Monday, September 16, 2013

Scattered yellow-poplar decline reported across Lee, Wise and Scott counties

Recent declines in yellow-poplar in Lee, Wise and Scott counties have landowners concerned over the health of one of the most abundant and resilient hardwood trees in Virginia’s forests. While not entirely certain about the reason for the declines, Virginia Department of Forestry personnel believe they may stem from past insect infestations that previously went unnoticed.

Yellow-poplar, or tulip poplar, is the most common hardwood tree in Virginia and one of the most important timber species in far southwest Virginia. Its rapid growth, straight trunk and wood properties, along with its abundance, make it an excellent tree for loggers to harvest in bulk and bring to the mills. Generally speaking, yellow-poplar is a resilient tree that does particularly well in moist cove habitats and fertile soils common to the lower slopes and valleys of the southern Appalachians. It also has very few insect and disease problems due to the fact that the leaves, bark and wood contain a host of chemicals that deter them. Even an invasive species like the gypsy moth, which can feed on more than 200 species of trees and shrubs, will completely avoid feeding on yellow-poplar.

“Two notable exceptions to this rule, however, are native insects known as the tulip tree scale and the poplar weevil,” said Bill Miller, senior area forester with the Virginia Department of Forestry. “The scale is a tiny sap-sucking insect that produces a brown, waxy covering that looks something like a tortoise shell. Populations of these insects can occasionally reach such high levels in the forest that they can damage and even kill poplar trees, although this is rarely seen in southwest Virginia.”

On the other hand, the poplar weevil is a defoliating insect that is particularly common in southwest Virginia, especially in Lee, Scott, Wise, Dickenson, Buchanan, Russell and Washington counties, along with adjacent counties in Kentucky and Tennessee. In most of these counties, as many as six to eight poplar weevil outbreaks have been documented over the last 25 years by forest health personnel with the Virginia Department of Forestry. Feeding by individual weevils in spring causes little damage to newly emerged leaves, other than a small brown patch. During outbreaks, however, millions of weevils can result in poplar trees being heavily defoliated. These outbreaks are often patchy in nature but can span large areas.

VDOF Forest Health Specialist Dr. Chris Asaro said, “While the word ‘outbreak’ can sound very dramatic, the truth is that these defoliation events are often not noticed from the ground for several reasons: they are very patchy across the landscape and often occur in remote areas that are not easily visible. In addition, poplar trees are generally quite tall and most people driving by don’t have the tendency to look up. Furthermore, while complete defoliation of poplar can occasionally occur, trees with adequate moisture often leaf out again pretty quickly, erasing any evidence of past damage. Outbreaks typically don’t last very long in any one area either because poplar weevil has a host of other insects that prey on them, which usually causes outbreak populations to crash after a year or two.”

While one defoliation event by itself is probably not going to cause poplars to decline or die, several defoliation events over successive years can weaken trees and, combined with other stressors such as drought, lead to some localized dieback, decline or even death. Recently, some landowners across Lee, Wise and Scott counties have seen such poplar decline over the last few years and have expressed concerns to local foresters. In most cases, these areas of decline are small – generally from ½ acre to several acres in size – although several locations have exhibited decline spanning 50 acres to 100 acres.

“There appears to be no obvious reason why these declines show up where they do, other than the fact that these areas were known to have several weevil outbreaks during past years,” Asaro said.

“Because tree decline is a gradual process that can take many years and be caused by multiple agents, it’s always difficult to pinpoint exact causes. But knowing that the weevil is a major presence in the region and one of the few insects that can feed on poplar, it seems very possible that it is playing a prominent role in these decline events,” Asaro said.

The good news is that the affected areas are quite small, and most of the poplar trees are weakened but not dead. That means the wood is probably still sound and can be salvaged, so most landowners can still profit from forests with some poplar decline. Forest landowners concerned about their poplar stands should consult their local Virginia Department of Forestry office for further information and advice.

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