Hot weather has lingered long and lazy into September. We may yearn for the cooler weather of autumn; however, many insects are perfectly happy with heat. Here in September, a flurry of flight may greet plant huggers.
According to Phil Nixon in a recent issue of the University of Illinois Extension's Home, Yard and Garden Pest Newsletter (http://hyg.ipm.illinois.edu/), whiteflies are a common sight in the landscape, feeding on the leaves of many flowers, shrubs and trees. Tomatoes and the weedy velvetleaf, also known as buttonweed, are commonly infested.
As their whitefly name implies, they are 1/16-inch-long insects with white, powdery wings. They sit on leaf undersides and fly short distances when infested foliage is disturbed. They suck plant sap, which can cause leaf distortion.
Generally, late-season whiteflies can be ignored; their feeding is too late to cause serious damage to plant health or even cause obvious aesthetic damage.
In greenhouses, whiteflies can cause serious problems. However, outdoors we have the natural leaf drop and cooler temperatures of autumn working in our favor. Whiteflies are not particularly strong fliers, so a heavy stream of water on the undersides of leaves may be enough to lower their populations and at least make us feel better that we are doing something to curb their conduct. If more management is required, insecticidal soap or neem oil provides some control of whiteflies.
Potato leafhoppers are another minuscule insect that flee with flight when you brush against landscape plants, or their tiny dead bodies often litter indoor light fixtures. Nixon reports these tiny insects and their damage have become obvious during recent weeks. Potato leafhoppers attack oak, maple, red mulberry, red bud, cottonwood, birch, apple, dogwood, hawthorn, wafer ash, euonymus, black locust and cherry.
Red maple is most severely damaged. The expanding leaves at branch tips are curled and stunted, and they are mottled with light green, red and brown. Leaf edges and entire leaves may turn brown or black. Stem growth is greatly reduced.
Overall, the damage looks similar to the 2,4-D herbicide injury, and potato leafhopper damage may be frequently misdiagnosed as herbicide injury. Leafhopper damage this fall is heaviest at the top of the tree rather than on side branches. On other host species, leaves may be misshapen, have brown areas, show early fall color or have stippling (light dots).
Potato leafhopper adults are wedge-shaped, green and about 1/8 inch long. They fly readily from foliage when approached and are very migratory, making it difficult to find the insects on damaged foliage. They are strongly attracted to lights at night and are small enough to go through the mesh of window screening.
Leafhoppers are the annoying little green bugs that fly indoors around the newspaper or book you are trying to read during summer evenings.
This late in the growing season, treatment for leafhoppers is probably not warranted. These insects start feeding in May in Illinois, and treatment at that time to prevent leaf damage and reduced growth through the growing season may be necessary.
So the morals of the story: Insects often travel in herds; insects compensate for their tininess by being numerous; don't breathe too deeply when hugging landscape plants or numerous tiny insects may go up your nose; and check the calendar when deciding if insect control is warranted.
Upcoming Extension event
Join Master Naturalists for Discover Illinois — Exploring Nature from 6:30 to 8 p.m. Sept. 23 at the UI Extension auditorium, 801 N. Country Fair Drive, C. It will be presented by Susan Post, author and retired field biologist with the Illinois Natural History Survey, who along with her husband, Michael Jeffords, has been hiking, exploring and photographing Illinois for more than 30 years.
For more information, call 333-7672 or visit http://web.extension.illinois.edu/cfiv/.
Lend a hand later this month
Volunteer for National Public Lands Day on Sept. 28. For more information, visit http://www.publiclandsday.org.
Sandra Mason is unit educator, horticulture and environment, for the UI Extension, Champaign County. Contact her with questions or comments at 801 N. Country Fair Drive, Champaign, IL 61821, call 333-7672, email firstname.lastname@example.org or fax 333-7683.