ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
The lilac borer (also known as the ash borer), Podosesia syringae, can cause considerable damage to lilac and ash. Perhaps this is one reason lilacs are not grown more widely in North Carolina. The larval borers of this clearwing moth 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 to protect 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.
Older literature about moth emergence period was confusing. Pheromone trials showed that there is a second species of clearwing moth borer which emerges in late August/September. This one is called the banded ash clearwing, Podesia aureocinta, determined by a narrow gold band around the fourth abdominal segment and the time it emerges. The banded ash clearwing is thought to also infest lilac. Protective insecticide sprays would need to be started in mid August. If a plant had both borers, it might mean an entire season of protective sprays.
As field corn dries and become less suitable for egg laying, summer
generations of yellowish-brown European corn borer moths oviposit
on more than 200 different plants including chrysanthemums, asters,
cosmos, dahlia, gladioli, hollyhocks, roses, zinnia and some
vegetables as well. There may be three generations of borers per
year. The moths first appear in late spring. Females lay up to
400 eggs in flat masses on the underside of host plant leaves. The
eggs resemble tiny fish scales in shape and arrangement. The
borers hatch and feed on the surface of leaves for a few days. As
the borers mature, they bore into the host plant stalk to feed.
The borers push frass mixed with silk out of the entrance hole.
European corn borer caterpillars are cannibalistic. This explains
why only one or two borers are found in a pot of mums even though
the moth laid dozens of eggs. This pest overwinters in the stalk
as mature larvae, so destroying the stalks of corn, dahlia, mums
and weeds in the area will help to suppress next season's
population. They pupate inside the stalk. The best recommendation
of a pesticide for commercial growers is a pyrethroid such as
Talstar, Mavrik, or Tempo 2 sprayed every month or so. After the
borers are in the stalk it is essentially too late, although a
desperation spray of Dursban (DuraGuard) could be tried. Culling
and destroying infested stalks in the winter may be helpful. There
is additional information on the biology of the European corn borer
is Publication AG-136, Insects and Related Pests of Flowers and
Foliage Plants. A copy of this North Carolina Cooperative
Extension Service publication should be available in county
Extension centers in North Carolina.
Web page last updated on July 20, 1998 by Stephen J. Toth, Jr..
