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by Aaron Cato and Ryan Keiffer - April 10, 2023
Squash vine borer, Melittia cucurbitae, is an insect pest of winter squash, summer squash, pumpkins and other cucurbit crops
in Arkansas. Infestations often go unnoticed until signs of insect boring or wilted
plants are noticed in the midsummer. Nothing can be done once squash vine borer inhabit
plants, but there are many tactics that can be employed to prevent damage by this
Squash vine borer (SVB) is a day-flying clearwing moth species from the family Sessiidae,
similar to many other “boring” pests like raspberry crown borer or peachtree borer
(Figure 1). SVB overwinter as pupae or larvae just a few inches below the soil surface. They
finish pupation in the spring as it begins to warm up and then have an extended emergence
as adult moths that may last a few weeks. In Arkansas we have two generations per
year of SVB, which means that growers face risk of infestations from May-September.
Soon after emergence, SVB females mate and quickly begin laying eggs on the underside
of cucurbit stems, leaf stalks, and near flowers (Figure 2). SVB eggs are shaped like flat disks, are copper colored, laid singly and shouldn’t
be confused with squash bug eggs which will be more upright and laid in groups. SVB
eggs hatch in 6-11 days and larvae will then immediately begin to bore into the stem1. Larvae will then feed for 14-30 days before exiting the stem and pupating in the
soil (Figure 3).
Figure 1 - Squash vine borer adult moth. Photo by Ansel Oommen, Bugwood.org
Figure 2 - Squash vine borer eggs laid on the stems of a squash plant. Also pictured in a new
entrance hole with frass around the entrance, which is often the first sign after
finding eggs of a new infestation.
Photo by Aaron Cato
Figure 3 - Squash vine borer larvae observed feeding in a squash stem. Photo by Aaron Cato
Squash vine borer (SVB) larvae burrow into the stem or crown of cucurbit plants where
they feed on the surrounding plant tissue and hollow out a small section of the plant
and destroy xylem and phloem structures. This feeding will present as wilting in the
region of the vine that has lost its water and nutrient resources and can eventually
progress to complete collapse in those plants (Figure 4). Frass can generally be found around greenish holes near the base of wilting plants
and will often appear as a mushy tan/green substance (Figures 2 and 5). These holes will eventually rot and it’s possible that multiple larvae can attack
a single plant, contributing to its collapse.
Figure 4 - Wilting in cucurbit caused by squash vine borer larvae. Identification of squash
vine borer damage can only be confirmed if bore holes or frass are observed on wilting
plants. Photo by Aaron Cato.
Figure 5 - Feeding damage by squash vine borer larvae. Frass from larval feeding can be seen
here around an exit hole present on a pumpkin runner. Photo by Aaron Cato.
Squash vine borer (SVB) is a native pest that co-evolved with cucurbit plants native
to North and South America that we now grow as crops2. SVB prefer crops within the genus Cucurbita and prefer cultivars from the species of Cucurbita pepo (winter squash, summer squash, pumpkins, and zucchini) and Cucurbita maxima (buttercup squash, banana squash, hubbard squash, and others). Common cucurbit crops
that are generally unaffected by SVB are watermelon (Citrullus lanatus), cucumber (Cucumis sativus), and cantaloupes (Cucumis melo). Cucurbit crops that are more vining in nature and with runners that are smaller
in diameter are generally affected less as they are less hospitable for larvae.
Squash vine borer (SVB) management can only be successful if larvae are controlled
prior to entering the plant. Adult monitoring is one of the easiest ways to determine
when plants are at risk. Adults begin to emerge at 750-1000 degree days (base 50F
degree day model with a January 1st biofix) which is usually in May in Arkansas3. Pheromone traps utilizing SVB lures should be set up near susceptible cucurbit crops
to determine when adults are emerging and when egg-lay is beginning. A Heliothis trap is usually the most cost-effective solution to trapping for trapping SVB (Figure 6)4. See FSA7090 “Using Pheromone Traps to Monitor Pests in Tomatoes and Cucurbits” for information
about trapping for SVB. Squash vine borer eggs are also a useful monitoring tool and
should be scouted for after reaching 750-1000 degree days. These eggs are often found
on the underside of stems, leaf stalks and near flowers. Additionally, growers should
look for the first signs of frass that indicate early infestation of vines before
the majority of larvae enter plants (Figure 2).
Figure 6 - Pheromone trap set up for squash vine borer using a Heliothis trap. Photo by Ryan Keiffer.
There are a number of cultural or mechanical controls that can help to reduce the
impact of squash vine borer (SVB). First, areas where cucurbit crops are planted should
be rotated each year. Squash vine borer adults will emerge in the area where susceptible
cucurbits were planted the year prior, so moving plantings will help create some distance
from moths and susceptible crops. Additionally, field sanitation and cultivation should
be maximized immediately after harvest. Vines should be removed from the planting
and then discarded or plowed under immediately after harvest is completed, or when
infested plants are found. The goal is to keep larvae from pupating in the top of
the soil and completing their life cycle to reduce infestation pressure. Plowing after
harvest is also very useful to disrupt the life cycle of this moth species, as late-stage
larvae and pupae will either be displaced or killed when the soil is turned.
Host plant resistance is a key aspect of any integrated pest management (IPM) program
and should be utilized to help avoid the impact of SVB. Resistant cultivars derived
from C. moschata or C. mixta should be prioritized whenever possible. Variation within susceptible species also
exists and some cultivars from C. pepo such as summer crookneck are known to be less susceptible than others5. Host plant resistance is especially important for areas that have known issues with
SVB or if crop rotation is limited due to lack of space.
