We continue to rate the General
Condition of sugar maple by an annual
evaluation of 2000 trees. Defoliation by
the forest tent caterpillar has adversely
affected tree health in some regions. For
the first time in a decade, less than 90%
of sugar maple trees were healthy on
our survey plots.
Forest Tent Caterpillar populations
increased in 2006, with 343,000 acres of
defoliation mapped by aerial survey.
The damage generally increased from
2005 in southern Vermont and in the
central Green Mountains, and decreased
in the Champlain Valley.
Large numbers of caterpillars died from
disease. Many others died in cocoons
thanks to parasites, such as the native“friendly flies” that were so common in
early summer. Still,
the outbreak may
continue in 2007.
Forest tent caterpillar
moth counts are about
the same as they were
In winter 2005-06, 209 sugarbushes
were surveyed for forest tent caterpillar
egg masses. Defoliation was redicted
in two-thirds of them.
Although healthy maples can withstand several years of defoliation, some are declining in
sugarbushes which have been defoliated two or three times. Dead trees are showing up in
recently thinned sugarbushes, or on ridges, dry slopes or wet areas. Some unthinned trees on
good sites have also died.
Saddled Prominent populations
increased noticeably in the northern
Vermont region which has not been
affected by forest tent caterpillar.
Defoliation was mapped on 1,340 acres in
Essex, Orleans, and Caledonia Counties.
Saddled prominent caused a lot of sugar
maple dieback in the early 1980s. It does
most of its feeding in July. Sampling in
the spring can help predict whether or not
the insect may be a problem.
The foliage of many sugar maple trees
turned brown in September because
they had been infected with the fungus
disease, Anthracnose. Leaves were
infected during earlier wet weather.
Damage was worse on lower branches,
near wetlands and low-lying areas. The
impact on tree health shouldn’t be
serious, since the damage occurred so
late in the season.
Most Lecanium Scale populations
crashed. Scattered sugarbushes still had
a lot of these insects in 2006, with their
honeydew and associated sooty mold.
Sugar maple tree recovery seems good
in areas with a lot of scale in 2005.
Weather Conditions continued to be
good for sugar maple in 2006: a mild
winter, no late frosts, plenty of rain, and
a warm fall. The rain had an upside…it
helped trees recover from defoliation.
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