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Chemical Controls

Chemical controls, treatments that can be applied to infested trees to kill the adelgids, are the best option for property owners from the standpoint of both effectiveness and cost.  They fall into two general categories -- systemic and non-systemic materials.   They can be applied by soil injection, soil drench, foliar spray, basal trunk spray, as a tablet or a dry granule, and are appropriate for both ornamental landscape trees and woodland settings.

Note:  Key stands of hemlocks on public land (national forests, state parks, etc.) are being treated with carefully managed programs of chemical and/or biological controls.   For more information, please visit the Biological Controls page and the Hemlock Conservation Areas page.

Choosing Systemic or Non-Systemic Treatment

The first choice to make is whether to use a systemic or non-systemic type of treatment, and there are quite a few products to choose from in each category.  Be sure the product you select is labeled for treating adelgids.

■   Systemic materials are absorbed by the tree and transported upward into the plant where they are ingested by the target pest.  This type of treatment is highly effective on 95-99% of the pests as they ingest an ingredient that affects their nervous system and kills them.  It does not need to fall directly on the insects and provides a period of residual protection for the tree.  The two most frequently used systemic materials are Imidacloprid, sold under several trade names, for lightly to moderately infested hemlocks and Dinotefuran, sold as Safari 20SG and Transtect 70WSP, for heavily infested hemlocks and very large infested hemlocks (greater than 20 inches in trunk diameter at breast height) showing zero or minimal new growth.  Neither is a restricted use product but generally must be purchased through a specialty store (see Contacts page).  Systemic products are appropriate for trees of any size in either landscape or woodland settings.

■   Non-systemic materials kill adelgids on contact and must fall directly on all the adelgids to be effective.  This type of treatment works by physically smothering the insects, so it is effective only during the months that the adelgids are out of their egg sacs and exposed (April through mid-May or mid-June through September).  Non systemic materials provide no residual protection and must be repeated frequently.  Examples of non-systemic materials are horticultural oils or insecticidal soaps which can be purchased at most hardware stores.  Non-systemic products are appropriate only for hedges or small landscape trees of a size that the entire plant can be treated.

■   Note that in addition to the two primary treatment products mentioned above, there are other systemic and non-systemic Consumer Products that do-it-yourselfers may consider.

Selecting a Systemic Treatment Product

If the decision is made to use a systemic treatment, the choice of the most appropriate treatment product is based mainly on the level of HWA infestation, condition and size of the tree, soil moisture, and presence of spider mites and/or elongate hemlock scale.  See Photo Gallery for images of lightly, moderately, and heavily infested trees. 

Choosing between Imidacloprid and Dinotefuran

Here is advice from Mark Dalusky, UGA Forest Entomologist, on how to decide between Imidacloprid and Dinotefuran.  Click here for additional information and updates on choosing and using these products.

■   Cost -- Imidacloprid costs less than Dinotefuran.

■   Location -- If the tree is immediately adjacent to free water (streams, spring seeps, wet meadows), use Imidacloprid unless tree health is severely compromised; Dinotefuran can be used for heavily infested trees near water, but direct contact with water is prohibited.

■   Tree Health --

•         Use Imidacloprid on trees that are in reasonably good health (i.e., new growth and no significant needle loss). Use Dinotefuran on hemlocks where rapid control is required, i.e., trees with no new growth, badly thinning foliage, and dead or dying (usually lower) branches and especially on large diameter trees (> 20 inches DBH) with these symptoms.  Imidacloprid may still work but very slowly.

•         Remember that tree health determines how quickly and efficiently the hemlocks will mobilize the active ingredient to the sites of HWA feeding.

•         Imidacloprid can be effective on trees in advanced stages of decline, BUT you can expect tree health to deteriorate further before improvement is seen.  This may include loss of lower limbs. Do not expect to see new growth for about 2 years.  Survival of hemlocks is uncertain following Imidacloprid application if trees are in advanced stages of decline (gray foliage, >50% needle loss, dead lower limbs).

■   Presence of other pests -- Use Dinotefuran if scale or spider mites are a problem as treatment with Imidacloprid may intensify these conditions.  This decision is based on tolerance to their feeding symptoms.  These scale and mite infestations often self-resolve, especially in a forested setting, though not always. 

■   Timing -- In the southern Appalachians, Imidacloprid can be used any time of year when minimum soil moisture conditions exist.  Use Dinotefuran if you need to treat later in the season (late spring/summer) when conditions have become relatively dry.  Treatment during official drought conditions is not recommended; soil applications should not be done when the ground is saturated or frozen.

