One-fifth of Vermonts trees are sugar maples, making it our most common species. This mighty tree supports the maple sugar industry, accounts for half of Vermonts hardwood timber harvest, sustains foliage season, and shades town greens and backyards.
But is our state tree in good health? On average, yes.
Every year, the Department of Forests, Parks, and Recreation (FPR) looks at tree health from the ground and from the air. All 4.7 million acres of forest land are evaluated from an airplane at least once, more than once if new problems arise. In addition, survey crews walk to 150 forested locations to rate tree condition. In 1998, FPR staff evaluated 2,000 sugar maples. Crews judged only 3 percent of them to be unhealthy, based on how many dead twigs they displayed (Figure 1).
Maple Browning in 1998
Unfortunately, the news was not all good, especially in southern Vermont. Scattered maples over a widespread area had brown leaves due to a fungus called anthracnose. This springs unusually wet weather was ideal for fungus infection. In addition, pear thrips, tiny insects which came here from Eurasia, fed on developing buds during April and May. Damage by pear thrips makes leaves more susceptible to anthracnose infection. In early July, aerial survey crews mapped scattered browning on about 10,000 acres.Normally, defoliated trees would sprout a second set of leaves within a few weeks. However, the long stretch of wet weather allowed anthracnose to blight this refoliation. New leaves developed sparsely, or not at all. In addition, the fungus spread to other trees, and the extent of damage grew. Late in the season, populations of two other insects which turn maple leaves brown, maple leaf cutter and maple trumpet skeletonizer, increased statewide. By late August, the area of brown hardwoods had jumped to 100,000 acres.Trees which are otherwise healthy can tolerate several years of defoliation; most Vermont maples have been healthy in recent times thanks to consecutive years of good growing conditions, and the worst browning was not in areas affected by Januarys ice storm. However, refoliation from 1998s damage was sparse. New shoots and leaves which developed on damaged trees were killed by anthracnose. New leaves which did survive were mostly small and yellow because rainy weather interfered with the absorption of soil nutrients.
A similar situation occurred in Pennsylvania and New York in 1994. Defoliation by caterpillars in June was followed by anthracnose in July. This combination caused severe branch dieback and increased mortality the following year. In one county, more than 30 percent of the maples were dead on 35,000 acres.
Exotic Pest Threatens
Meanwhile, the Asian longhorned beetle is still a serious threat to maple health, even though it hasnt been seen in Vermont. This beetle, which feasts on sugar maples, can kill a tree in less than three years. Based on its distribution in China, researchers believe the Asian longhorned beetle could survive Vermont winters.
Trees infested by this insect were first discovered on Long Island two years ago. In 1998, infestations were also found in Chicago. More than 2,000 trees have been cut down and destroyed to eradicate Asian longhorned beetle from New York. Surveys will continue there, and in Chicago, for several years.
The Asian longhorned beetle has usually entered this country in wood used to pack pipe, granite blocks, and heavy machinery shipped from China. Customs agents have intercepted this beetle in 14 states. To reduce the risk of introducing this beetle to new locations, the U.S. Department of Agriculture has proposed a rule requiring that imported wood packing material be treated before use.
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