Tips for controlling a stink bug or squash bug infestation

By Bonnie Orr
WSU Chelan/Douglas County Master Gardener

squash bug eggs on underside of leaf.
Squash bugs typically lay their eggs on the underside of leaves, next to the veins. – Wikimedia Commons
Brown marmorated stink bug on a leaf.
The brown marmorated stink bug is not picky when it comes to eating. It will feed on most fruits and vegetables, but is partial to tomatoes, causing damage, as well as grief for the home gardener. – Wikimedia Commons
Bonnie Orr
Bonnie Orr – WSU Extension Chelan/Douglas County Master Gardener – photo by Don Seabrook, Wenatchee World

Nothing is more disappointing than going to the garden and seeing that your winter squash plant has wilted and is mostly dead. Or even worse, the first eagerly anticipated ripe tomato has a hard leathery texture and is punctured with little holes. Two perpetrators, in particular, give such a brazen insult to enthusiastic gardeners.

The insects that cause the plant damage are common garden pests — stink bugs (Halomorpha halys) and squash bugs (Anasa tristis). Often the Master Gardeners hear the wails of disappointment after the insects have created their damage. It might not be possible to eliminate the pests, but it is possible to limit their damage.

The method to control these insects is diligence and a bucket of soapy water. (Chemicals are also possible, but chemicals kill beneficial insects that prey on destructive insects. Birds, spiders, and parasitic wasps prey on these pests.) Stink bugs and squash bugs can fly from plant to plant and run very fast when you try to catch them. They drop to the ground and hide in debris or mulch.

First, let’s consider the squash bug. This adult insect is brown, arrow-shaped and flattish. It only attacks Cucurbit family plants: squash, cucumber, and sometimes melons. They overwinter in debris and weeds. They suck the juices of the plant and cause the vines to die. You do not want to see the adults. You want to kill the eggs before they develop and become adults.

Squash bugs overwinter as adults. They spend the winter in garden debris or old wood, weeds and sticks piles. They appear in mid-June. This is about when you’ll want to plant your various cucurbits. Ask yourself: Do you need to have the first zucchini on the block? If you don’t, then squash bugs can sometimes be avoided if you put off planting the squash or zucchini for a few weeks until late June. The first hatched squash bugs will not find anything to eat in your garden.

Squash bugs begin to lay eggs on the plants when the plants start to extend their vines. This is when diligence is required. The eggs are oval-shaped and shiny brown. They are usually laid on the underside of the leaves next to the veins.

Stink bugs are greenish and flattish, and also overwinter as adults. The stink bug has a shield-shaped body about half an inch long. It emits an offensive odor when you handle them.

Stink bugs, especially the brown marmorated stink bug, feed on nearly any fruit and vegetable. Their favorite food, it seems, is tomatoes. The stink bug is a chameleon and changes color to blend into whatever it is sucking on. I even had one that was purple as it was feeding on my blueberries! They were reddish-brown when they fed on raspberries, and they left an off taste on the fruit. But usually, they are green or light brown. They feed with a piercing, sucking mouthpart that causes the whitish-yellow corky spots underneath the fruit’s skin.

The barrel-shaped eggs are greenish-light brown and are laid on the underside of the leaves right between where two veins meet. They begin to lay eggs when tomatoes are 1 inch in diameter.

For both of these pests, the goal is to eliminate the first eggs. Every day or so, put on gloves, turn over leaves, and squish both eggs and young insects or nymphs. You want to do this so that an adult population does not develop.

Not diligent enough? On a warm afternoon, fill a bucket with soapy water with a dash of vegetable oil. Then spray the plant thoroughly under the leaves and over the entire plant. Wait for a few minutes. To dry off, the insects will climb to the top of the tomato plant or the top of the squash leaves. Pick off the insects and throw them into the soapy water. Scoop out the dead ones and throw them in the trash. The same water can be reused. Repeat daily until the population is under control.

Have a successful gardening season.