White oak decline evident this year in West Virginia

CHARLESTON, W. Va. — Extensive white oak decline and mortality has been observed in several areas of Wood County. A local forester, Jack Mathers, working for Haessly Timber and Logs in Marietta, Ohio, had been tracking this decline for several years and brought it to the attention of the West Virginia Department of Agriculture and the USDA Forest Service.

The WVDA, Forest Services and Mathers recently spent a day looking at several areas where this decline is occurring. One of the first things noted was that trees had substantial evidence of jumping oak gall wasp, Neuroterus spp., on the leaves.

Wasp outbreak

In 2010, there was a severe outbreak of jumping oak gall wasp in Cabell, Jackson and Wayne counties and in previous years, there have also been reports from other counties including: Harrison, Doddridge, Ritchie, Wood, Kanawha, Putnam, Roane, Gilmer, Wirt, Calhoun, Lewis, Braxton and Clay.

“Surveys are underway now to document areas of jumping oak gall wasp and oak decline,” said Agriculture Commissioner Gus R. Douglass. “At this time, we don’t know how wide-spread the problem is.”

What happens

These wasps lay eggs in the tissues of new oak leaves in the spring. Each gall contains a single immature wasp. The young galls look like small, green, flat buttons that turn brown as they mature. When mature, the galls fall off the foliage leaving small pits in the underside of the leaves where they were attached.

If there are numerous galls on the leaf, the entire leaf usually turns brown and falls off. Once on the ground, pupation occurs. Second generation adults overwinter inside the galls and will emerge next spring. The wasps are very tiny (1.0-1.5 mm long) and do not sting.

Result

White oak can usually withstand one or two defoliations. But, if this has been occurring over several years with the trees undergoing multiple defoliations, the trees will eventually succumb to the stress.

“This stress leaves the tree wide open for secondary agents such as Armillaria root rot and Hypoxylon canker to establish along with other decay fungi and secondary insects such as wood boring insects,” said WVDA forest pathologist Jill Rose. “This causes further decline of the tree and, eventually, death.”

If you notice any major outbreaks of oak decline, contact the WVDA Plant Industries Division, 1900 Kanawha Blvd., East, Charleston, WV 25305-0191 or call 304-558-2212.