I love to grow squash, but it seems like every year the insects get them. How can I stop this from happening? SB

There are two main insects that are problematic for squash plants: squash bugs and the squash vine borer.

Squash Bugs

Adult squash bugs overwinter in plant debris near where you grow your squash. As the weather warms, they make their way to your squash plants where they feed and mate. Their eggs are laid on the underside of leaves in early June. So, late May through June are good times to inspect your squash plants on a weekly basis. Since they lay their eggs on the underside of leaves, you will need to turn the leaves over to look for the eggs. These eggs are laid in groups and pretty easy to spot. They are oval, kind of shiny, and copper in color. If you find these eggs during your inspection, just remove that leaf with the eggs and throw it away.

The eggs hatch in about a week to reveal small, greenish nymphs that are quite hungry. They go through several growth stages (instars) until becoming an adult. It’s not unusual to see adults and green nymphs in the same place during large infestations. A second generation follows this first one in the fall with adults then moving on to overwinter in plant debris. Mild winters enable the squash bugs to survive to the next year. With the deep-freeze we experienced earlier this year, hopefully their population got beaten down a bit, but only time will tell.

Both the nymphs and adults feed with what we call piercing-sucking mouth parts. These piercing/sucking mouth parts puncture the leaves, enabling the squash bug to literally suck the life out of the plant. As they continue to pierce and suck, they damage the plant tissue making it unable to move water. Ultimately, this causes the entire plant to collapse and die.

Control of these insects can be challenging. Spinosad can be effective before the squash bugs mature into adults while pyrethrins can work on the adult population (follow instruction on the insecticide). Early control is key since this is the best way to limit squash bug populations quickly.

Another strategy involves placing a 2x4 on the ground close to your squash plants. Squash bugs tend to congregate at night and seem to like to get together under these boards. After placing the board, just go out to your garden first thing in the morning and check under the board. If you find squash bugs, “squashing” them can be quite satisfying.

Squash Vine Borers

The adult squash vine borer is actually a moth with black and orange coloring (Go Pokes). Adult squash vine borers begin to lay their eggs about the time squash plants start to flower. Each female can lay up to 200 eggs. These eggs hatch in about 7 to 10 days. So, you do have a bit of a window there for visual inspections to be effective. Inspection is challenging though, because their eggs are laid on the stalk at the soil line. Finding and destroying the eggs is your first line of defense.

After the eggs hatch, they immediately tunnel inside the plant and begin eating. This feeding can last 30 days, although your squash plant probably won’t last that long. After the larvae mature, they exit the plant and burrow into the soil to pupate and overwinter.

Once the squash vine borer larvae begin to devour the inside of the squash plant stems, there’s not a whole lot you can do. If you catch it early, you can slice open the stem and physically remove the larvae. After doing this, bury the damaged portion under the soil and hope it begins to root. Personally, I have not had success with this method. You can also try injecting bT (bacillus thuringiensis) into the stem if you see damage since this organic pesticide controls caterpillars, but while you may kill the larvae, damage is oftentimes too severe for the plant to recover.

The primary way to tell if your plant damage is the result of squash vine borers is to look at the larger stems. Stems that are host to the larvae are yellowish, kind of squishy, and you will likely see a yellow-green sawdust looking substance. This is the frass (poop) of the squash vine borer larvae.

To defend against the squash vine borer, you can till the garden soil in the fall and again in the spring before planting. Since the borers overwinter in the soil beneath your plant, this will bring them to the surface where exposure to the elements or perhaps hungry birds will help diminish the population. It’s also a good idea to rotate your corps so that you don’t plant squash right above the overwintering borers.

Insecticides such as pyrethrin or spinosad are organic pesticides that can be effective, but timing is critical since you must spray while the adults are active and before the larvae tunnel into the stem (follow instruction on the insecticide). Once they are inside the stem, your battle is almost always lost. Maybe it’s time to think about growing cucumbers instead.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.

Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org