6 Woodlot Pests to Look Out For

Some woodlot pests are out to eat into your cash flow. In up to three seasons, they can destroy trees that took 15 or 20 years to grow and are nearing profitable maturity.

Chief among the insect pests are the Asian longhorned beetle; emerald ash borer (EAB); hemlock woolly adelgid (HWA); brown marmorated stink bug (BMSB); residual Gypsy moth populations; and, despite its name, southern pine beetle (SPB), which has been found North into New England.

Be on the lookout for spotted lanternfly and thousand cankers disease, according to Sven-Erik Spichiger, entomology program manager for the Pennsylvania Department of Agriculture.

Asian longhorned beetle

Thousand cankers disease will ruin black walnut trees. It is a joint effort of a fungus (Geosmithia morbida) and walnut twig beetles. Symptoms of infection are yellow wilting and pinholes on the twigs. The pest is in southeastern Pennsylvania and Cecil County, Maryland.

“Thousand cankers will have good years and bad,” Spichiger said, noting that last year even infected trees looked good. However, in some years foresters found 6,000 beetles on a single tree.

The spotted lanternfly attacks Ailanthus (Tree of Heaven) and grapes and up to 30 other species. Lanternfly lays eggs in masses like muddy Gypsy moth clumps.

Movement of infected material – including limbs and cuttings – is illegal.

Thousand cankers disease/Walnut twig beetle

1. An Asian longhorned beetle success story

New Jersey is among a handful of areas that eradicated Asian longhorned beetle.

“The biggest problem with Asian longhorned beetle is we don’t have good controls since it lives deep in trees,” said Kelli Hoover, professor of entomology at Penn State University. “They are not out long as adults.”

An introduced insect from China, it harbors a rich diversity of gut microbes, including bacteria and fungi. Treating trees with systemic materials results in uneven results since the beetle lives deep within huge trees.

“We are broadly interested in the hypothesis that microbial symbionts in cerambycids drive host range,” Hoover said. Currently, she is investigating mechanisms of resistance against this beetle to determine if plant secondary metabolites act directly against the gut symbionts or indirectly through negative impacts on the beetle itself.

Spotted Lanternfly

Hoover’s team is also looking at semiochemical communication in the Asian longhorned beetle. The term “semiochemical” includes pheromones, allomones, attractants and repellants within a species or between species. Currently, researchers are studying a long-range, male-produced pheromone and a sex-specific, female-produced trail pheromone.

“We are also involved in providing input to the technical panels on development of appropriate treatment schedules and guidance manuals,” Hoover said.

The Asian longhorned beetle is a major problem in Germany, Austria, England and Italy.

2. Southern pine beetle

Until recently, southern pine beetle with its associated blue-stained wood was considered to be restricted largely to the southeastern states. But it has been found as far north as Connecticut.

SPB is not a species of federal regulatory concern. Still, the Connecticut Department of Energy and Environmental Protection’s (DEEP) foresters want to contain it.

Foresters in the southeastern United States found that, in general, managing a stand for the health of individual trees appears to be the best way to keep SPB in check. In stands of pitch pine, thinning to release pitch pine crowns from competition might be the best way to protect them from outbreak attacks of SPB.

Southern pine beetle (SPB)

For landscape trees, bark drenches can help prevent attacks on trees when the beetle is in outbreak mode. Trees that have already been attacked and show the blue-stain fungus in the sapwood cannot be saved as there is no treatment for the fungus. Drenching a forest full of trees is not practical.

Woodlot owners and Christmas tree growers are encouraged by DEEP foresters to use proper sanitation when working with blue-stained wood. Hand saws, limb loppers and other equipment should be cleaned as there are indications that the fungus can be carried to healthy trees by infested tools.

Wood from infested or killed trees can be used in solid-sawn form, provided the tree has been debarked to remove remaining SPB beetles. The blue-stain fungus is not a decay fungus and does not weaken the wood. It may, however, decrease the appearance value of that wood.

