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Friday - May 30, 2008

From: Austin, TX
Region: Southwest
Topic: Trees
Title: Insect attack on bur oak (Quercus macrocarpa)
Answered by: Nan Hampton

QUESTION:

Something is attacking the bur oak that was planted in 2007. Insects are not on the leaves, but the edges of some leaves look chewed back. Others look brown around the edges. Do you have any idea what we are dealing with here, so that we may treat the tree? Thanks.

ANSWER:

According to an article from the Florida Cooperative Extension Service by E. F. Gilman and D. G. Watson, Quercus macrocarpa (bur oak) is pest resistant. They say: "Pest resistance: long-term health usually not affected by pests" and "No pests are normally serious." They do list various insects that sometimes attack the bur oak. Of the ones they list in the article, the gypsy moth (Lymantria dispar), the oak leafmining sawfly (Profenusa lucifex) and oak kermes, or scale insect, (Nanokermes pubescens) sound as if they are the most likely suspects. According to the article, gypsy moths feed mainly at night and find a place to hide out of the sun during the daytime. If you have a small infestation, this may be why you haven't seen any caterpillars. The gypsy moth article offers advice about control of these insects.

The only photos of the damage caused by the oak leafmining sawfly (Profenusa lucifex) is in French from PHYTO Ressources from Canada. A loose translation of the article is that Profenusa lucifex "is a small fly, whose yellowish-white larva burrows mines between the leaf veins, producing a brown stain on the top surface of the leaves from mid-June till the end of July. Normally, there is a single generation per year. Sometimes there is a second generation that is active in the autumn, but the mines are less numerous. There is no description of the life cycle. It attacks all oak species (Quercus spp.). No control methods, either cultural or chemical are known." There are photos showing the damage on Quercus coccinea (scarlet oak).

Nanokermes pubescens (syn.=Kermes pubescens) is a tiny, nondescript insect that can easily be overlooked. The article, "Scale Insects on Shade Trees and Shrubs" from Purdue University gives more information, photos and control methods.

In an article from the US Forest Service several other pests are named, but none that are named seem to match the damage you see on your tree. The pests are:

Variable oakleaf caterpillar (Heterocampa manteo)

Redhumped Oakworm (Symmerista albifrons)

Phyllophaga spp. attack roots

Oak lace bug (Corythucha arcuata)

Apparently, the bur oak is the only host plant for the oak skeletonizer (Bucculatrix recognita), but there are no photos available on the web of the insect or the damage it does.

If you think your bur oak is in imminent danger, my advice is to contact a certified arborist who can look at it to determine what is causing the problem and offer a solution.