Destructive critters pests of the week

Potato leafhopper and bagworm check

Also construction, landscaping and trees advice         

By John Fulton

[JULY 17, 2006]  With the attack of the Japanese beetles, it is easy to overlook some of the other insect problems that occur annually. Included would be the potato leafhopper. This is the small, wedge-shaped, light-green insect that seems to just fog around security and patio lights. They are not only a nuisance, but they can cause damage to a wide variety of plants.

Potato leafhopper

Potatoes are the first plant that comes to mind when we talk about potato leafhoppers (must be something about the name), but many other plants ranging from beans to trees can be affected. Roses have received some major damage in some plantings. You may be wondering what kind of damage a few little leafhoppers can do, especially since they suck sap from plants and aren't that big in size.

Leafhoppers suck sap and then inject a toxin back into the plant. Along the same lines as humans getting a mosquito bite, it's the extra that's injected back in that causes the injury. Symptoms of leafhopper damage start as yellow "V"-shaped areas on the tips of leaves. These areas turn brown or black and then fall out, leaving a "V"-shaped hole on the tip of the leaf. This is a symptom but not the only injury. Large numbers of leafhoppers can kill potato and other plants.

Controls for leafhoppers are warranted with very low numbers. In alfalfa fields, it is recommended to treat when two leafhoppers are caught in a sweep net in alfalfa over a foot tall. Garden treatment options for potatoes include Sevin, permethrin and rotenone as common insecticide choices available to homeowners. Most trees and shrubs can be treated with Sevin or permethrin.

Bagworm check

Now is the time to check and see if your bagworm treatments were as effective as you wanted them to be. If you haven't sprayed for bagworms yet, you may want to do the plant inspection immediately to see if you have the problem.

No insecticide provides 100 percent control. If you have 500 bagworms on a tree and a product gives 80 percent control, that still leaves 100 bagworms. That's why it is important to check for bagworms, or remaining bagworms.

Bagworm numbers have been highest on evergreens such as arborvitae, juniper and spruce but have also been found on oak, apple and ash this year. If bags are less than one-half-inch long, most insecticides will do a good job. If they are larger, the Bt products will do a better job. Remember with Bt that the actual death of the larvae will take a while, but they do get sick soon after eating the bacteria.

Construction, landscaping and trees

There seems to be an increasing trend to do major landscaping around existing trees. This could be adding raised beds or doing grade work for construction or water control. This is extremely dangerous to the health of many species of trees. Most tree species will not tolerate the addition of even 2 inches of soil around them. The increased soil weight essentially compacts the pore space in the soil and "smothers" the tree, since oxygen is much less available.

Placing any additional soil against the trunk creates an environment that is ideal for some of the rot diseases like crown rot. Very few species will thrive if 4 inches or more of soil is added over the root areas. Trees that will tolerate small to moderate amounts of fill are generally "flood plain trees" that are used to having extra silt dumped on them during flood periods. Some examples would include willows, box elders, sycamores and others you see growing along river systems. Sugar maples, white oaks, lindens and beeches don't really tolerate any additional soil.

Keep this fact in mind when planning landscaping projects in the future. Trying to control the pore space in soil is a fairly complex procedure and probably not worth the extra aggravation and cost.

[John Fulton, unit leader, University of Illinois Extension, Logan County Unit]