At the moment, Connecticut foresters say their best recom- mendation is to chip any SPB infested trees on-site and remove the chips produced off-site, at some distance from any potential host trees. It is considered unlikely that many beetles would survive the chipping process. Double-chipping and composting would help further diminish the likelihood that the beetles would survive.

Hemlock woolly adelgid (HWA)

3. Hemlock woolly adelgid

Hemlock woolly adelgid is an aphid-like insect that previously had caused little damage to native Asian hemlock species. However, its introduction from Japan into the eastern United States was a game-changer. Native hemlocks lack resistance to HWA (pronounced “adele-jid”) and, as a newcomer to northeastern forests, it had no natural predators.

“They multiply without having sex. Female adelgids pump out babies like aphids do,” Hoover said. While Northern winters knock them down, last year was mild and may result in a population boom on Eastern and Carolina Hemlock. HWA is most serious in the South where swaths of forest in the Smokies are denuded.

Emerald ash borer (EAB)

Today, HWA can be found from southeastern Maine down through the bottom of New Hampshire and Vermont; in Massachusetts, Connecticut, Rhode Island and New Jersey; and into much of Pennsylvania, Maryland and West Virginia; and down the Appalachian Mountains at a rate of about 20 miles a year.

HWA has a needle-like stylet that jabs the base of hemlock needles and sucks out the tree’s energy reserves. Looking at the underside of a hemlock branch (the side with the needle stripes), one sees white globs of HWA. The resultant stress results in needle loss and eventually kills the tree. It takes from two to six years for HWA to kill a hemlock.

As with most insect pests, wind, birds, animals and human activity distribute HWA. In those broad swaths of forest with hemlock, early detection is important. If you are planting hemlock seedlings, be sure to buy from a nursery that is not in a HWA-infested area or one that has inspected its trees.

Spotting the problem early will help if pesticides are being used; however, once HWA is into a woodlot, it will be difficult to eliminate. One non-pesticide practice that will help is to avoid hanging bird feeders on hemlock trees. Foresters are trying to release predator beetles of the species Laricobius nigrinus to control the problem. Another predator, from Japan, is Laricobius osakensis. Hoover said she is hopeful about natural predators but notes it will take time before they can be released.

Brown marmorated stink bug (BMSB)

4. Emerald ash borer

“Once emerald ash borer gets into an area, you will see 99 percent mortality in three years,” said Spichiger.

EAB has killed more than 40 million ash trees across a wide swath of the country, starting in New England, and ranging down through New York, Pennsylvania, West Virginia, Maryland and Virginia and into Michigan, Ohio, Indiana and Illinois. Even states as far as Missouri, Wisconsin, Minnesota, Kentucky, North Carolina, Georgia and Colorado have EAB. Hoover said she has not seen a single ash tree in Centre County that has not been hit by EAB. According to the Pennsylvania Department of Agriculture, EAB likely arrived in North America in wooden shipping crates, and was first detected in southeastern Michigan and Windsor, Ontario, Canada. EAB beetles will kill an ash tree within three years of the initial infestation.

Asian Gypsy moth

EAB has a vivid emerald color. Adults are dark green, a half-inch long and 1/8-inch wide. They fly from early May until September. Larvae spend the rest of the year beneath the bark of ash trees. When they emerge as adults, they leave D-shaped holes in the bark about 1/8-inch wide.

Spichiger recommends landowners inventory ash on their property. Ash along farm lanes and hedgerows can be a hazard as dead trees fall.

The state does not have a quarantine on ash but the federal quarantine on the EAB and external quarantines on firewood from outside the state are still in effect. This means it is legal to move firewood, ash and the insect between counties inside the state, but it is not legal to move noncompliant items out of the state, nor is it legal to move noncompliant firewood into the state.

Thus, the major thrust for EAB control: keep firewood sales and purchases local.

If a tree loses 50 percent of its canopy, it is probably too late to save the tree. Studies show it is better to begin using insecticides while ash trees are relatively healthy, because most insecticides for EAB are systemic. The tree needs to be healthy enough to move the material up the trunk and into the canopy. Imidacloprid should be applied when soil is moist but not water-logged. Many EAB materials are trunk-injected and should be applied from early May to mid-June. Other materials like Merit, Xytect and Bayer Advanced are soil drenches and can be applied in mid-fall or mid-to-late spring.

