Update on the Health of the Urban Forest

Last Friday, Jim McGlone, Urban Forest Conservationist with the Virginia Department of Forestry gave a “Forest Health Update” to the Potomac Watershed Roundtable. In Northern Virginia we have seen oak trees brown and lose their leaves this summer. Dr. McGlone reports that it is NOT Oak Wilt, Sudden Oak Death nor Ambrosia Beetles. What this appears to be is a continuing of the Oak decline or oak distress syndrome that has been in the area since 2000.

The oak trees may not be dead. Do not cut them down, rather give them a chance to come back. Oak distress syndrome is a slow-acting disease complex that involves the interaction of predisposing factors, inciting factors and contributing factors. No single cause is responsible for the decline. According to Dr. McGlone the predisposing factors are: bad soil/ soil compaction, climate, tree age, wrong tree species for the location and bad genetics. Older trees, those that are more than 70 years old and live on drier sites such as shallow, rocky soils have been the most affected. The inciting factors are: drought, defoliation and frost. These factors reduce the tree’s ability to fight off insect and disease pests and make them more susceptible to future disturbances. They initiate decline by reducing growth, depleting the tree’s stored food reserves, and/or causing dieback. Finally, contributing factors such as secondary insects or diseases that ultimately kill the tree. Finally, the contributing factors to the decline are things such as sapwood borers, sapwood fungus, and root rot.

Dr. MGlone recommends trying to save garden ornamental trees by cutting back the grass cover in the root area and mulching as large an area as you can tolerate. Do not fertilize because it will cause new branch growth and compete for the starch created and stored in the roots needed to support continued tree metabolism. Trees are after all living organisms.

Other threats to our urban forests are the previously discussed emerald ash borer which has spread to just about every county in Virginia. (see a previous article for more details.) Other threats are:
The hemlock woolly adelgid, a tiny sap-sucking insect related to aphids, is causing widespread death and decline of hemlock trees. The adelgid looks like bits of cotton on the hemlock needles.

Laurel wilt, a disease is caused by a pathogen carried by the redbay ambrosia beetle – and by humans moving infested wood. This is an invasive species brought to this country in 2004 at the port of Savanah. The plants at risk from laurel wilt are sassafras, spice bush, red bay, bay leaf, and avocado.

The newest bad bug to arrive on the scene in Virginia is the spotted lanternfly, which is not a fly, but an aphid. This bug was first detected in Virginia in January 2018. This pest destroys grapes, peaches, hops and apples. The Virginia Department of Agriculture and Consumer Services (VDACS) has established a Spotted Lanternfly Quarantine for Frederick County and the city of Winchester to try and slow the spread of the spotted lanternfly to uninfested areas of the Commonwealth.

Look for the distinctive bug to help. In late fall, adults will lay egg masses on host trees and nearby smooth surfaces like stone, outdoor furniture, vehicles, and structures. The quarantine is to prevent the infestation from hitching a ride on your vehicle and infesting other parts of Virginia. It is believed that the spotted lanternfly arrived in Virginia on a load of garden stones from Pennsylvania which has a widespread infestation. You can help stop the spotted lanternfly in Virginia by abiding by the quarantine and helping Virginia Cooperative Extension track its spread. The pictures below are from Viginia Tech as is the video above.