Hemlock Woolly Adelgid Control

Hemlock Woolly Adelgid: Tom Coleman, US Forest Service, Bugwood.org

The hemlock woolly adelgid (HWA) has caused significant damage to eastern hemlock, Tsuga Canadensis, in ornamental plantings and forests across much of Pennsylvania. However, many trees are still surviving and in need of treatment.

Description:

The most obvious sign of a HWA infestation is the copious masses of white filaments of wax produced by the females. These "cottony" masses normally persist throughout the season and into the following year, even after the insects are dead. The overwintering females are black, oval, soft-bodied, and about 2 mm long. They are concealed under their characteristic white waxy mass. HWA populations are usually located on the underside of the twigs at the base of the needles.

Life History:

The overwintering adult females begin laying eggs in large clusters in the cottony masses during warm weather in late winter and early spring. They continue to lay eggs into June. Eggs start to hatch in early April, and depending on spring temperatures, hatching is completed by late June. The newly hatched nymphs or “crawlers” become mature by late September and spend the winter on trees as mature females.

Damage:

Host plants are injured by the adelgids inserting their piercing-sucking mouthparts into the base of the needles and removing plant fluids. Moderate HWA populations may cause a reduction in tree health. Severe infestations may result in premature needle drop, reduced twig growth, dieback, or death of trees.

Evaluate Trees:

Not all hemlocks can be saved. It would be too expensive to do so, as insecticide treatments need to be applied every few years. Consider the cost! Also consider the cost of removing dead trees that are near homes and other structures. Treat hemlocks that are the healthiest, most vital to the landscape or forest, easiest to reach with a sprayer, and furthest from sources of water. Remove trees that will NOT be treated to eliminate nearby sources of the insect to re-infest treated trees.

If trees do not have any HWA on them at all, they do not need treating. Insecticide applications are necessary once you see a light infestation or if adjacent trees are infested. This will keep the tree from going into decline. Treating HWA aggressively, while the tree is still in good health, is the best way to maintain a healthy tree. Severely defoliated trees will likely not recover even with treatment.

Treatment:

Try to minimize any stress on the tree. If possible and practical, during periods of drought, water the tree. Do not fertilize infested trees. This only aids the survival and reproduction of the adelgids. Prevention alone does not always work and trees which are infested will usually die unless an insecticide treatment is applied.

Horticultural Oil or Insecticidal Soap: These are the safest insecticides for controlling HWA. They are not toxic, but kill the insect by smothering it as the spray dries on the pest. These treatments are made in the fall from August until it gets too cold to spray. Treating other times of year will result in poorer control of the adelgids and may result in foliage burn. The entire tree, including the bark of the trunk and limbs, is thoroughly sprayed (drenched actually) with this material. A forceful spray is needed to get adequate coverage.

Both of these products are used at a 2% solution (2% solution = 2.6 ounces of spray material per gallon of water). There is no residual control with these materials; once they dry they will no longer control HWA. Trees will probably need to be treated annually. Be sure oils stay well mixed with the water during application. Using these materials is difficult if you do not have adequate equipment, especially on large trees.

Homeowners may be able to spray trees eight feet or smaller with a backpack sprayer or other types of hand held sprayers. For complete coverage, spray until droplets are observed running off. Be sure to spray on the undersides of limbs as well as the top. Every branch must have thorough coverage to get control. Larger trees require a high pressure sprayer and may require hiring a commercial arborist/pesticide applicator.

Soil Drenches: This treatment is effective for large trees that cannot be completely sprayed. The insecticide is applied to the soil surrounding the roots of the tree. The tree roots take up the product and move it into the foliage where the insect is killed. Soil drenches must be applied when there is adequate soil moisture in either the spring or fall. The best time to treat is in March or April. Do not use in areas near streams or ponds or where the soil is exceedingly rocky.

Most soil drenches are made with an imidacloprid product (Merit 75 WP, Malice 75 WSP, Zenith 75 WSP). Any of these can be purchased by the homeowner and applied to their own property. There are other imidacloprid products coming on the market. Any may be used as long as they have a landscape label. Imidacloprid products mentioned above all have 75% active ingredient. An imidacloprid product specifically for homeowners, Bayer Advance Garden Tree and Shrub Insect Control, is more readily available and can be purchased from home improvement stores. The rates of these products are based on the size of the tree trunk or height in the case of a hemlock hedge.

