Fungus and squash bugs wreak havoc on gardens

I am growing squash plants for the first time in my garden. Suddenly, leaves look brown and yellow and are just collapsing. I am finding some insects that look like brown stink bugs under the leaves. Stink bugs are good, so why am I having problems?

The phrase “looks like” is not the same as “is.” Looks can be deceiving because many insects share body shapes. You are actually looking at a squash bug.

Leaf damage and hordes of galloping triangular insects on squash leaves mean squash bugs. They share a similar body shape with stink bugs, western conifer seed bugs, assassin bugs and leaf-footed pine seed bugs. This insect can be classified as a sucker and that’s not a moral judgment. It indicates how they feed. All bugs are sucking insects.

The squash bugs are sucking chlorophyll-y goodness out of the bottom of your squash leaves. Leaves turn yellow, brown and then gray and dry up. Flip over leaves and you will find small, immature gray squash bugs racing around and clusters of orange-brown eggs nestled next to leaf veins. The adults are brown and bodies are shaped like an equilateral triangle with the base at the head end. The head protrudes beyond the triangular shape.

If you don’t put an end to their reign of terror, there will be no leaves and the squash crop is abruptly halted. If you are looking at control using no pesticides, consider organic greenhouse production techniques to hunt for eggs each day and destroy them. Lay boards or newspapers under plants and collect hiding adults the next morning. Remove debris from around the garden to cut down on places for insects to overwinter.

If you have an organic garden, you can spray the young squash bugs with insecticidal soap or a permethrin product. For others, sevin liquid, bifenthrin with a brand name such as Talstar or a pyrethroid called esfenvalerate will be effective. Squash bugs can also go after pumpkins and cucumbers so check when treating the squash. Keep plants watered and fertilized to help them recover from their squash bug beating.

My two crabapple trees look horrid. Most of the leaves are yellow with brown spots and leaves are falling off daily. Right now, I have less than half of the leaves remaining on the trees. What do I do? I have looked every day for some kind of bug or worm and there aren’t any.

There aren’t any insects because a fungus is causing the problems. It’s called apple scab and will affect both apples and crabapples. Left untreated for a few years, with this kind of early defoliation, the trees may die. Good news is that it is controllable. Bad news is it can’t be controlled this year.

Once a fungus enters a leaf, it cannot be extracted. The fungus entered the leaves just as they were unrolling and growing early in the spring. When we use fungicides, the products protect but don’t cure. Think of fungicides as an invisible raincoat to keep the bad stuff out. So, this year, keep the trees watered if it is dry and lightly fertilized.

Make plans for next spring and your “Repellency Project.” The fungicide you need is called chlorothalonil. You could also use captan. If you are eating the fruit, use captan or an all-purpose orchard spray containing captan. Only use chlorothalonil if you are not eating the fruit.

Begin spraying in the spring when the leaf buds begin to show green. Spray at intervals of seven to ten days for five to eight times. Apple scab needs mild, wet or humid weather to be active. This fall, clean up and destroy leaves. It will lessen the amount of scab around next year.

Contact Gretchen Voyle, MSU Extension-Livingston County Horticulture Educator, at (517) 546-3950.

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