Pest Profiles: The Squash Bug, Anasa tristis

The bane of many gardeners life, the squash bug, Anasa tristis, is commonly found throughout the US. Their damage is limited to members of the gourd family including squash, cucumbers, and pumpkins. They attack plants in large numbers and like to gather on the leaves, vines, and fruits of the plant. The bugs cause damage to the plants by injecting a toxin before they suck the sap out of it. The toxin causes the plant to wilt because the nutrients are no longer able to circulate to the leaves, causing them to turn black and brittle. Young fruit is destroyed by the bugs feeding on them. Large numbers of squash bugs on a plant can prevent the plant from producing at all.

How to Identify Squash Bugs

The squash bug has a brown or gray body and is about 1/2-inch long. They have flat backs, and the sides and underbelly have orange stripes. Their shells are hard and these destructive bugs can fly, too. Squash bug nymphs are 1/10-inch long and are gray with black legs. The eggs are laid on the underside of leaves and are yellow or bronze.

squash bug bugs

Source: Flickr User ilovebutter

Young squash bugs are whitish green with red heads and legs. They get progressively darker as they mature.

Life Cycle of the Squash Bug

The squash bug overwinters in sheltered places such as piles of leaves or under rocks. As soon as spring begins, they move to cucurbit plants to mate and feed. Female squash bug lays small clusters of eggs, about 20 at a time, on the underside of the leaves on the plant. They are laid between the veins of the leaf, forming a V shape. Eggs are laid from the end of May through to mid-summer and hatch within 10 days, and the juveniles then take up to six weeks to mature.

Juvenile Squash Bug

Source: Flickr User Robert T Bell



How to Control Squash Bugs

There are several different ways to control the squash bugs that attack your plants.

  • There are several varieties of squash plants that are resistant to the squash bug. Plant these types of plant whenever possible.
  • Hand-pick the squash bugs from your plants as soon as you spot them. Have a bowl of soapy water nearby to drop them into. Check your plants in the morning and in the evening. The squash bug is normally found underneath the leaf but you will have to be quick as they hide quickly when they are disturbed. Use a butter knife to scrape the eggs off the leaves. Knock them to the floor and they are eaten by beetles. They take 10 days to hatch so make sure you check at least once a week.
  • Use companion planting to help repel the unwanted bugs. Tansy and nasturtium are also popular with squash bugs and will help keep the bugs off your vegetables.
  • In the fall, make sure you burn or compost your old vines so they cannot be used to breed on over winter.
  • Avoid deep levels of mulch around your plants as this is very popular with squash bugs.
  • Keep your vines covered until blossoming begins during the first month of spring. Once pollination is required you can remove the netting. There is only one generation of squash bugs produced per year, and it occurs relatively early. So, if you keep your young plants covered until they require pollination, you should miss the breeding season and subsequent infestation.
  • Use Diatomaceous Earth to rid your plants of squash bugs. This contains no toxins and works very quickly. Dust the Diatomaceous Earth lightly over the affected plants. This works better on the nymphs than on the adults due to their hard shell.
  • Placing boards near the plants makes a great place for the bugs to hide overnight. First thing in the morning they can be easily caught and disposed of.

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