UF/IFAS Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972-2578

Phone: (863) 763-6469

E- mail: indianco@ufl.edu 

Quick Linksdamage photos    eggs    caterpillars    pupa     moth   cultural management    pesticides  UPDATE!   references 

September 21, 2005

Feature Article - for release the week of September 25, 2005

Dan Culbert - Extension Horticulture Agent

What’s Chewing my Oak Tree?

As if our local trees have not had enough damage from last year’s storms, several office visitors have recently asked for help in getting rid of a critter that seems to be eating up many oak trees.  While the Pinkstriped Oakworm is not a new pest to our area, it seems to have captured the attention of several homeowners, and is a good subject for this week’s lawn and garden article.

Damage Photos

left and right:   property owners who notice thinning foliage on their oak trees might take a closer look for caterpillars (photos by Dan Culbert)

 
(left) Early leaf damage by caterpillars shows the skeletonizing, but as caterpillars get bigger, they eat the whole leaf. 

 

(right) look for cluster of eggs - these have hatched.  (photos by Dan Culbert)

According to UF Entomologist John Foltz, there are several caterpillars that can chew off the leaves on local oak trees.  When caterpillars are numerous, they can quickly strip trees of their foliage.  Most serious outbreaks occur in late summer to fall. While oak trees in forests generally survive these invasions, greater damage is noted in urban areas, where leaves become ragged or disappear, and the bugs and their waste material is a nuisance.

The Pinkstriped Oakworm (Anisota virginiensis) can be found throughout the eastern US and up into Canada.   In Florida, there are two other related species of these oak-eating silk moth caterpillars that differ in color.  The caterpillars now seen in local areas are greenish brown with four pink stripes running the length of the body. Their heads are fairly large and green in color. These oakworms can grow to about 2 inches long, and have a pair of long, curved black "horns". 

pinkstriped oakworm, Anisota virginiensis  (Lepidoptera: Saturniidae) Caterpillars can consume oak leaves, but rarely cause long-term injury to local Laurel and Water Oaks, a preferred food source of Anisota virginiensis. Photo courtesy of  Lacy L. Hyche,  Auburn University Pinkstriped Oakworms have a big greenish head, a pink stripe running the length of the body, and two non-stinging black "horns". Photo courtesy of  James Solomon, USDA Forest Service. . The oakworm will over winter as a pupa in the soil.  Photo courtesy of  Lacy L. Hyche,  Auburn University

 

During cooler months, the oakworms rest in the soil as dark brown pupae.  The adult moths emerge in late spring.  They appear brownish red with a purplish tint on the front wings with a small white dot.  Moths are about 1 inch nose to tail and up to 2 inches wide with wings extended. At rest, the wings are usually folded back over the body.  Once they mate, the female lays egg clusters under the leaves, and the little critters begin to chew up leaves for 5 to 6 weeks.

 

Adult Pinkstriped Oakworm caterpillars change into this Silkworm Moth. (This red-colored one is a male.) Photo courtesy of  Lacy L. Hyche,  Auburn University Another photo of an adult Oakworm moth. Note the  color shading of this female is orange/pink different from the male. Both have white spots on the front wings.  Photo courtesy of William T. Hark, M.D. Egg clusters of oakworms are found on the underside of oak leaves.  Photo courtesy of  James Solomon, USDA Forest Service.

Cultural management

Oakworm populations can become large enough to completely strip trees.  Most oaks can handle one such defoliation with little impact on their health.  However, repeated defoliations will weaken the trees and lead to infestation by secondary pests and diseases. Trees that have been stressed by flooding or wind are more likely to suffer from oakworm feeding.

Here are some steps for promoting tree vigor and reducing oakworm insect populations:

·        Provide appropriate water and nutrients to the tree throughout the growing season.  Avoid over or under applications of both irrigation and fertilizers which may stress the tree and make it more attractive to caterpillars.

