ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable to North Carolina
and may not apply in other areas.
Fall webworms are related to woollybear caterpillars and tiger
moths. The caterpillars have dense hair. Although they occur
all summer, they are called fall webworms because their webs
accumulate during the growing season and by fall the webs are
sometimes quite conspicuous. Infested trees may be completely
webbed. Because fall webworm damage accrues over the summer,
fall webworms usually cause little long-term health damage to
trees, unless the trees are completely defoliated year after year.
At any one location, the populations of fall webworms wax and wane
so that they are conspicuous and damaging for a year or two, then
the populations seem to disappear. They overwinter as pupae in
cocoons in the litter. White moths emerge to mate and lay 350 to
900 eggs on the lower leaf surface. The hairy caterpillars spin
the webs as they feed. There are two generations of caterpillars
each year. Bacillus thuringiensis, bendiocarb, Dursban, diazinon,
Orthene, Dibrom, Imidan, sumithion and Talstar are specifically
labeled for fall webworm control. In the county extension centers
in North Carolina is Ornamentals and Turf Insect Note
No. 46 which has additional information on the biology and control of fall webworms.
Lilac borers can cause considerable damage to lilac. Perhaps this
is one reason lilacs are not more widely grown in North Carolina.
The borers may riddle the stems to the point that they break off.
Newly hatched lilac borers make a blotch mine just under the bark.
As they grow, they bore into the wood and the moths finally emerge
the following spring from a neat hole. Lilac borers are also
called ash borers and they infest Marshall seedless ash and other
landscape varieties with a vengeance. The lilac or ash borer is a
native species that occurs over much of the eastern United States.
It has one generation per year. The peak emergence of the adult
moths is May in North Carolina. Ash borers are a perennial problem
because forest and landscape ash trees remain a source of the
insects. Dursban can be used for protecting lilacs from lilac
borers. It should be applied around the first and third weeks of
May. The formulation of Dursban suitable for home use can be
purchased in local garden centers.
White Peach Scales. White peach scale insects are pests of peaches and related trees as well as lilac, ligustrum, walnut and other woody plants. White peach scales can be quite damaging and infested plants may be stunted and die back or completely killed. Because the white peach scale is an armored scale insect, it is susceptible to the horticultural oils. These oils can be used at a growing season rate from bud break until late December or can be used at a dormant spray rate during the winter to reduce the overwintering population. John Meyer of the Department of Entomology at North Carolina State University conducted experiments on the control of white peach scales a few years ago and found that oils would suppress white peach scales. It is probably best to apply the oil, wait two or three weeks, and apply it again. The crawlers of white peach scale can be present in low numbers throughout the year, but there are distinct peaks of crawler emergence in early May, mid July, and early September. Another strategy for control of these insects is to wait until early May and apply Dursban; some formulations of Dursban are specifically labeled for white peach scales. White peach scales have two very effective natural parasites, Encarsia berlesi and Aphytis proclia. However, large white peach scale populations and shrubs or trees with dieback indicate that the parasites are not effectively controlling the pest. Horticultural oils probably have less impact on the parasites than Dursban.
Euonymus Scales. Euonymus scales are common and sometimes very damaging pests of euonymus and a few other ornamental plants. The males have snowy white armor and are sometimes quite conspicuous against the leaves. Females have gray, oyster-shaped armor and are less conspicuous. Females and males can be found on stems as well as leaves. Ornamentals and Turf Insect Note No. 15 provides information on the euonymus scale and its control. Horticultural oil or Cygon used for euonymus scale suppression should also control spider mites and other pests of euonymus.
Gloomy Scales. Gloomy scales make the bark of infested maples
rough, dark and unsightly. They also cause twig dieback. Gloomy
scales are armored scales. They overwinter as mated females and
the young scales are produced from May to the middle of August.
Gloomy scales are susceptible to horticultural oils, but infested
trees may be large and difficult to spray. Because the scales
build up in layers, it may be very difficult to obtain good control
by spraying. It is probably better to spend energy getting an
infested tree into good growing condition than to waste energy
spraying with improper equipment. First, submit a soil sample to
the North Carolina Department of Agriculture Soils Laboratory. If
the pH or nutrients are out of balance, the soil should be
amended. Second, if there is another period of prolonged drought
stress this summer, the tree should be irrigated. Third, apply
Roundup on the grass under the tree and mulch the soil to conserve
soil moisture and keep the roots cool. Every effort should be made
to enhance the vitality of the trees. Trees under stress have more
simple sugars (rather than starches) and more free amino acids
(rather than more complex proteins) in the sap. Thus, stressed
trees are more nutritious to the scales than healthy trees. The
bark of an unsprayed tree is often like a microscopic zoo with
all sorts of predaceous mites, predaceous insects, parasitic fungi,
parasitic insects and other organisms as well as the scales. A
tree in top growing condition should be less susceptible to the
scales and the scales will not reproduce as prolifically. As a
consequence, the parasites and predators may control the scales
almost completely. In the county extension centers is
Ornamentals and Turf Insect Note No. 60 that provides additional information
on the biology and control of gloomy scales.
Web page last updated on 15 July 1996 by Stephen J. Toth, Jr..