 Elongate Hemlock Scale:Pennsylvania DCNR - Forestry , Bugwood.org

IMPORTANT: If your hemlocks are also infested with elongate hemlock  scale then you must use another similar product, with slightly faster uptake, called Safari 20 SG (dinotefuran). This may also be applied as a soil drench as well as a bark spray. It will control both the scale insect and the adelgid. Safari trunk applications should be made before bud-break or shoot elongation in the spring.

Homeowners: (READ the LABEL!) Use Bayer's Advance Garden Tree and Shrub Insect Control for soil drenches.

·         Measure at chest height the total number of inches in circumference around the tree (if you use Merit, Malice, Zenith, or Safari – measure the circumference at chest level and divide by 3 to get the diameter in inches).

·         Note: Bayer's Tree and Shrub Insect Control will treat 32 inches of trunk circumference cumulatively, (equals approximately a 10 inch diameter tree.

·         One ounce of either Merit, Malice or Zenith will treat 15 inches of trunk diameter at the high rate or 30 inches at the low rate. If your trees are highly infested with HWA, use the high rate, otherwise consider using the lower rate. This can be then be mixed in a bucket with any amount of water to pour around the tree.

·         Safari 20 SG can be used at 1.0 to 4.2 ounces of product per 10 inches trunk diameter. This can be mixed in any amount of water to pour around the tree. It is also labeled for trunk spray on the lower 4-5 feet of the trunk. This is currently the only product labeled as a bark spray. A carefully applied trunk spray may be appropriate where surface water is nearby.

·         Use the following method - dig a shallow trench around the circumference of the tree, 1 foot away from the trunk. Be sure to remove all mulch and other organic material, the insecticide must be applied directly to the soil. Pour product in trench at the correct rate.

For soil drenches to work, the trees must be healthy enough to move the product from the roots up into the foliage. If trees are already in a state of decline, due to HWA, spray as much of the tree as possible with either horticultural oil or insecticidal soap to kill as many of the pests as possible. Then treat the following season with imidacloprid.

Determining Control:

It is not easy to know if HWA has been successfully controlled. The white filaments of wax may still be on the foliage following insecticide treatments. In many cases, it takes examination of the insect under magnification to see if it is dead. The best way to learn if the trees are recovering is to wait until the next flush of hemlock growth to determine if growth has improved. Even when working properly, a soil drench of imidacloprid may take a year or longer to show control. Do not expect instant results, be patient.

Follow-Up Treatments:

Any of these treatments can last anywhere from 1-5 years depending on their success and proximity to infested hemlocks. Successful treatments are usually a function of the initial health of the tree and the amount of soil moisture when treatments were made. Keep monitoring new growth for the white, waxy wool of the adults. Re-treatment is necessary when adelgids are found on many of the branches.

Large Tracts of Hemlock:

In wooded areas with many hemlocks it is not possible to save every tree. If deciding to treat with a soil drench, determine budget for materials and treat trees that are most important to the landscape or important as seed trees. Measure and mark with paint the trees to be treated. Small understory trees can be sprayed with horticultural oil in the fall.

Precautions:

Always read and follow pesticide labels. The label contains other important information not included in this article. The use of any insecticide can have unwanted consequences to the environment. Be sure to follow all label directions. Do not apply insecticides to the soil near surface water such as streams or ponds or where the soil is exceedingly rocky. Only spray trees if the material will not drift into open water such as streams or ponds or onto adjacent property. Do not exceed labeled rates of products. Applying a higher rate than what is labeled will not increase control.

Additional Sources of Information:

Fact Sheet: Hemlock Woolly Adelgid, Penn State Extension

Fact Sheet: Elongate Hemlock Scale, Penn State Extension

Fact Sheet: Recommendations for Hemlock Woolly Adelgid Control in the Landscape, North Carolina State Cooperative Extension Service

Video: Hemlock Woolly Adelgid, Michigan State University Extension

Video: Invasive Species: Hemlock Woolly Adelgid - David Orwig, Harvard University

Reference:

Recommendations for Hemlock Woolly Adelgid Control in the Landscape, North Carolina State Cooperative Extension Service, by Dr. Jill R. Sidebottom, Area Extension Specialist and Christy Bredenkamp, Swain and Jackson Horticultural Agent, June 2009.