·        Watch for the moths and look for clusters of small yellow bumps under the leaves. Remove these eggs and the young colonies of worms from the lower branches. Trim them off, smash them, or bag them with household waste disposal – not yard trash.

·        If large numbers of caterpillars are too high for hand removal, contact a pest control operator for application of an appropriate insecticide.

 

Pesticides

Use of insecticides containing Bacillus thuringiensis (Bt) can reduce caterpillar populations with little impact to other beneficial insects.  Other chemical insecticides  can also be used, but many of these homeowner products can kill the good with the bad, so careful application is imperative. Be sure to always read and follow all label directions when using any pesticide.

The timing of sprays is also important.  Smaller caterpillars are easier to manage than larger caterpillars, so quick action after initial identification will reduce leaf loss.  And, a second application of insecticide within a month of the first outbreak may help reduce the second generation of these hungry worms.

Larger trees can probably cope with some leaf loss; however, trees that are stressed and smaller, younger trees are better candidates for insecticidal treatments.  If larger trees are to be sprayed, consider that a licensed pest control operator has the power equipment needed to reach to tops of tall trees.

As with any pest control program, identification of the pest is the first step.  If you suspect that oakworms are taking your oaks out to lunch (and dinner) place a few live, unsmashed worms into a bag or other container and bring them to our office for positive ID.  Don’t leave them sitting on your dashboard in the sun, as cooked caterpillars are a bit more difficult to identify than fresh ones.  Those with digital cameras that can get up close and personal can send us a photo of your offending bug.  We will be happy to identify them for you – and if we can’t, we can send them on to other University of Florida faculty that will be able to tell us what’s bugging your oak trees.

I’ve placed more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on oak tree caterpillars, email me at indianco@ufl.edu or call 863-763-6469.  Local residents can stop by our office at 458 Hwy 98 North in Okeechobee

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UPDATE 10/12/05

(photos by Dan Culbert)

During a recent visit to a local ranch, I observed a large number of moths congregating under a light post.  Several other UF/IFAS Extension agents have also reported recent heavy infestations of Laurel oaks in the south-central Florida area from this insect.  

According to UF Entomologist Dr. John Foltz, "there is a potential for another batch of caterpillars and defoliation this year.  People who had trees heavily defoliated in August-September ought to monitor their trees for another generation in October and November.  Depending on tree species, tree vigor, and caterpillar population, some may wish to apply an insecticide to maintain foliage and tree health.  

Since there is a possibility of a third generation of feeding this fall on our oak trees, follow the management suggestions above.  This will help to reduce populations of over wintering pupa, and reduce damage next spring.

 

references

Anonymous.  Oakworms.   Atlanta: USDA Forest Service, Forest Health Protection, Southern Region. Undated. http://www.fs.fed.us/r8/foresthealth/idotis/insects/oakworm.html 

Foltz, J. and Mayfield, B. "Pinkstriped oakworm abundant in central Florida"  Gainesville: UF/IFAS Pest Alert, 10/14/05. http://pestalert.ifas.ufl.edu/pinkstriped_oakworm.htm 

Hyche, L. L.   Pinkstriped Oakworm Anisota virginiensis (Drury) (Saturniidae). Auburn: Department of Entomology & Plant Pathology, Auburn University, 2/2000  http://www.ag.auburn.edu/enpl/bulletins/pinkoakworm/pinkoakworm.htm 

Serrano, David and Foltz, JohnYellowstriped Oakworm in Gainesville, Florida  Anisota peigleri.   Gainesville: UF/IFAS  June, 2002. http://eny3541.ifas.ufl.edu/oakworm/Anisota_peigleri.htm 

Struttmann, Jane M.  Pink-striped oakworm moth (Anisota virginiensis) (in: Moths of North America).  Jamestown, North Dakota: Northern Prairie Wildlife Research Center, 2005. http://www.npwrc.usgs.gov/resource/distr/lepid/moths/usa/953.htm