The orangestriped oakworm is sometimes very abundant on oaks in late August and September. In NC, willow oak and pin oak tend to be their preferred hosts. They occasionally feed on other hardwoods as well. The moths emerge in June and July and deposit their eggs in clusters of several hundred on the underside of oak leaves. The eggs hatch in about a week or so. The tiny, green-colored caterpillars begin to feed together consuming leaves except for the midrib. Gradually small greenish caterpillars grow into larger black caterpillars with yellow or orange stripes running lengthwise along their bodies. These caterpillars have a prominent pair of spines or slender horns sticking up behind the head.
Defoliation is probably not good for any tree, but this late season leaf removal
is not likely to kill an average tree. Some oaks have been severely defoliated
for many years in a row without obvious affect.
Young caterpillars feed in groups, whereas older caterpillars tend to spread out and feed on their own. There may be thousands of caterpillars on a single tree. Small trees are sometimes defoliated completely by mid summer. Even mature oaks may be defoliated to the point that there may be some twig dieback due to sun scald or other factors.
As the caterpillars mature, in late August or early September they drop to the ground and are often seen crawling across sidewalks and driveways, yards, etc. These caterpillars may wander for a considerable distance while searching for a place to pupate. They dig into the soil three or four inches and pupate there. There is usually one generation per year and the caterpillars overwinter as pupae in the soil.
Control is complicated by the size of many of the infested trees. Fortunately, late summer defoliations are much less damaging to the health of trees than early spring defoliations. In most cases it is probably better to rely on birds, diseases and parasites to lower the population next year.
If treatment is deemed desirable, timing treatment to the young larvae is most effective. To determine when young larvae are present, watch for defoliated tips of branches beginning in mid-August. In early to mid-August, one could also put out some white trays or white pieces of cardboard to sample for the frass and fecal dropping out of the trees. Fecal pellets on sidewalks or car hoods are often an early clue. Detecting caterpillars before they are large enough to notice in the trees allows application of insecticide before the caterpillars do much damage.
For "greener" control, use B.t. while larvae are young, or if possible, knock the caterpillars off the trees. Shaking limbs with a pole or by rope will cause the caterpillars to drop to the ground. If the tree is ten inches or less in diameter you may be able to thump on the trunk enough to create a rain of caterpillars! Cover your head! If this is a perennial problem, one can enhance the predator population by installing wasp nest boxes nearby in the spring.
Trunk injections of powerful systemic insecticides are effective if done properly,
though the need for this measure would be rare. Consult the NC
Agr. Chemicals Manual (see link below) for other chemicals.
(Orthene TTO,*various Ortho products)
|Follow label directions|
|*Bacillus thuringiensis; B.t., Dipel, Thuricide, others)||Apply to foliage adjacent to web.|
|chlorantraniliprole (Acelepryn)||Foliar or soil drench systemic|
|*carbaryl (Sevin)||Follow label directions. Apply to adjacent foliage.|
|spinosad (Conserve, *Fertilome Borer & Bagworm)||Follow label directions.|
|bifenthrin (Talstar Lawn&Tree)||Follow label directions. Apply to adjacent foliage.|
* formulations suitable for home use.
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Recommendations for the use of chemicals are included
in this publication as a convenience to the reader. The use of brand names
and any mention or listing of commercial products or services in this publication
does not imply endorsement by the North Carolina Cooperative Extension Service
nor discrimination against similar products or services not mentioned.
Individuals who use chemicals are responsible for ensuring that the intended
use complies with current regulations and conforms to the product label.
Be sure to obtain current information about usage and examine a current
product label before applying any chemical. For assistance contact an agent
of the North Carolina Cooperative Extension Service in your county.
© 2001 NC Cooperative Extension Service
Stephen Bambara, Extension Entomologist
Photos by J.R. Baker, Lance Risely & James Solomon forestryimages.org, and S. Bambara
ENT/ort-139 September 2006
Web page last reviewed January, 2011 by webperson.