EAB has had a couple of tough winters that knocked it back a bit, Spichiger noted. However, he said he expects populations to be a bit stronger this year due to the milder winter.

Read more: Insects and Diseases in the Woodlot

5. Brown marmorated stink bug

Brown marmorated stink bug, a relative newcomer, was first collected in Pennsylvania in late 1998 but now Halyomorpha halys is found across much of the state. It also is found in New York, New Jersey, Connecticut, Massachusetts, New Hampshire and Rhode Island. BMSB can appear at any time from warm, sunny periods in winter through the spring and summer months.

“Marmorated” means striped or veined like marble. Adults are the typical shield-shape of stink bugs, almost as wide as they are long. They have light bands on their antennae and darker bands on the overlapping front pair of wings. Most have patches of copper-colored or bluish metallic depressions around the head and pronotum. Their eyes are deep red. The abdomen is yellow-red in the first instar, progressing to off-white with reddish spots in the fifth instar.

BMSB feeds on all sorts of fruit trees, ornamental plants and even soybeans and sweet corn. On apple trees, it creates a look known as “cat facing” (because it looks like a cat’s face), which makes the fruit unsuited for fresh market sale.

Spichiger noted it took 10 years for BMSB to show its true distribution potential and it now ranges over half the country.

“Most areas will see it cycle every five years or so, tied to the weather,” Spichiger said. It is doubly difficult to predict since there are no scouting programs for BMSB.

If necessary to treat for BMSB, a synthetic pyrethroid like deltamethrin, cyfluthrin, lambda-cyhalothrin, cypermethrin, sumithrin or tralomethrin should be applied by a licensed applicator. Unfortunately, any activity by the chemical probably will fade in a week’s time, making application economically feasible only in specific cases.

Basic controls

There is no silver bullet for controlling insects. As with most other insect predation challenges, keeping trees healthy and vigorous will make them more likely to survive insect attack.

Prune trees. Removing dead branches will reduce the cover for the pest’s larvae and pupal stages. Get rid of large brush piles or stacks of wood that can serve as shelter for larvae. However, leave enough low material around that shrews and mice will feel comfortable hanging around – they prey upon pests like Gypsy moth.

Plant trees not on the preferred menu of local insect pests.

6. Gypsy moth

Gypsy moth is still an important insect pest across the Eastern United States.

While oak remains its favorite target, Gypsy will feed on aspen, birch, linden, sweetgum, crabapple, hawthorn, mountain ash and willow trees. Some trees – red and silver maple, green and white ash, dogwood and tulip tree – are resistant. Evergreens are generally resistant although Gypsy moth caterpillars have done a number on blue spruce and white pine trees.

Gypsy moths overwinter as eggs that hatch as trees begin to pop their leaves in May. The female lays masses of 1,000 or more eggs – making it one of the most destructive foliage-eating pests.

Egg masses are attached to trees to mailbox posts to barn siding. Newly hatched caterpillars climb into the tree canopy and munch away. One Gypsy moth caterpillar will consume two to three dozen leaves each day. When they hit their stride in late June or early July, it can seem that an infestation can eat every leaf on a tree overnight. After they complete feeding, they enter the pupal stage, producing adult moths in 10 to14 days.

A normal outbreak of Gypsy moth will last two or three years until either predators, disease or a population crash brings them under control. Many landowners, and even county programs, have had success with Bacillus thuringiensis, commonly called Bt, a naturally occurring microorganism that requires good timing to be effective. Dipel and Thuricide are two brand names. Bt produces a crystal protein toxin that kills the cells lining the insect’s gut. Since insect guts are only one cell layer thick, the toxin eats a hole in the gut, causing an infection in the body cavity, and death.

Read more: Firewood and Invasive Pests

Photo: FYMStudio/iStock