Watch for plant damage from hungry insects

Now that summer is finally here, the insect population is having a daily picnic — on your plants.

If you, like most gardeners, are observing your plants on a daily basis, you will notice almost immediately when insect damage begins. The location and type of damage will provide clues to identifying the pest munching away on your prized roses or your tree fruits or your marigolds.

Check the leaves for signs of chewing/rasping. If the entire leaf blade is consumed and only the midvein remains, there may be caterpillars or canker worms. If chunks are missing out of the leaf margins, the culprit might be black vine weevils or leaf cutter bees.

Small, randomly scattered holes in the leaf could be grasshoppers or beetles.

Damaged leaf surfaces can be caused by slugs, beetle larvae or thrips. Thrips also often infest unopened flower buds, especially on roses. If leaves are curled or rolled into tubes, the leafroller may be to blame.

Sucking insects such as aphids, leafhoppers, spider mites and plant bugs cause damage by injecting toxic substances into the leaves. Symptoms range from simple stippling (dots) or chlorotic (yellowing) patterns to extensive disruption of the entire plant, resulting in leaf and stem distortion, off-color foliage, reduced growth, or dieback of twigs or stems.

Spider mites can cause leaf stippling or bronzing. Foliage may appear dirty because of the presence of small, fine webbing on the undersides of leaves.

Slugs and snails feed on low-growing foliage and fruit, causing destruction of soft tissue. A sure sign of slugs or snails is a slime trail on the foliage or surrounding soil.

There are any number of insects that attack our vegetable gardens, from root maggots and nematodes that feed on the roots of the plants and cutworms that chew on the seedling stems, to aphids, mites, leafminers, and various beetles and worms.

The larvae (wormlike creatures that hatch from the eggs laid by the adult female) of many insects can be more damaging to your plants than the adults. Butterflies, moths, beetles, and flies are examples of larvae that are ravenously destructive until they become a pupa (cocoon). Once the adults emerge, they cause little harm to our gardens.

So what to do about these hungry critters that seem bent on total destruction of your garden?

First, be absolutely certain you know what insect is causing the damage. If you are uncertain, bring a sample of the plant damage (and a few healthy leaves for comparison) to the Washington State university/Spokane County Master Gardener Plant Clinic (222 N. Havana St., just south of the fairgrounds, open Monday through Thursday from 9 a.m. to 3 p.m. and Friday from 9 a.m. to 1 p.m.) for diagnosis and treatment advice.

In general, cultural practices such as planting pest-resistant crops and maintaining good plant health will provide adequate control. Aphids, thrips, and many other insects can simply be washed off the plants with a strong stream of water from a hose.

You can also try spraying the plant with insecticidal soap. Don’t forget the undersides of the leaves.

In vegetable gardens, row covers can help protect plants from leafminers, beetles, thrips and various maggots. Plant collars inserted in the soil around the plant can reduce the threat of cutworms.

Often just picking off the offending caterpillar or worm will eliminate the problem.

Some insects have natural enemies that will control the infestation, or a change in the weather will reduce the population without your intervention. Only you can determine whether the damage is severe enough to warrant more intense treatment.

Be cautious in the use of pesticides. Many times these products can kill beneficial insects as well as problem ones. If you do decide to use a pesticide, make sure you choose the right one for the problem.

Read the label carefully and follow the directions. More is not better.

This week in the garden

If you don’t have your weed problem under control by now, get busy! Weeds compete with desired plants for nutrients and precious water. They will also be setting seed soon.

As annual flower blooms fade, remove them to encourage new flower development.

Fertilize your lawn now and again in early September.

Water gardens and lawns in the early morning to minimize water loss due to evaporation. Deep-water trees and shrubs every couple of weeks during the hot weather.