Imidacloprid (click here for product labels and MSDS)

Lightly to moderately infested trees can be treated effectively with a 75% water soluble formulation (WSP or WSB) of Imidacloprid. 

Imidacloprid poses minimal risk to man and the environment when used according to the label.  Research studies have shown only 6-12” of movement in the soil from the injection points.
 

■   Ease of Use -- Easy to calculate mixing proportions and to apply.

■   How Applied -- Imidacloprid 75 WSP/WSB can be applied by soil injection, soil drench, or foliar spray.  Soil injection is recommended for best results because it delivers the treatment directly to the root level.

•         Soil condition:  Do not inject into saturated or frozen soils, shallow soils over rock, or extremely sandy soils particularly those lacking organic matter.  Soils that puddle in your footsteps or from which you can squeeze free water out of a handful are too wet.  Soil that clumps at all with hand pressure is OK.

•         Injection depth:  Depth of injection is critical for effective treatment!  Set injection depth in the 2-5 inch range. The majority of the feeder roots are within 6 inches of the soil surface.  Deeper roots are mainly for water acquisition and anchorage.  Leaf, twig and limb litter on the surface should be accounted for when calculating injection depth.  If substantial, it may need to be pushed aside temporarily.  Injecting too deep is inefficient and risks contaminating groundwater.

•        Injection placement:  The majority of the feeder roots are within 2 feet of the trunk.  Injecting in this zone is most efficient, but if necessary, soil injections can be effective when placed within the drip line of the tree.  This can be useful for protecting trees that are located close to streams.

■   Timing of Treatment -- Initially, the recommendation for time of year to inject was either in the spring or late fall.  Now, as mentioned earlier, in the southern Appalachians we recommend using Imidacloprid any time of year when minimum soil water conditions exist.  Evapo-transpiration occurs year round in the South with peaks in the spring and fall.  It is adequate to mobilize active ingredient in all but moderate to severe drought conditions. Research at UGA indicates that you can even inject into a very droughty soil and expect the active ingredient to still be effective up to 2 full years later when soil water conditions improve.  Apparently, with proper injection technique, Imidacloprid is well protected in the organic layer and will persist for several years under extreme drought conditions.  That said, the optimum time of year for soil injection is still October through mid-June.  This optimal period can be extended by good rains in June, and rains beginning earlier in September; but if time is the limiting factor, then the summer treatment option exists.  Treatment should not be done during rainfall or within 12 hours before or after rain.

■   Speed of Action -- Time to reach full strength in the tree depends on the tree's size/diameter.   It can take from 6 weeks to 12 months or longer to become effective.  It might take several years to achieve complete control and show new growth, particularly in large diameter trees.

■   Residual Protection -- In the South, it remains effective for an average of 3 - 5 years before retreatment is necessary.  Hemlocks should be examined for presence of HWA prior to retreatment as reinfestation by HWA might take several years.

■   Cost -- This material is sold under several trade names and package sizes, but ask for a generic version of the product in 1.6 oz packaging of 75% WSP (water soluble powder) labeled for treating adelgids.  A four-pack typically costs between $35 and $50.  Using the do-it-yourself option and assuming a cost of $50 per four-pack, treatment cost ranges from $.17 to $.52 per diameter inch, and compared to an average of $1.50 - $4.00 per diameter inch for professional treatment.  The Hemlock Help Line^SM can assist you in finding the most appropriate product and source.

Merit 75% WSP is Bayer's original Imidacloprid product for HWA.  The generic formulations are chemically equivalent, equally effective, and less expensive.  The following is a partial list of generics, provided for information purposes only, not as product recommendations.  Places that sell these and other HWA treatment products are listed on the Contacts page.

Dinotefuran (click here for product labels and MSDS)

Hemlock that are heavily infested and very large infested hemlocks (greater than 20 inches DBH) showing zero or minimal new growth require a more rapid-acting product containing Dinotefuran, sold as Safari and Transtect.  (It's also good for hemlocks that are heavily infested with elongate hemlock scale or spider mites.)  Safari is available as a 20% concentration soluble granule (SG) that is mixed in water or a 2% granule that is applied dry to the soil; Transtect is available as a 70% concentration water soluble powder (WSP). 

Dinotefuran poses minimal risk to man and the environment when used according to the label.  Due to its chemical properties, Dinotefuran is taken up more quickly by hemlocks and provides faster control of adelgids than Imidacloprid.  Dinotefuran is labeled for application to hemlocks in ornamental landscapes and forests. 
 

