Potato leafhoppers, lawn rust and weedy grasses

By John Fulton

[July  13, 2011]  Potato leafhoppers -- 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.

Leafhoppers suck sap and then inject a toxin into the plant. It's the extra that's injected that causes the injury -- along the same lines as humans getting a mosquito bite. 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 potatoes 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

The weather we have been experiencing has made rust in lawns a problem for many homeowners again. 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 in late summer to early fall when the weather is dry. 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 (nitrogen in particular) 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. Cool nights with heavy dew and light, frequent rainfall 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 for rust control on home lawns. Focus on the listed cultural practices described above.

Water grass

"Water grass" is one of those names that mean different things to different people. In our area, the main two weeds called water grass are crabgrass and yellow nutsedge.

Nutsedge isn't even a grass, hence the name. It is easily identified by its triangular-shaped stem. Control in lawns is usually accomplished with bentazon (Basagran) or halosulfuron, and neither is something you usually find in the local garden shops. Roundup can help suppress it, but isn't very effective on the mature plants -- and it will also kill your grass. Usually you need at least two applications 10 days or so apart at the minimum.

The other main weedy grass called water grass is crabgrass, and at this point it will probably just need to run its course for the season. Next year, a preventive treatment could be applied early and repeated six to eight weeks later.

[By JOHN FULTON, University of Illinois Extension]