How Do I Save My Hemlocks

(Written by Mark Warren)

Problem and hope: In 2002 the Hemlock Woolly Adelgid arrived in Georgia along the Chattooga River, and now it is fast spreading through both the Etowah and Chestatee watersheds. (Infested Lumpkin areas include Yahoola, Two Run and Nimblewill Creeks.) We were told by scientists to expect in one decade the loss of 90% of our hemlock trees. As an individual landowner, you can change that prophecy for your hemlocks. You can save them. This article will tell you how.

Meanwhile more hope lies in the research being done: raising and releasing of adelgid-eating beetles; cross-breeding the eastern hemlock with adelgid-resistant hemlocks of the western U.S. and Orient; and finding adelgid-killing fungi.

In New Jersey and Connecticut, studies on public lands show a remarkable comeback by ravaged hemlocks in just a few years after the release of adelgid-eating beetles.

Why save my hemlocks? 1.) The efforts of the U.S. Forest Service and Georgia Department of Natural Resources will only address trees growing inside public (non-private) lands and only a small percentage of those. 2.) Of all the Georgia acres containing hemlocks, over 75% are privately owned. As majority owners, we - the private landowners - stand to lose the most - or contribute most to saving the species, which is at risk. 3.) The deep shade provided by stream-side hemlocks ensures the crucial cool temperature (for high oxygen content) necessary for aquatic life. With the hemlocks gone, certain aquatic species might be critically affected. Would trout populations suffer? We don't know. Perhaps. 4.) As far as aesthetics: Does a mental picture of your favorite spot in the mountains include hemlock trees?

Understanding the adelgid

When is my hemlock tree under attack? It begins non-dramatically. A few white fuzzy specks show up at the bases of needles. Each mass (with hundreds of eggs) is the size of a pin head or slightly larger. Once the aphid-like adelgid infests a tree, it reproduces quickly - running through two generations in one year. Within two to four years the tree is dead - a bare woody bone picked clean.

How did the adelgid find its way to my hemlocks? Since it is virtually immobile, it hitchhikes on wind, birds, cars, machinery and humans. A fisherman brushing past an infested bough in another county might bring the problem back to his favorite local fishing hole.

What can be done about the adelgid problem?

To date there are three approaches for treatment:

  1. Insecticidal soap sprays and horticultural oils applied topically.
  2. Pesticide injected into either soil or tree trunk.
  3. Biological control using predatory beetles.

What is being done about the adelgid problem? Utilizing the above methods, the United States Forest Service and the Georgia Department of Natural Resources have begun a counterattack to preserve individual trees or small stands of hemlocks scattered throughout public lands. Their goal is not to save as many trees as possible but to ensure the survival of the species for the sake of bio-diversity.

Private landowners are successfully halting the adelgid problem in their trees by hiring arborists or landscapers to implement the insecticidal or chemical options listed above. Some individuals have taken the initiative to do the work themselves - getting certified for pesticide application (for options 4 and 5 below), buying the chemical and applicator and working directly with infested trees.

I have hemlocks on my property. What are my options?If the adelgid is not already evident on your trees, you are advised to do nothing. The following options apply to infested trees:

  1. Do nothing - Be prepared to lose your trees as early as 2 years after infestation begins. Because resident hemlocks increase property value and because of the cost of removing dead trees, this option is not appealing.
  2. Spray with insecticidal soap or horticultural oil - Spray small trees, whose every branch can be reached. Repeat in spring or fall if the adelgid is still visible. Look for these soaps and oils at landscaping businesses, garden centers and nurseries. Because the product is diluted in water, allowing a little to go a long way, the cost is reasonable. (See Application Warnings below.)
  3. Soil drenching with imidacloprid - This treatment is for trees not growing close to a stream or wetland and involves pouring a prescribed concentration and quantity (as instructed on the label according to tree size) of a nicotine-related chemical (imidacloprid) around the base of the tree inside a shallow trench and small earthen berm. Repeat if infestation recurs (likely between 2-4 years) until the adelgid is no longer evident. Apply only in early spring or early fall (cool weather) when the hemlocks are actively taking up water through their roots. If the soil is dry beneath the tree, thoroughly water it before application so that the tree can absorb the chemical. Further dampening will be required for two weeks if rain does not accommodate. One imidacloprid product (Bayer Advanced) is available to the public at landscaping businesses, garden centers and nurseries. The use of certain brands ("restricted use" pesticides are so labeled) requires the user to have a certified pesticide application license. A homeowner can get a license if actively producing an agricultural commodity and if willing to study and then pass a series of tests. One local certified and licensed applier is Mark Shearer (706-864-4787, markshearer@windstream.net). (See Application Warnings below.)
  4. Soil injection with imidacloprid - This technique delivers by pressure through a specialized injector (one brand is Kioritz) 6 inches or less underground. This subterranean application appears to be the safest and most effective technique, showing a higher mortality rate for adelgids. As in soil drenching, do not use the chemical near streams or wetlands. Apply only in early spring or early fall. Application is probably needed every 2-4 years. Use the same dampening preparation and follow-up as mentioned above in option 3. The cost of an injector runs about $350. Neighboring stewards might consider buying the tool for joint use, but the applier must be licensed. Depending on the number of trees to be treated, consider the cost effectiveness of hiring a professional. Some arborists charge about $12 to $25 per injection. The number of injections depends upon tree size. (See above paragraph for name of certified applier.) (See Application Warnings below.)
  5. Stem (trunk) injection with imidacloprid - This application is typically reserved for sensitive areas: trees near surface water or saturated soil or located on rocky or sandy soil. A low-pressure stem injector is needed; and because of the specialized chemical and equipment needed for this procedure, professionals should be hired to inject. Stem injection is more expensive - costing from $12 to $25 per injection and the number of injections depending upon tree size. One company charges $15 X inches of trunk diameter at breast height. Though not as effective as soil injection, it is the necessary option for special-case trees. No homeowner brands of pesticide for this application are sold. A certified and licensed applier must be used. (See Application Warnings below.)
    • Signs of success with imidacloprid. Soil treatments and stem injections may take several months to produce visible results. The tree's health and the weather are factors that cause significant variations in the time it takes a tree to absorb the chemical and distribute it to the branch ends. As the adelgids die, their white wool turns gray and starts to disintegrate, and in subsequent seasons, less wool will be observed. If you don't see good results on the lowest branches, don't be overly concerned. Hemlocks "prioritize" their upper branches; therefore the chemicals will not be distributed as well to lower branches.
  6. Release of predatory beetles on infested trees - At the time of this writing, sources for beetles to be purchased by the private sector are not abundant. In North Carolina, Conservation Concepts (www.conservationconcepts.org, P.O. Box 937, Old Fort, NC 28762, 1-828-221-2142) sells a minimum of 1000 beetles at $2.29/beetle. Ecoscientific Solutions (www.ecoscientificsolutions.com, 930 Meadow Ave. Ste. 2B, Scranton, PA, 18505, 1-888-ECOSOLV) is another source. More labs will undoubtedly become established and some of these will cater to the public. Opinions differ on how many beetles should be released on an individual tree, 15, 50, 100 or some other number? This number hinges on the beetles' propagation success in the wild. But releasing a relatively small number of beetles (say a few hundred) in one area will probably not deliver a desired effect. Better results would come from landowners pooling their resources to purchase and release thousands of beetles. The realistic goal of the landowner should not be to completely eliminate the adelgid but to create a balance of predator and prey as exists in the Orient, where hemlocks are not dying. One newly studied species is showing an affinity for Georgia's weather and promises to be even more effective than other species.

What is my first step?

Consult a hemlock-savvy arborist, county agent or qualified landscaping specialist. Then make a realistic management plan that fits your budget. Decide how many and which trees you will save and which you will remove to maintain a healthy forest. As you ponder your options, consider protecting those very tall male trees that reach above the general canopy of the forest, as they are contributors of widespread-traveling pollen that can benefit other trees that might survive farther out in the forest. But give particular priority to female trees (with cones), which produce many hundreds of seedlings.

What application warnings should I be aware of?

  1. Do not begin any treatment at all until your trees are infested.
  2. Spraying tall mature trees results in pesticide "drift" outside your target area. Consider other options. If spraying small trees, do not allow drift or drip into nearby surface waters. Do not spray during the heat of summer as this can "burn" the needles.
  3. Imidacloprid is highly toxic. Although drenching is the cheapest method of application, there is risk concerning the environment. Researchers fear that a misuse of the chemical would eradicate large numbers of invertebrates in a contaminated area - especially aquatic life - thereby upsetting the food pyramid. If using a brand made for homeowners, carefully follow all label directions and warnings. For "restricted-use" brands, hire a licensed applier.
  4. The soil type where an infested hemlock lives might not be compatible with imidacloprid use. Dark, rich soil and clay are good compositions for use of imidacloprid, but rocky or sandy or swampy soils are not. Imidacloprid must be applied to an infected tree in early April or early October only; otherwise, time and money and effort might be wasted. If adelgids are detected in June, exercise patience and wait until fall to treat the tree.
  5. Trunk injection does deliver trauma to a tree, especially when repeated every few years. This method should be considered for "special case" trees where other treatment options are not feasible.
  6. Beetles (the good guys) die when they eat adelgids containing imidacloprid. Do not use both chemical and biological control in the same area. Beetles must be released not on solitary trees but on 15-50 infested trees in the same hemlock grove, where colonies can be established; otherwise, the beetles will have nothing to eat and nowhere to migrate after egg-laying (to leave their offspring the nearest available food). Trees need to be monitored to determine when and if additional beetles should be released.

To further educate yourself about the hemlock woolly adelgid problem and solutions, visit www.na.fs.fed.us/fhp/hwa/ on the Internet. To further the preservation of the hemlock trees, support the efforts of Lumpkin Coalition (www.lumpkincoalition.org) by attending:

Hemlockfest on Nov. 3 and 4 at Starbridge on Highway 52 east of Dahlonega.