■   Ease of Use -- About the same as Imidacloprid to calculate mixing proportions and apply; a sprayer is needed for basal trunk spray method.

■   How Applied -- Dinotefuran can be applied by a foliar spray, soil injection, soil drench, or basal trunk spray.  The basal trunk spray application technique is useful for wet or difficult sites (underlying rock, deep sand etc.) or for trees located close to waterways; this technique is now in use and particularly effective for late spring or summer treatments. 

•         Soil condition:  Dinotefuran is more effective than Imidacloprid in dry soils.

•         Injection depth and placement:  Soil injection requirements are similar to Imidacloprid.

■   Timing of Treatment -- If Dinotefuran is used for soil application, the timing recommendations are the same as for Imidacloprid.  The manufacturer recommends that Safari 20 SG be applied from February 1 to November 15 when hemlocks are actively taking up water from soil.  If Dinotefuran is trunk-sprayed, do not apply to wet bark, during rainfall, or if rain is expected within 12 hours.  Don’t apply during extremely dry periods.

■   Speed of Action -- Dinotefuran can reach lethal concentrations in foliage in as few as 3 weeks (usually 4-6), and control of adelgids is usually observed within 2-6 weeks after application, depending on tree size and health.

■   Residual Protection -- Reapplication is within 2 years, depending on reinfestation pressure in the area.

■   Cost -- Safari 20 SG is sold in a 3-pound container, costs $350 - $400, and treats up to 408 inches of trunk diameter at the lowest dosing rate; it is also now available in a 12-ounce size.  Transtect 70 WSP is sold in a canister containing twenty .6-ounce water soluble packets, costs about $340, and treats up to 340 inches at the lowest dosing rate.  Using the do-it-your self option and assuming a cost of $350 for a  container or canister, treatment cost ranges from $.77 to $3.07 per diameter inch, compared to an average of $3.00 - $9.00 per diameter inch for professional treatment.

Choosing an Application Method

The choice of application method is based on the size and condition of the tree, treatment product being used, and location of the tree relative to sensitive areas.  Here are some general guidelines, but always follow the product label.

NOTE:  Trunk/stem injection is another possible application method, but many experts recommend AGAINST it.  This method is extremely expensive, requires great skill to do properly, fails to work successfully up to 40% of the time (according to the U.S. Forest Service), and can actually damage the tree.  In the rare cases where it may be appropriate, it should be done by a highly experienced, licensed professional.

Advantages of Chemical Controls

While it may not be possible to save every hemlock, in most cases chemical controls are highly effective in killing 95-99% of the adelgids and providing a period of residual protection.  In addition, they can be applied economically by property owners following the product labels or by licensed professionals such as those listed on the Contacts page of this web site.  There is no charge for borrowing a soil injector, only a refundable deposit.

Disadvantages of Chemical Controls

There is some cost involved to purchase the treatment products as well as some physical work for property owners who choose the do-it-yourself option; or there is the cost of hiring a professional.  And while chemicals can provide excellent results, they are still only a temporary measure until a long-term solution is developed.

Special Notes

■   Pesticides used improperly can be injurious to humans, animals, and plants.  Follow the directions and heed all precautions on the labels.  Don't use too much or too little.  Click here for access to Product Labels and MSDS (Material Safety Data Sheets) for the products mentioned above. 

■   Visible signs of improvement in treated trees include a reduction in the number and coverage of egg sacs, no or fewer egg sacs the following egg-laying season, new growth the following spring, better foliage color and density, and overall improved vigor of the tree.  In trees treated with Dinotefuran, these signs are usually observable within the first 3 months after treatment.  However, in trees treated with Imidacloprid, the property owner should be advised to be patient as improvement may not be observable until 6 to 18 months after treatment, depending on tree size and the health of the tree at the time of application.

■   Sometimes, one tree doesn’t take up the chemical as well or quickly as its neighbors, doesn’t show the normally expected improvement, and must be re-treated the following season or year to bring the chemical effectiveness up to the required level.  No matter which product is used, homeowners should be advised to keep a watchful eye on their treated hemlocks to identify any that may not be responding as well as desired.

■   Chemical controls can and should be used in combination with cultural controls. 

■   For detailed information on the safety of using Imidacloprid near waterways, click here to review Jim Hanula's presentation to the HWA Symposium held in Dahlonega in February 2009.  For information on the safety of using Imidacloprid around honeybees, click here for an information statement.

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© Save Georgia's Hemlocks 2009.  Last updated 01/18/2012.
Send comments or questions to donna@savegeorgiashemlocks.org or call the Hemlock Help Line^SM  706-429-8010.