Establishing Streamside Forests: Bare Root, Container Grown, Live Stakes, and Direct Seeding

Over one third of the land in the Chesapeake Bay watershed is either covered by development or agriculture. This poses obstacles to water quality in the form of nutrients, sediments, and other pollutants, but also to terrestrial wildlife that have little or no habitat in these settings. Trees planted along city streets and in suburban backyards may feel like a sort of coexistence with nature, but in reality these manicured settings provide habitat for very few native species.

Farmland can also be deceptively “natural”; despite expansive hayfields and lush row crops, there are few places for wildlife to nest, raise young, or eat. Waist-high hay and six-foot-tall corn are eventually cut, leaving no cover for all but the smallest animals. Luckily, both water quality and wildlife habitat issues can be addressed with one management practice: establishing forest cover alongside streams and other water bodies.

Healthy streams and watersheds rely on functional riparian forest corridors. A streamside forest will trap and filter nutrients and sediment from the uplands that would otherwise flow into the stream. The overhanging tree canopy will cool down the water to make it suitable for trout and other native aquatic fauna.

They can also be important for terrestrial wildlife, especially in landscapes dominated by agriculture or development. Stream corridors composed of trees, dense shrubs/saplings, and native herbaceous vegetation provide breeding, foraging, and escape cover for an array of upland and lowland wildlife species that would otherwise have little to eat and no shelter from predators or the elements.

Establishing a streamside forest can be challenging as weather, deer, small mammals, and invasive plants all make tree survival and growth difficult. To learn more, come join the Rothrock Chapter of the Society of American Foresters as they host a summer field tour focused on riparian buffer establishment. The field session will take place on Thursday, June 22, 2017 from 2:00 PM - 5:00 PM along Muddy Creek just south of Spring Mills in Georges Valley, Centre County. The tour will access Muddy Creek off Harter Road. 

The afternoon will be spent visiting research sites along Muddy Creek to view riparian buffer establishment projects. Attendees will learn about tree establishment using bare root and container grown seedlings as well as live stakes and direct seeding. In addition, site preparation, weed suppression, invasive plant control, maintenance, and deer exclusion/protection will be covered in detail.

Pre-registration for the field tour is required. The field tour is provided free of charge. However, to better plan for attendance we are asking everyone to please pre-register by contacting the Penn State Extension office in Centre County by phone at: (814) 355-4897 or email CentreExt@psu.edu. Please register by Monday, June 19, 2017. Be sure to provide your contact information in case we have to get in touch with you.

Text provided by Ryan Davis, Chesapeake Forests Program Coordinator, Alliance for the Chesapeake Bay and Dave Jackson, Forestry Educator, Penn State Extension

Kiss your ash trees goodbye ... unless you treat now

Attention ash-tree owners: The day of reckoning is here. An imported wood-boring bug called the emerald ash borer has been wiping out ash trees over the eastern half of the United States, and it's now fully parked in Pennsylvania. The bug is poised to kill just about all of the 308 million ash trees in our forests, parks and neighborhoods.

"Our part of the state is definitely in the eye of the storm," says Dan Devlin, director of the state Department of Conservation and Natural Resources' Bureau of Forestry. "It's impacting us quite a bit. Drive around, and you'll see dead ash trees everywhere."

The borer's deadly work became painfully apparent here last summer and fall. Chainsaws were buzzing overtime, cutting down dead and mortally wounded ash trees in yards throughout the Harrisburg area. Jackie Kauffman lost two mature ones in her New Cumberland yard last September. "It's a real bummer, but we had no choice," she said, adding that neighbors on her street have cut down six others.

Ash trees with bark damage from woodpeckers

"Our Forest Hills neighborhood (near Linglestown) has been devastated by the emerald ash borer," says Dan Berman, a resident there. "I can drive down the streets and keenly point out ash trees that are just a season or two away from meeting the tree-trimming service."

The alarming part is that the emerald ash borer is so devastating that it's expected to kill nearly 100 percent of ash trees within four to five years. In other words, if you have one, it's almost a sure bet to die - unless you take action to protect it with regular applications of a chemical insecticides.

See Penn State Extension's tips on how to identify an ash tree.

The emerald ash borer is an Asian native that likely rode wooden packing materials to America. It was first discovered destroying ash trees in Michigan in 2002. Since then, it's moved mostly south and east by firewood and flight, killing tens of millions of all species of ash trees in 20 states. The first ones showed up in central Pennsylvania in 2012.

