Squash Borer Moths Laying Eggs Until First Week of July and Beyond?!

Every year, we plant zucchini and other squashes.  Every year the Squash Borer Moth says "Thank you" and lays her eggs on their stems.  She does have preferences though.  Zucchini is a favorite.  Butternut is one of the last on her list.  For most of NY, start inspecting by June 20 when the moth begins emerging and laying her eggs on the stems of squash and zucchini leaves.

July 26, 2013 Colleen spotted a squash borer moth on the mystery squash in her plot.  Was it scouting to lay eggs? Or a hapless male just wishing?

Below is the colorful moth responsible for the borer.  She is Melittia cucurbitae who flies during the day and often is mistaken for a bee or wasp because of the way she moves, flying in a zig-zag pattern.  The wing span of the adult female squash-borer moth is 1 in. to 1½ in. with metallic green forewings.

Squash vine borer adults  – Photo: Jeff Hahn

Here a lone egg might be missed by even the most vigilant gardener.  Borer eggs are hard to spot.  They are tiny, (only 1/24 of an inch in diameter), shiny brown disks that the moth lays on the stems, underside of the leaves (shaded parts of the stems), and on the blossoms. An individual adult can lay from 150 to 250 eggs.  They hatch in about 1 week. 





This sprinkling of eggs is more detectable.

If you miss finding the eggs, they hatch and the tiny white, wrinkled larvae tunnel into the stem and feed, eventually causing the vine to wilt and die.  Feeding may continue for four to six weeks. A sticky gob of excrement (frass), which resembles wet sawdust, typically marks the entrance site.  If a vine dies before the borer has completed its larval cycle, the larva can migrate to a neighboring plant and resume feeding there.

The mature larva is a thick, white wrinkled 'worm' with a brown head, and is about 1 inch in length. 

Here the egg was allowed to hatch and the larva bore into the stem and began eating.  


PREVENT THE BORER MOTH from LAYING EGGS
The Piermont Community Garden has had Squash Borer infestation every year.  We may need to interrupt the cycle of this pest by not planting cucurbits (pumpkins, squash, cucumbers, and watermelon) for a year.  Plants must be protected from the first day they are planted outside.  For most of NY, start inspecting by June 20 when the borer moth begins emerging and laying its eggs on the stems of squash and zucchini plants. Talk to Carol Cameron who has been dealing with this pest in the Community Garden for 15 years. 

Here are some ways recommended to deal with the problem.  Some of these are not practical for our setup unless all the affected plots act in concert.  Close neighbors who also grow squash may need to participate for maximum effectiveness:

• Start a new crop in soil that is not infested with larvae from the previous year OR skip the planting of susceptible plants for a year OR move crops to a new location far from the infested site to interrupt the borer's life cycle.

• Destroy the moths in twilight or early morning when they are resting on the upper side of the leaf bases.

• Plant as early as the weather allows (May 15 if you've first warmed the soil in that spot) to stay ahead of the borers. Borers do not usually emerge until late spring or early summer (about June 20 in Rockland Co)

• Make a second planting of summer squash in early July.  It will mature after adult borers have finished laying eggs.

• Completely cover the plants with row covering and pin the edges securely to the ground so the moth cannot crawl underneath.  Keep the barriers in place for about two weeks after the first adult borer has been seen. Then, remove the cover to allow for pollination. NB: If plants are located where the cocoons are present from last year's planting, the moths will hatch under the row covering.

Some other strategies that you may wish to try:

• In 2009 kaolin clay was registered for home garden use in NYS for squash vine borer suppression. It is important to control larvae before they enter the stem, because once they enter the stem, insecticides have little effect. Direct the spray to the stems of the plants near the base. Begin prior to infestation (starting about June 20 for most of New York State) and apply every 5 to 7 days as per label instructions. This is a repellent and feeding deterrent and should be applied before the insect arrives. Spray on the transplants before setting them out. Reapply after rain. NOFA allows the use of this substance which is also used as a food additive and in toothpaste.

• Spray the stems and undersides of the leaves with Bt, or Bacillus thuringiensis as soon as the plants begin to grow. Continue spraying throughout the growing season. Bt is an organic-gardening approved pesticide and is not harmful to the bees which are so important for pollinating squash and many other vegetables.

• Wrap the base with tin foil during the early spring for the four or five weeks that borer eggs are hatching in your area to create a barrier to egg-laying moths..

• Wrap a 3-inch long piece of panty hose around the main stem at planting time to thwart the egg-laying.

• Place a small paper or plastic cup surrounding the base of a new plant like a collar

• Fill yellow cups with water to attract the moths.

• Plant varieties of summer and winter squash that are resistant or less prone to infestation (i.e. Waltham Butternut, Green Striped Cushaw, Summer Crookneck). Squash borer like from most preferred to least: winter squash (including Hubbard squash), summer squash, pumpkin, gourd, cucumber, and muskmelon.

• Reduce the number of borers for the next year. Remove vines as soon as the growing season is over to interrupt the life cycle of second generation larvae. Promptly pull and destroy any plants killed by squash vine borers.

SCOUT & REMOVE EGGS to PREVENT INFESTATION

• Look for the eggs by June 20. The eggs are laid near the base of the stem.  
• Remove them before they hatch. Smash or drop them into a vial of alcohol. Don't just brush them off to land elsewhere on the plant or the ground.   
• Mini lint rollers also work well for picking up the eggs.  
• The window for finding them is 7-10 days once they are laid and before they hatch & burrow in the stem..

RECOGNIZE A SQUASH VINE BORER INFESTATION
Begin scouting the garden in June.  Sites heavily infested last year are more likely to have infestations this year. 

The larvae are usually found in the lower 3 feet of the stem.  The telltale signs of squash vine borer infestation include:

• Stems which suddenly wilt, become soft and mushy, darken in color.
• Squash on the vine suddenly stop growing and the plant's production stagnates.
• Near the base of the stem, you see a build-up of what looks like orange sawdust (this is squash borer excrement)! 

TAKE ACTION TO DESTROY THE LARVAE AND SAVE THE PLANT

• Cover the vines at plant joints to encourage growth of secondary roots, which can support the plant if the main stem is damaged.
• Borers can be removed successfully from vines if they are detected early.  To do this, slit the stem with a sharp knife and remove the borer.  Cover the stem wound with moist soil above the damage to promote root formation.

NEXT YEAR

You may not be successful in preventing all larvae from reaching the soil and forming their cocoon.  As you prepare the soil in Spring for planting, look for squash borer pupae like the ones in this photo and destroy them before they morph into moth form.