NEIGHBORHOOD GARDEN FOR JULY 9, 2016
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SQUASH VINE BORER
BY
GEORGE EDGAR
If your zucchini, squash, pumpkins
or other vining crops (Cucurbits) wilt in mid to late July, an insect
called the squash vine borer may be feeding on your plants. Look at the
base of the plant for a hole or brown sawdust like insect droppings
called “frass”. If you see this,
split the base of the stems open with a very sharp knife or razor blade
and you can see a plump, cream colored caterpillar with a dark brown
head. You may also see frass
inside the hollowed vines.
Or, you may see brown “frass” pushed out from the stem by this feeding
larva that looks like a small grub.
Squash vine
borers overwinter in the soil and will emerge through July as day
flying, wasp like moths. They lay brownish-red eggs at the base of young
plants near the soil line and undersides of vining stems from June
through August. In about a
week, larvae hatch from eggs and immediately bore into stems to disrupt
water and nutrient flow.
Infested plants lack fruit, wilt and die. Damage occurs from July
through August.
If it is early
in the season you may keep the moth from laying eggs
on the plant by covering the
vines with some type of floating row cover. Remove the row cover when
the plants begin to blossom so other insects can pollinate the blooms.
If you use
chemicals in your garden, insecticides with Permethrin (Eight), Carbaryl
(Sevin), Malathion, Bifenthrin, or Rotenone can be used if applied early
in the season and reapplied every seven to 10 days. Bt (Dipel) works
only if injected into the stem with a syringe as the worm does not eat
on the outside of the stem. CAUTION: Some insecticides, applied under
conditions of high temperatures (above 80 degrees) and high humidity,
may injure or burn plant foliage.
Also it is best to avoid dust formulations on plants that are in
bloom as the dusts are more toxic to beneficial insects that are needed
to pollinate the plant, especially bees.
Spraying in late evening after the beneficial insects have gone
to bed will reduce injury to pollinators.
Once you
discover the borer problem and the plant starts to wilt, insecticides
will not work. Sometimes,
you can save the plant by splitting the stem with a razor blade starting
where the borer entered and working up. Then remove or destroy the worm
by hand, and then cover the vine with moist soil and water well. You
might be able to save the plant this way.
For butternut
squash, acorn squash, and vine crops such as pumpkins, and watermelons
where the fruit sets on the end of a long vine, cover the vine and
leaves with soil about every 3 or 4 feet.
New roots will grow under the mound and if a borer gets in at the
base of the plant, you might be able to save the rest of the plant by
cutting off the damaged section. I water my squash with soaker hose and
try to lay the vine along the hose.
If your plants
are wilting, and you cannot find any squash vine borer activity, there
may be other causes. A disease
called bacterial wilt often affects vine crops, especially cucumbers.
This disease is carried by the cucumber beetle so pick off the
insect, destroy any eggs on the top or underside of the leaves, and
spray with Permethrin (Eight), Malathion, Carbaryl (Sevin), Bifenthrin,
or Rotenone. Use a sticker-spreader such as Turbo so the insecticide
sticks to the leaf and does not wash off easy. It is best to spray in
the evening about sundown, after the beneficial insects have gone to
bed.
For more information contact your local County Extension Office
or go on the internet to:
http://ianrhome.unl.edu/search. In the top box scroll down to
Extension. In the bottom box type in “squash vine borer” (use quotation
marks), or the number of the publication, or the disease or the insect
you want information about. These NebGuides or NebFacts, or other
publications can be printed from your computer.
(This article
was developed from InfoSource material prepared by the University of
Wisconsin-Extension, and from publications of the University of
Nebraska-Lincoln, Department of Entomology, and the University of
Nebraska-Lincoln Extension Service.)
Copyright 2016 |