"It didn't take long to get from Michigan to here," says Devlin. "It takes four to five years to kill a tree. So by the time you see damage, the borer has been there several years. It jumped ahead of everybody." As spring unfolds, we're about to see this bug's peak performance.

Many municipalities, power companies and tree-owners already are cutting down ashes pre-emptively. It's too expensive to chemically protect masses of ash trees, and if you wait until they're failing, they became fall hazards and much more expensive to remove. (Brittle dead and dying ash trees are more hazardous for tree companies to work on than healthy, solid ones.)

Ash-bearing homeowners face a similar dilemma. Do you ignore the coming threat, figuring you'll pay later if necessary while hoping the tree doesn't fall down in the meantime? Do you bite the bullet and pay a few hundred dollars now to remove a tree that might look fine? Or do you invest hundreds or even thousands of dollars for unknown years of treatments to save your ash from the borers?

D-shaped exit hole

The most effective treatment is an insecticide called emamectin benzoate, which tree companies can inject into the trunk of ash trees every two years. Michael Dunn, an arborist for Bartlett Experts, says it's about 99 percent effective and is best applied in May or June. Imidacloprid is a less expensive and more readily available insecticide that homeowners can apply as a soil drench. But Dunn says it's only about 50 percent effective and has to be applied each year.

The key is that you can't wait until the tree is badly infested. Signs of trouble include dieback of branches; bark that turns light-colored ("blonding") and then starts splitting or sloughing off; a rush of new shoots sprouting from the trunk, and woodpeckers poking holes in an attempt to feast on the larvae inside. The telltale sign is D-shaped holes in the trunk and large branches. Those are holes made in May to early June by the newly matured adults exiting the tree to fly around and mate in summer.

See pictures of emerald ash borer and damage signs.

Adults look like elongated beetles - less than the size of a small paperclip - with shiny, dark-green shells,, hence the "emerald" in the bug's nickname.

See pictures of native borers and emerald ash borer look-alikes.

After mating, females lay eggs in bark cracks. The eggs hatch into larvae that look like fat, cream-colored, worm-like critters (larva) that feed on the wood inside, ruining the trees' ability to move water and nutrients up and down the phloem layer.

"Once a tree has emerald ash borers, the treatment recovery rate goes down exponentially," says Dunn. Adds Devlin: "People think they're catching it early when they're really not. If the tree is looking bad, it's probably hopeless already." He says chemical controls are more of an option for homeowners who have just one or a few trees that they don't want to lose. The decision boils down to how valuable the trees are and whether you're willing to spend the money to protect them.

"My recommendation is to get somebody in there who's an experienced professional," says Devlin. "One problem is that ash is brittle and breaks easily once it starts to fail... The rule of thumb is that if there's an infestation within 10 miles, and you don't have the borer yet, you might have a year before it shows up."

Some say you may not have to treat forever. If the borers move through like a tsunami wave and wipes out most ash trees, their populations could crash in 15 to 20 years when there aren't any/many ash trees left to eat. Others fear there will be enough floating around to always be a threat - or worse yet, that the bug will adapt to other species, such as related plants in the olive family. (The fringe tree is one example where a few emerald ash borers already have been found.)

See homeowners guide to emerald ash borer treatment.

Still others are putting their hope in the few ash trees - called "lingering ash" - that have managed to survive in the borers' wake. Penn State University, for example, has lost 95 percent of the ash trees that forest biologist Dr. Kim Steiner planted in a 2,100-tree experimental green-ash grove in 1975. Most of the rest are expected to die this year. "But we have about 15 trees remaining that show little to no dieback," says Steiner, now director of the Penn State Arboretum.

Those and others in Ohio are being studied for their borer-resistance with the hope that their genetics could be the base for a rejuvenated after-life. Ironically, ash was widely planted as a shady substitute for elm trees, which were nearly wiped off our botanical map due to the deadly Dutch elm disease in the 1960s. Disease-resistant elm trees are now being brought back after decades of back-crossing in which "lingering elms" played a key role. The poetic justice is that these new elms may now step back in as one of the possible replacements for ash.

See a dozen mid-size trees that make good replacements for a dead ash.

For more information on emerald ash borer from Penn State Extension click here. 

Reprinted from Penn Live

April 27, 2017

By  George Weigel