Potato leafhoppers and lawn rust

By John Fulton

[August 04, 2009]  Insect of the week honors go to the rather inconspicuous potato leafhopper. This is the small wedge-shaped, light green insect that seems to just fog around security and patio lights. They are also small enough to come in through screens after dark. They are not only a nuisance, but they can cause damage to a wide variety of plants.

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. 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, bifenthrin, permethrin and rotenone as common insecticide choices available to homeowners. Most trees and shrubs can be treated with Sevin, permethrin or bifenthrin.

Rust

This is basically a reprint from a few weeks ago -- predicting rust in lawns is one thing, but having it full-blown is something different. The drier weather we have been experiencing has made rust an all-out problem for many homeowners.

As grass growth slows, rust will be one of the lawn fungi we are dealing with. Rust appears as an orange or yellowish-orange powder (spores) on grass leaf blades, especially when the weather is dry in late summer to early fall. Rust typically develops on lawns growing very slowly. Overall, the turf may assume a yellow, red or brown appearance. Close examination will reveal the pustules, which easily rub off on your hand. Rust spores can easily be tracked into homes.

Low fertility (in particular nitrogen) and low water availability slow down turf growth, allowing rust to develop. Seasons with excess rain may have rust outbreaks due to loss of available nitrogen. Light, frequent rainfall and cool nights with heavy dew add to the ideal conditions for rust to develop. Warm, cloudy, humid weather followed by hot, sunny weather also favors rust development on lawns. Kentucky bluegrass, perennial ryegrass and tall fescue are all affected, depending on cultivars. Rust spreads through air, water, shoes, equipment and sod. Rust may weaken turfgrasses and make them more susceptible to other problems.

Control rust through sound turf management. Begin by choosing a quality blend of turfgrass seed. Resistance to rust can vary according to the race of the disease present. Maintain lawns through sound watering, mowing and fertilizing. If you are watering, water early in the day so the grass dries quickly. Manage problem thatch. Increase vigor with an early fall nitrogen application, but don't overdo it. Check soil phosphorus and potassium levels through soil testing. Also assure good airflow over the site and good light penetration by pruning trees and shrubs in the area near the lawn.

When rust occurs at this time, improved growth conditions of early fall often get lawns growing more vigorously and the rust fades away. Early September is a key time for fertilization. If conditions are dry, irrigation is also needed to increase the growth rate of the lawn.

Fungicides are rarely suggested on home lawns for rust control. Focus on the listed cultural practices described above.

[By JOHN FULTON, University of Illinois Extension, Logan County]