The squash vine borer-- scientific name (Melittia cucurbitae). AKA-- well... can't say that in polite company! Here's a pic!
Adult squash vine borer-- Figure credit: Brian Caldwell, Cornell University
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The adult squash vine borer is an orange and dark grey moth with hairy back legs and clear wings with black markings. Unlike most moths-- which are active at night-- the squash vine borer is active during the day. It's kinda long and narrow and is often mistaken for something else-- 'cuz it doesn't even look like a moth.
The adult squash vine borer is an orange and dark grey moth with hairy back legs and clear wings with black markings. Unlike most moths-- which are active at night-- the squash vine borer is active during the day. It's kinda long and narrow and is often mistaken for something else-- 'cuz it doesn't even look like a moth.
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The pupae overwinter underground about an inch beneath the surface. They emerge as adults and lay eggs at the base the squash vines-- usually about an inch or two above the ground. The eggs hatch and the larvae get right to work-- boring into the vine stems. They work their way to center of the stem and eat their way up the vine.
The adults are very attracted to the yellow flowers of the cucurbit family-- that yellow color is their 'bullseye'! They hone in on that color! They usually don't bother cucumbers and melons-- and if you look at the flowers you'll see that the yellow color isn't as rich and intense and, of course, the flowers are MUCH smaller.
The adults are very attracted to the yellow flowers of the cucurbit family-- that yellow color is their 'bullseye'! They hone in on that color! They usually don't bother cucumbers and melons-- and if you look at the flowers you'll see that the yellow color isn't as rich and intense and, of course, the flowers are MUCH smaller.
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Cucumber and squash blossoms
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Yellow summer squash (cucurbit pepo) is a prime target-- think MORE YELLOW to attract them-- the flowers AND the fruit are yellow-- and they have succulent stems. But the squash vine borer moth will be attracted to the bright yellow flowers of any squash.
In its larvae form the squash vine borer is a cream-colored caterpillar with a dark brown or black head. Ugly-- don't cha think?
In its larvae form the squash vine borer is a cream-colored caterpillar with a dark brown or black head. Ugly-- don't cha think?
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The infamous squash vine borer larvae
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When newly hatched it's tiny, almost translucent, and hard to see. They'll grow to as big as an inch long and they look like a segmented grub.
A single moth can lay up to 250 eggs! YIKES – no wonder they can do so much damage! The eggs are reddish brown, kinda flattened and tiny-- like 1 mm! Unlike squash bugs, whose eggs are laid in clusters on the underside of the leaves, the squash vine borer's eggs are laid individually--not in a group, making them harder to spot.
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The damage is done as the larvae bore in and reach the center of the vine, where they disrupt the flow of water and nutrients up the stem of the plant and essentially cut off the supply. If your plant suddenly begins to wilt-- that's an almost sure sign of this pest. Untreated, it'll cause the plant to die.
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Prevention is the best strategy
Here are our top 13 strategies for combatting this pesky pest-- starting early in the season and progressing through.
Here are our top 13 strategies for combatting this pesky pest-- starting early in the season and progressing through.
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1) If this is a pest you battle every year, use a lightweight row cover, like Agribon 15, as an insect barrier when you plant. It weighs .45 oz per square yard and allows 90% light transmission. Agribon 19 can also be used; it weights .55 oz per square yard with 85% light transmission. Lay the row cover over the rows with or without supports (hoops or rods, etc.). You gotta make sure the cover's bottom edge is securly fastened to ward off insect intrusion. The row cover will need to be taken off as soon as the plants start to flower-- because the flowers are insect pollinated! (I know-- this is a little late for this year but something to consider for next!)
2) Be on the lookout for the adults-- make notes about when you first see them, so you know when to start watching and checking for eggs-- your future self will thank you! (Again, a little late for this year but keep this in mind for next year!)
3) Get the source-- seek and destroy adult squash vine borer moths. Learn to be able to recognize and spot them. Lay a piece of board or heavy cardboard near or under the squash vines. The adult moths crawl under them for warmth at night and can easily be destroyed in the early morning. Also, look for them in the early morning or at dusk under the squash leaves. Crush or drop any you find in soapy water. A dead moth won't be laying any more eggs.
2) Be on the lookout for the adults-- make notes about when you first see them, so you know when to start watching and checking for eggs-- your future self will thank you! (Again, a little late for this year but keep this in mind for next year!)
3) Get the source-- seek and destroy adult squash vine borer moths. Learn to be able to recognize and spot them. Lay a piece of board or heavy cardboard near or under the squash vines. The adult moths crawl under them for warmth at night and can easily be destroyed in the early morning. Also, look for them in the early morning or at dusk under the squash leaves. Crush or drop any you find in soapy water. A dead moth won't be laying any more eggs.
