Up until last week, at least one of three calls to local master gardeners for help concerned those pesky Japanese beetles.
But now there’s new trouble in Lincoln Land, and the question of the week is: “What is eating my Euonymus alata compacta?” The experts all agree on what’s chewing on your burning bush plant: It’s two-spotted spider mites.
Here’s the skinny on this garden pest from local entomology extension specialist Raymond Cloyd:
Why so many? The two-spotted spider mite, Tetranychus urticae, tends to multiply rapidly under hot, dry conditions — such as the ones we have experienced this past month. When conditions are moist and rainfall is sufficient, these mites are generally not a problem because naturally occurring fungi keep them in check. (Under conditions of low rainfall, populations of natural fungi decline, allowing mite populations to increase.) The two-spotted spider mite is mainly active from late spring through early fall.
Female mites, which don’t have to mate to reproduce (this doesn’t sound like much fun), may live as long as four weeks and lay as many as 300 eggs.
What’s on the menu? Two-spotted spider mites feed on a wide diversity of trees and shrubs, including ash, azalea, black locust, elm, burning bush, maple, oak, poplar, redbud, and rose. They also feed on such herbaceous annuals and perennials as marigold, pansy, columbine, butterfly bush, clematis, daylily, delphinium, phlox, rudbeckia, salvia, Shasta daisy, and verbena.
The mites attack the undersides of leaves. Affected leaves are stippled with small silvery-gray or yellowish speckles. Plant leaves heavily infested with mites will appear bronzed, turn brown, and eventually fall off.
Telling one mite from another. Adult two-spotted spider mites are oval and approximately 1/50 inch long (you’ll need a hand lens to see the little guys — or sneak a peek at the U of I Extension IPM Web site, www.ipm.uiuc.edu/fruits/insects/strawberry_mites/index.html).
Two-spotted spider mites vary in color from greenish yellow to reddish orange, with two lateral dark spots. Adults and nymphs are found on all plant parts but are more numerous on older leaves. The mites produce a fine silk, which is sometimes observed between leaves and between the petiole and stem. This webbing protects mite populations from their natural predators. A heavy rainfall usually washes this webbing away.
Getting rid of them. Management of two-spotted spider mites involves maintaining plant health, proper sanitation, and the use of appropriate pest-control materials (miticides). Keep an eye out for two-spotted spider mites by knocking them off plant parts such as leaves or branches onto a white sheet of paper, where they may be observed more easily. Plant-feeding spider mites produce a green streak when crushed; predatory mites produce a red streak.
One effective and cost-efficient way of dealing with two-spotted spider mites is to apply a hard spray of water, which dislodges mites in all stages of life, including eggs, from plants. Removing plant debris and weeds eliminates overwintering sites. In addition, many weeds, especially broadleaves, are hosts for two-spotted spider mites.
Pest-control materials recommended for two-spotted spider mites outdoors include bifenthrin, dicofol, fenbutatin-oxide, insecticidal soap, and horticultural (summer) oil. Be sure to make applications before mite populations are high and aesthetic injury becomes noticeable. Concentrate spray on underside of the foliage. Many pest-control materials recommended for two-spotted spider mites are harmful to beneficial insects and mites that naturally feed on them, potentially leading to continual use of these materials once applications are initiated.
Evening in the garden
Members of the public are invited to tour the Master Gardener Demonstration Garden on Tuesday, July 26, where they may inspect the new “herbs for tea” garden, new landscape designs, and other new features. The free tours begin at 6:30 p.m. in front of University of Illinois Extension Building at the fairgrounds.
Master gardeners of the U of I Extension Sangamon-Menard Unit will be present to answer questions on the wide variety of annuals, herbs, and perennials in the 5,000-square-foot garden.
For more information, call 217-782-4617.
Know your enemy
To manage weeds, you need to be able to identify them.
Michelle Wiesbrook, a weed-science extension specialist from Urbana, will discuss the key characteristics of 22 common lawn-and-garden weed species at a seminar next week.
“Lawn & Garden Weeds” is offered at 1 p.m. Tuesday, July 26, and repeated at 7 p.m. Thursday, July 28. Programs will be held at U of I Extension Building at the fairgrounds. For information and to reserve a seat (there’s a $2 charge), call 217-782-4617.