Squash Vine Borers Pest Guide

Squash Vine Borers share a lot in common with the Squash bug making it important to be familiar with both pests to have the best experience as a gardener growing squash.

The Squash Vine Borers are most dangerous as in the larval stage as they bore through the vining stem of your squash causing catastrophic damage. The damage they cause results in the blocking of water and nutrient flow necessary for the rest of the plant's survival and fruit production.

The best protection you have against these pesky borers is to invest in prevention measures. Preventative measures include scouting, post harvest removal, tilling, and covering. Till the soil in the fall to expose larvae to the elements and birds. During the growing season utilize row covers to prevent infestations.

How to Get Rid of Squash Vine Borers

  • Squash Vine Borer Distribution: Centralized throughout most of eastern and southern states
  • Squash Vine Borer Host Plants: Cucurbita maxima such as summer squash, winter squash, pumpkin
  • Squash Vine Borer Life Cycle: 12 weeks
  • Squash Vine Borer Eggs Per Lifetime: ~150-200
  • Squash Vine Borer Control: Spinosad, pyrthethrin, Bacillus thuringiensis, diatomaceous earth
  • Squash Vine Borer Predators: Parasitic wasps, birds, chickens
  • Most Common Vine Borer in North America: Common Vine Borer (Melitta cucurbitae)
Squash Vine Borer
Squash Vine Borer (Melitta cucurbitae)

What Do Squash Vine Borers Look Like?

After their reddish brown eggs hatch the larvae emerge with a tapered caterpillar shape. They are white with a brown head, 3 pairs of thoracic legs, 5 pairs of prolegs, and a hairy appearance. As it grows it develops a dark thoracic shield losing its hairy appearance and tapered shape. As larvae they grow from 1.5-2mm newly emerged to approximately 14mm long over a 4-6 week period.

Next they enter the pupae stage which lasts 14-30 days. As they sit 1-2 inches into the soil they develop a mahogany brown silk cocoon.

As adult moths they are attractive in appearance with their bright orange scales covering their body and wings with a metallic green or black sheen. Their hind wings are mostly clear creating a look similar to that of a wasp. Their bodies are about 16mm long with a wingspan of 25-38mm. In the field adults live for 3-5 days.

Squash Vine Borer Damage

The presence of Squash Vine Borers can be identified by green or orange sawdust like damage near the base of affected plants. Damage may first start appearing in early summer.

As the borers burrow through the stems of the plant they leave yellow brown excrement that is pushed through the holes created in the side of the stems entered.

At these points you can observe either part of the plant wilting.

In this case you should remove and dispose of the affected portions in an effort to save the rest of the plant from infestation.

Squash Vine Borer Damage
Squash vine borer damage to vine

In cases of the whole plant experiencing wilt you should turn to other control methods. If you notice the base becoming mushy or rotting away, act quickly as an infestation left untreated may lead to the plant collapsing and death.

What Do Squash Vine Borers Eat?

Squash Vine Borers are appropriately named as their diet is mostly limited to squash vines, especially those with large hollow stems. They can eat the fruit of the squash plants too, however they tend to stay strictly to the vine.

They will mostly eat plants of the genus Cucurbita with few exceptions, specifically they love summer and winter squashes along with pumpkins.Butternut, cucumbers, and melons are less often affected but should also be checked for damage. If you are planting a large crop of less susceptible varieties you may want to consider also planting a boundary crop.

Planting commonly affected squash around your main crop will make it easier to measure borer populations and reduce the risk of them going for your main crop.

Squash Vine Borer Eggs

Squash Vine Borer Eggs
Squash vine borer eggs in soil

The female Squash Vine Borer starts laying eggs only one day after its adult emergence.

Through its lifetime the female will lay 150-200 eggs on the lower part of the main stem, leaf stalks, leaves, fruit buds, and cracks in the soil near the base of the host plant.

The eggs appear as a flattened ovoid shape and dark to reddish brown in color. They measure about 1mm long and 0.85mm wide.

Many insects bury their eggs at the roots base to provide both food and protection when hatched. Eggs may be difficult to find at the base of a host without completely uprooting the plant.

How To Get Rid of Squash Vine Borers

Because Squash Vine Borers are so difficult to get rid of an integrated approach is best. The first control method that should be used if a population is already present is physical removal.

Cut out wilting stems as these have larvae damage. The next step is to either spray or inject Bacillus thuringiensis in the evenings. Because it can quickly degrade in the sun, frequent reapplication is needed.

Another frequently used pesticide is Spinosad which lasts longer requiring less applications. It is especially important that Spinosad be applied in the evenings after common bee flight times to allow proper drying.

It is important to be aware of how these pesticides can affect pollinators if not properly applied. Remember to always follow directions as listed on the label.

Squash Vine Borer Treatment

How to Get Rid of Squash Vine Borer
Sprays and treatments for squahs vine borers

  • Bacillus thuringiensis (Bt) - Store bought spray consisiting of natural soil-borne bacteria
  • Beauveria bassiana Spray - Natural fungi proven effective in treating many small garden pests
  • Spinosad Spray - Natural soil bacteria effective in treating several garden pests
  • Pyrethrin Spray - Natural chemical extract and pesticide from the genus Chrysanthemum
  • Carbaryl Baits - Dry granule insecticide used for many small pests
  • Diatomaceous Earth - Popular treatment from a wide variety of garden pests
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