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4) Cut a 4” x 6” piece of yellow cardboard— the same color as the squash blossoms. We've use a bright yellow colored file folder, that closely matched the yellow of the squash blossoms—close enough anyway! Cut a piece and secure it to a stake. Put on some gloves and coat the yellow cardboard with ’Tree Tanglefoot' (see the notes below)-— super sticky stuff that does what its name implies. It basically will trap the bugs— like fly tape. To make the trap more attractive— lightly crush a squash blossom and stick it to the cardboard. (Bugs are attracted to wounded plants-- a sign of weakness; they'll attack those plants.) Then put some ’tangle trap’ on that too-- but not on the whole thing or they won’t ’smell’ it.
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5) Wrap the plant stem with panty hose or tin foil to keep the moth from laying eggs on the stem. You need to start just beneath the soil and wrap up to just below the lowest leaf. Even if you use this strategy, continue checking for eggs on the rest of the stem and leaf stems-- especially the lowest exposed areas.
6) Get into a routine of continually checking at the base of your plants for eggs. Brush the eggs off into a small dish of soapy water or squish 'em. Getting them before they hatch and burrow into your vine is much easier!
6) Get into a routine of continually checking at the base of your plants for eggs. Brush the eggs off into a small dish of soapy water or squish 'em. Getting them before they hatch and burrow into your vine is much easier!
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Spotting an egg of the squash vine borer! REMOVE & DESTROY!!
7) Check around the base of your plant for what looks like crumbly sawdust. It's called frass in polite company-- AKA-- vine borer SH_ _ . If you see yellow frass coming from the stem near the base of the plant, it's almost certain that one of those little critters bored into your plant. Check your plants frequently for signs of frass and act quickly if you find it. Frass means the borer is already inside your squash stems! Find the entry hole.
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Entry hole of the squash vine borer!
8) Remove any borer that burrows into your vines. HOW? Plant Surgery! The frass will be next to the borer's hole. (The frass had washed away in the rain.) You'll need a tweezers and a sharp knife-- like an Exacto knife (ideal) or small bladed kitchen knife. Carefully slit the vine longwise-- not across but along the length. Gently pry the vine open enough to see inside. You'll see the hole the borer made in the center of the stem and his ongoing trail of frass-- in one end and out the other as it munches away. Keep following the frass trail up the vine until you find the culprit. Remove it with a tweezers and destroy the borer-- drop it into soapy water or squish it. Check closely for multiple borers-- not likely but possible.
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Extracting the squash viner borer with an Exacto knife and tweezers.
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Follow-up to surgery: Gently pinch the vine back together as much as possible. Cover the slit stem with moist soil to encourage rooting and healing. Sprinkle a layer of dry soil over the moist soil-- to help shield the moist soil from the sun and hold in the moisture.
9) Encourage the plant to put down more roots-- in case the main stem gets infested and compromised. Simply find a node (the place where leaves emerge from the stem) and cover the vine with a thick layer of soil on both sides of the node-- a length of about 4-6 inches. The vine will react by sending out auxiliary roots from the node. Champion pumpkin growers do this-- covering many nodes along the length of vines to encourage lots of rooting. This is a great strategy for increasing your crop production AND as a backup root system as insurance against the main stem going down squash vine borers. At least you won't loose THE WHOLE plant! (Also great insurance against wind, hail and drought. More roots = more resilience!)
10) Use Bt (Bacillus thuringiensis)-- a naturally occurring bacteria that's deadly to caterpillars. Their digestive system can't handle it! The bacteria doesn't affect us-- but it's deadly to caterpillars. Using the liquid form (we suggest Monterey B.t.; see notes below) with a syringe. Inject the Bt into the stem near the base-- an inch or two above the ground. When the borer burrows in and starts eating it'll die before it can grow and do much damage. Note that once the borer is inside the squash stem, they are well protected from insecticides sprayed on the outside of the plant. However, if you see frass and know there's a borer in your plant-- you could inject Bt at multiple intervals and kill it. Repeat the injection every 7-10 days to maintain effective control.
11) Rotate your crops. Ideally, you shouldn't replant cucurbits in the same place for at least three years. After you harvest in the fall and before freeze-up, lightly disturb the soil about 1 inch deep. This'll expose the pupae to winter weather and predators-- reducing the numbers of adults that emerge in the spring.
12) If your plant dies, remove it from the garden, inspect and dissect it before you add it to your compost pile. Find the borer(s) that did this. Also, look closely for any unhatched eggs.
13) Keep your plants healthy and strong with adequate water and nutrients. That'll go a long way in helping them deal with any attacks, while you work to defend them!
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These are our best tips for dealing with these critters. We sincerely hope you found this information useful! Good luck out there!
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Our best to you,
Theresa
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Links to products-- please note these are affiliate links. At the time of this posting both of these products are OMRI listed, labeled, and approved for use in organic gardening.
Monterey B.t.: https://amzn.to/477EJeC
Tree Tanglefoot: https://amzn.to/3YaIRGB
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