins crops where loss of
some foliage won’t hinder fruit production. Checkout the Southeast vegetable guideand the MP144 for product recommendation.
Give me a call at 479-249-7352 if you think you have either of these pests or if you
have any questions at all.