September often brings two problems into the landscape - powdery mildew on crape
myrtles and yellow-jackets or hornets swarming - says Bill Dimock, extension agent in
Newport News.
POWDERY MILDEW
The leaves on the crape myrtle begin to fade slightly and the edges may begin to curl
inward. If you look closely at these leaves, you'll see a covering of a powdery substance.
This is mildew fungus, which also attacks and feeds on other related plants. It can be
severe on plants that grow in the shade or on hedges.
The disease is a parasite that looks superficial but penetrates the epidermal cells of
the plant and diverts food and water away from the plant and sends it to the fungus. The
disease usually subsides during the hot summer weather but returns in the fall.
Crape myrtles - often called the ``tree of 100 days'' because of its long flowering
period - should be planted in full sun for the best blooms; the sun also helps prevent
mildew from developing because the fungus prefers moist, shady spots. You can also
minimize mildew on the foliage with February prunings that eliminate crossing and rubbing
branches so air can penetrate the interior of the plant during its growing and blooming
seasons.
The Tuscarora crape myrtle is considered to be one of the best disease-resistant
varieties. It has watermelon red blooms, cinnamon-colored exfoliating bark and an
attractive vase-shaped growth habit that reaches about 25 feet high.
POWDERY MILDEW
AT A GLANCE
NAME: Powdery mildew or Erysiphe lagerstroemiae
CHARACTERISTICS: Grayish, white powder.
PARTS ATTACKED: Infection on young shoots causes stunting and floral abortion. Diseased
leaves and buds usually drop off within a few weeks but the tips of diseased shoots often
outgrow the infection.
DAMAGE: Symptoms of damage include dwarfing, distortion, chlorosis or yellowing of
leaves, premature leaf drop, browning of leaves, abnormal growth rate and poor flowering.
CONTROL: A fungicide recommended by your local garden center or the fungicide called
benomyl, sold under the brand name of Benlate. Benomyl should be applied until it runs off
the leaves and make a second application in 10 to 14 days, says Bill Dimock, extension
agent in Newport News. These two sprays should be sufficient. Always read the label and
follow directions when using any chemical. Many fungal diseases can be controlled by
proper yard care; for instance, remove and destroy infected leaves and prune plant so air
and light get into the interior foliage so mildew has trouble growing there. Safer also
makes a fungicidal spray-type soap made from sulfur in a soap base; apply according to
directions.
YELLOW-JACKETS AND HORNETS
Late summer sends yellow-jackets and hornets scavenging for food in garbage cans and at
picnics because their normal food supply - caterpillars, spiders and other insects - is
dwindling. The hive still has lots of baby wasps that are hungry, so the workers are
searching high and low for food.
They can become quite testy, says Dimock.
Their nest, which looks like a big paper envelope, because they chew wood fibers and
mix them with their saliva to form paper-like hives, isn't perennial. All this frenzy of
activity generally stops with the first killing frost. Yellow-jackets are usually ground
nesters; hornets generally build their nest in the hollows of decayed trees.
Swatting and shooing away the pests tends to irritate yellow-jackets and that's when
they sting, says Dimock.
