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July 24, 2024 - Defoliators Cause Periodic Disturbances

 Watch for signs of these common defoliators in your yard and garden.

“In any given growing season, you might encounter dozens of insects. There are many different insect pests that feed on the plants in our yards, gardens, fields, or forests” says Robert Spencer, horticulturist. “Some of them are subtle about it, sneaking around the fringes or hidden from our view most of the time. Some pests congregate together, having an “in-your-face” smorgasbord with their entire family group.”

Some insects leave obvious signs of their presence, even if you do not see the pest themselves, whereas others nibble away without many outward signs. Some pests are easy to recognize and perhaps easier to control than others.

The most obvious defoliating insects tend to be caterpillars, or the larvae of butterflies and moths. This is a large group of insects, but their common denominator, says Spencer, is that they are “voracious leaf munchers.” As they get larger, the amount that they consume increases. They might consume all or part of the leaf. Some are solitary, hanging out alone, eating their way towards maturity. Others cluster in groups, either in a writhing nest, or just in a large assembly. Caterpillars range in colour, hairiness, striping, etc., with some being showy and others inconspicuous.

“Early signs that you have one of these pests would be the gradual thinning of the canopy of the plant, or perhaps the disappearance of small seedlings,” says Spencer. Individual leaves may be partially or entirely consumed. “You might notice the product of their eating, as they are not house trained, and will leave their frass (a fancy word for poop) lying around.”

Some, such as the Forest Tent Caterpillar, may be first recognized by their distinctive egg clusters/rings around the host tree branches or trunks. Once the larvae emerge, they will be a vibrantly coloured group of caterpillars of varying sizes, rapidly removing the leaves from trees across a large area. They tend to have “nests” or webbed groupings or “home bases” as well. In outbreak years, the caterpillars can be found moving across roadways to new feeding areas, resulting in a messy, slippery wave of larvae.

A common garden defoliator is the Imported Cabbageworm (sometimes referred to as a Cabbage White), which is easily recognized by its distinctive white butterfly adults that flutter around the Brassica species in the garden as mid-summer arrives. They have a few black markings on the wings and do no damage as adults. The larvae are not all that showy, but they are green and feed in and around the various types of heads of this group of vegetables. They eat lots of holes and leave a lot of poop behind.

“Cutworms are chubby plant assassins,” says Spencer, “as you rarely see them on the plants, and the main sign of their presence is the gradual disappearance of the seedlings.” If you do see them, it will only be in the evenings, or if you dig under the soil surface. The adults are moths, but the larvae curl up in a C-shape when disturbed.

There is another group of caterpillar-like larvae that are significant defoliators. They are not true caterpillars, but sawfly larvae can give caterpillars a run for their money when it comes to stripping a plant of its leaves. There are several sawflies that show up regularly and might be familiar. While on the surface, sawfly larvae and caterpillars might not differ appreciably, it can make a big difference when it comes to controlling them.

Spencer suggests that the easiest way to tell the difference between a caterpillar and a sawfly is to count the number of pairs of legs. “If you can spell out SAWFLY on the legs of the critter, you know what you are dealing with.”

Some insects only consume the blade tissues of the leaves, leaving a skeleton behind. Some insects feed within the safety of a rolled leaf, or a group/cluster of rolled leaves. Suddenly seeing the visible area of foliage reduced can be startling.

Leaf miners tunnel between the upper and lower leaf surfaces, chewing out a pocket of emptiness, and filling it with their debris. Some leaf miners chew in a winding or serpentine pattern, whereas others start at one spot and just expand their feeding outward. Over time, the areas where feeding has occurred will fade and turn brown, and leaves will often fall off.

“There is little doubt that you will run across some sort of defoliator in your yard or garden,” says Spencer. Even before you identify the exact name of the culprit, attempt to determine the severity of the pest. In many cases, for most big trees, most of the feeding is cosmetic. In most cases, you observe/recognize and identify problems in one year, and then come up with a management strategy for the next year. For smaller, annual plants, a quicker reaction may be required, but you will have to watch carefully to get ahead of the damage.