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.
This article appears in Jul 21-27, 2005.