Perimeter trap cropping with highly attractive cucurbit crops is a useful tool to
help prevent SVB infestations5. Blue hubbard squash is highly attractive to many pests of cucurbits (SVB, squash
bugs, cucumber beetles, etc.) and can be planted around the perimeter of the field.
The outside rows of plantings and the first 1-2 plants on the front and back of each
row should be planted with a highly susceptible planting. These perimeter plants should
be sprayed often to kill larvae as they emerge, and infested plants should be destroyed
before larvae can exit and pupate. This strategy works best when a less attractive
cucurbit crop is surrounded by a highly attractive cultivar like blue hubbard, and
when the trap crop constitutes less than 10% of the planted field.
Row covers consisting of a lightweight, permeable cloth can be used to prevent SVB
infestations. This is often very time consuming, expensive and can be tricky to implement
while also not affecting insect pollination6. Squash vine borer are day flying moths and lay eggs at the same time that many pollinators
are visiting flowers. Row covers should be removed in the evening and replaced in
the early morning to allow some pollination via squash bees. Row covers can also be
placed after 50% of plants have flowers if SVB moths aren’t active yet, which often
leads to no yield loss. Row cover use is most viable for very small plantings due
to the increased labor needs.
Insecticides are often a necessary tool to prevent severe damage from squash vine
borer (SVB), but should be used at all times alongside cultural controls such as sanitation,
plowing and host plant resistance where possible. Insecticide spray schedules should
be avoided at all times to help protect beneficial insects. Many predators and parasitoids
can help to suppress SVB and spray schedules have not been found to yield more fruit
than threshold based systems. A variety of thresholds exist in the literature for
SVB adult moths, but it can often be very difficult to consistently capture adult
moths in traps in Arkansas. Instead, insecticidal control of SVB should be considered
based on a combination of monitoring techniques, field history, and the cultivar being
Degree day modeling and pheromone traps should be used together to determine if SVB
have emerged in the immediate area, and whether plants are at risk for infestation.
The risk of infestation usually begins in the early season when plants begin to run
but can be harder to gauge in later plantings. The attractiveness of the cultivar
being grown5 and the history of the field should also be considered. If a highly attractive cultivar
is being grown in an area with past issues, an insecticide application is going to
be necessary. Field scouting should also be used to determine if moths are actively
laying eggs in plantings. The presence of eggs or even any amount of frass is a good
timing for an insecticide application in a very attractive cultivar, but infestation
density should be considered in non-attractive cultivars. Use these factors in combination
following the first signs of adult moths, eggs or even the first signs of frass on
stems or runners (depending on whichever is found first) to target insecticide applications.
Insecticide application timing and frequency depends on the material that is being
used. If an insecticide with a short residual such as a pyrethroid (bifenthrin, lambda-cyhalthrin,
esfenvalerate, etc.) or a spinosad based product is being used, two insecticide applications
are needed when a treatment decision is made. Squash vine borer eggs are resistant
to insecticides and take 6-11 days to emerge. This means that two insecticide applications
will be necessary 7 days apart to ensure that the insecticide will be effective when
larvae emerge, as many insecticides only have 4-5 days of effective residual control.
However, insecticides in the diamide chemical class that contain chlorantraniliprole,
cyantraniliprole or cyclaniliprole have a longer residual and would likely only necessitate
Pyrethroids are commonly used for control of squash bugs and cucumber beetles and
are effective at controlling SVB. Monitoring should continue each week and additional
insecticides should be considered 21 days after the initial treatment decision or
7 days after any other insecticide applications for other pests depending on their
effectiveness for SVB and what you are observing via monitoring. See the Southeastern U.S. Vegetable Crop Handbook for more information regarding insecticide efficacy8.
All insecticide applications for SVB should be applied in the late evening to avoid
impact on pollinators. Cucurbits need insect pollination to set fruit and insecticide
applications during peak pollination can lead to significant yield loss. Insecticide
applications should target the base of plants and good plant penetration is needed
to cover susceptible stems and runners. Blower sprayers will get the best penetration
and coverage but may not be necessary if directed applications can be made on a smaller
scale directly to where eggs are generally laid.
1Middleton, E. 2018. Biology and Management of Squash Vine Borer (Lepidoptera: Sesiidae).
Journal of Integrated Pest Management 9: 1-8.
2Howe, W. L., and A. M. Rhodes. 1973. Host relationships of the squash vine borer,
Melittia cucurbitae with species of Cucurbita. Ann. Entomol. Soc. Am. 66: 266–269.
3Canhilal, R., G. R. Carner, R. P. Griffin, D. M. Jackson, and D. R. Alverson. 2006.
Life history of the squash vine borer, Melittia cucurbitae (Harris) (Lepidoptera:
Sesiidae) in South Carolina. J. Agric. Urban Entomol. 23: 1–6.
4Jackson, D., R. Canhilal, and G. Carner. 2005. Trap monitoring squash vine borers
in cucurbits. J. Agric. Urban Entomol. 22: 27–39.
5Seaman, A. 2013. Biology and management of squash vine borer in organic farming systems.
6Minter, L. M., and R. T. Bessin. 2014. Evaluation of native bees as pollinators of
cucurbit crops under floating row covers. Environ. Entomol. 43: 1354–1363.
7Brust, G. E. 2010. Squash vine borer (Lepidoptera: Sesiidae) management in pumpkin
in the mid-Atlantic. J. Appl. Entomol. 134: 781–788
8Kemble, J.M. 2023. Southeastern U.S. 2023 Vegetable Crop Handbook. https://content.ces.ncsu.edu/southeastern-us-vegetable-crop-handbook