Whether as part of a maple sugaring stand of trees, future timber sale, silvopasture system or overall land management, it pays to know how insects and disease affect your trees. At the recent New York Farm Show, Kim Adams, Ph.D., entomologist with the SUNY College of Environmental Science & Forestry, presented “Tree Health: Insects and Diseases of Concern in New York in 2023.”
In her 20 years presenting at the Farm Show, Adams has seen different insects phase in and out of concern. But one of the constants of her work is asking landowners why they own forest.
“That makes a difference in how you approach all these things,” she said. Ownership objectives can include aesthetics, investment, maple syrup or other forest products, recreation, timber, water quality, wildlife habitat and preservation and more.
Just as with crops, not all trees grow well at all sites. “Most people see if it’s brown on the bottom and green on the top, and that’s all that matters,” Adams quipped. “Appreciate the site and what the insects and diseases will tell you.”
In the northern hardwood region, forest tent caterpillars affect sugar maple trees, quaking aspen, red oak and black cherry trees, among other species. As native, whole-leaf defoliators, these pests leave obvious damage from their handiwork: piles of leaf debris below the trees and few leaves on the tress.
Wintertime is a good time to scout as the bare trees show egg masses on the ends of last year’s twigs. They may be spotted by using binoculars while standing on the ground.
“They have a narrow window in which they can be successful,” Adams said. “Timing can be slightly off.”
The friendly fly, also called the parasitoid wasp, is a naturally occurring predator of the forest tent caterpillar. Although they cannot bite humans, they attack the caterpillars. “These keep outbreaks from getting bad,” Adams said.
Sometimes, landowners mistake a tree disease for an insect because the effects appear similar – such as Anthracnose, a group of fungal pathogens that overwinters and thrives in cool, wet springs.
“It can be enough to defoliate the tree, but not generally,” Adams said. “It can take a while.”
A maple syrup maker seeing his trees defoliated may not suspect it’s fungus. Another pest affecting sugar maple trees is the sugar maple borer. “It looks like wasps, but they’re beetles,” Adams said.
Since she has never captured them in the wild, Adams isn’t convinced it’s a widespread problem. But it’s still important to note the presence of a sugar maple borer.
“When a beetle goes into a tree, a sugar maple ‘bleeds,’” Adams said. “The big thing a sugar maple borer will tell you is the tree is not on the best site or the tree is stressed.” The holes are bullet-shaped and oblong.
The insect identifying stressed trees can help maple sugarmakers know which trees to pay attention to and whether to treat or cull. Since the presence of the borer can indicate an unhealthy tree, by extension, this can mean that the site is not ideally suited for sugar maples, which thrive on rich, loamy soil, not rocky soil with poor drainage. The borer’s persistence may help a landowner decide to shift attention to a different area of the farm for setting up a maple stand or change the operation altogether.
The first year of the borer’s two-year lifespan, it goes horizontally around the trunk, leaving a mark. The following year, it goes vertically up the trunk. Fortunately, woodpeckers devour many sugar maple borers. Their signature pecking holes also can help alert landowners of the presence of the borer. Most of the time, healthy trees survive the borer’s attack but maintain a lifetime scar as a reminder of the pest’s presence.
“The populations aren’t large at this time,” Adams said. “They do not destroy the tree, but they’re not helping its economic value. Trees can survive for decades with this car. It disrupts the conduction.”
The maple leaf cutter represents another maple pest. This tiny caterpillar is seen sporadically but it can damage trees. Adams said to look for leaves with multiple circle-shaped holes, which is where the maple leaf cutter has been feeding. The maple leaf cutter can overwinter.
Pear thrips are also a very small insects. It can damage fruit trees and sugar maples. “It gets started very early,” Adams said. “It feeds in the buds when softened, but not opened.”
The pest produces one generation annually. Look for shrunken-looking leaves mottled with yellow and brown and possibly blisters. Trees affected by pear thrips will lose their leaves prematurely in autumn.
A recurring pest has resurfaced to damage beech trees: beech bark disease. Adams said that the American beech “gets a bad rap in the Northeast if you’re growing for timber. But with the absence of chestnut and oak, it’s ecologically important.”
The current manifestation of beech bark disease is the second iteration in Adams’s lifetime. The disease is caused by insects that chew through the bark which predisposes trees to two canker fungi and kills a small area on the bark. The diseased areas eventually girdle the tree and kill the upper canopy and eventually the tree.
“It looks like pockmarked bark,” Adams said. “The spores are red.”
She also warned about beech leaf disease. It has been identified in New York across the western half the state, in a few central New York counties and throughout downstate. The disease causes leaves to die, and eventually the tree will follow. It’s caused by microscopic nematodes that may be native; however, scientists remain unsure.
In two to seven years, the nematodes’ damage to the leaves kills the tree. It can take months for saplings and about seven years for mature trees.
“Look up to the canopy for striping on the leaves,” Adams said. “Nematodes are feeding on the leaves. You’ll see curling.” So far, no treatments exist for beech leaf disease.
The spongy moth (formerly called the gypsy moth) affects oaks, the pest’s favorite food. In their absence, the spongy moth will move on to other trees, even evergreens. Adams encouraged landowners to treat them before a full outbreak occurs.
“Look for pieces of foliage on the ground,” she warned. “Scout your trees.”
The spongy moth leaves behind egg masses in soft, white material that looks like a sponge. “Spray while they’re still young,” Adams said. “Insecticide won’t work well when they’re mature.”
She encouraged attendees to research their particular tree issue on Cornell’s Plant Disease Diagnostic Clinic at plantclinic.cornell.edu.
by Deborah Jeanne Sergeant