WICHE: Summer insects suck and chew

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By Jeneen Wiche

The insect world has countless sucking and chewing pests.

One of the most difficult questions to answer, and I get asked it often, is “what’s eating my plant?”

It could be a chewing beetle, or caterpillar; or it could be a sucking spider mite, bug or aphid, among many, many others. Our early heat wave this summer added an additional component to the problem…many insects love this sort of disagreeable weather and can multiple more rapidly as a result.

There are a couple of indicators of the type of pest problem you may have. Dull or mottled looking foliage suggest some sort of sucking insect. Holes suggest a chewer, no doubt.

But not all holes are from insect damage. Some bacterial and fungal diseases can cause perfect holes to drop out of foliage.

Shot hole disease, often seen in ornamental cherries, shows itself after the spots on the leaves, caused by a fungus, pop out in the shape of a near-perfect little circle. It tricks many people into thinking they have an insect problem!

The most common sucking insects for our landscape plants include aphids and spider mites, and they like a wide range of plant material.

When the weather turns hot and dry, mites become very active on evergreens like arborvitae, hemlock, juniper and spruce. The foliage changes to a dull gray or yellow color as the mites feed on the sap of the plant.

With heavy infestations of spider mite, especially during periods of drought, your evergreens could see some serious decline in one season.

The dark green, to black spider mites are difficult to spot because they are so tiny.

Look for a mass of fine webbing on the needles or leaves of your plants then you can confirm their presence by tapping a limb over a white piece of paper.

If you have mites you will see tiny black specks moving on the white piece of paper.

There are various methods used to control mites. The infestation around the webbing can be broken up by hosing down the plant. This will disperse the mites lessening the adverse effects of their sucking.

There are insecticidal soaps, horticultural oils and chemical controls that are labeled for spider mites but this is really only necessary when large numbers are present. Horticultural oils would be my recommendation in this case.

Aphids suck the vital juices from plants, too, and they have the amazing ability to give live birth to babies after only about a couple of weeks of being born themselves.

They love hot, dry weather, too, and can triple their populations when the weather is right in a matter of a couple of weeks.

Aphids come in a rainbow of colors: green, white, red and black. I have controlled infestations by simply squishing them, but this is not always practical when you have thousands!

Again, insecticidal soaps and horticultural oils will control these soft-bodied insects.

Beetles, bugs and caterpillars are often the culprits if you see chewing on your plants, and they are a little more difficult to control.

Beetles and many plant bugs have hard bodies so they will not respond to pesticides as well as soft-bodied insects. Treatment usually ends up being something that the leaf-eater will ingest, so this means we apply the control to the plant’s foliage, and the insect then eats the leaf and, hopefully, dies.

The arsenal for controlling chewing insects continues to grow and the good news is that many biological controls are now available.

Biological controls are quite effective against caterpillars but they must be ingested by the leaf-eater. Some products act as an appetite suppressant so the pest stops eating and starves to death.

The key to using many of the biological controls, however, is early detection of the problem because they work better if the caterpillars are still small.

Bacillus Thuringiensis (BT Kurstaki strain) and Spinosad (a naturally occurring soil bacterium) are two effective biological controls that are labeled for use in the home garden. And, when you can hand picking pests and dropping them into a bucket may be the best solution after all.