About Us
Hemlock Message
HWA Controls
Hemlock Help
Contacts & Sources
How You Can Help
Schedule of Events
Site Map


Next Leadership 
Team Meeting

Sunday, Apr. 14

starting at 1 p.m.

Chemical Treatment

NOTE:  The information provided here is based on product labels and advice from experts,
including various public land managers, product representatives, and the University of Georgia.
It is the user's responsibility to read and follow the label instructions when using pesticide treatments

 Choosing Systemic or Non-systemic Treatment       Selecting a Systemic Treatment Product       Imidacloprid       Dinotefuran        Consumer Products      
 Choosing an Application Method
      Advantages of Chemical Control        Disadvantages of Chemical Control        Special Notes

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 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 for lightly to moderately infested hemlocks and Dinotefuran 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 or web site (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 insecticide 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

See the Contacts page for sources to purchase products.

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

   Cost -- Imidacloprid costs significantly less than Dinotefuran on a per-diameter-inch basis.

   Location -- For trees immediately adjacent to free water (streams, spring seeps, wet meadows, drainage areas), use Imidacloprid unless tree health is severely compromised.  If using Imidacloprid on a tree with less than 3 feet between the trunk and the water, apply the full dosage on the side away from the water.  If using Dinotefuran on a severely infested tree with less than 3 feet between the trunk and the water, either apply the full dosage on the side away from the water or use the basal trunk spray method.  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 efficiently a hemlock can mobilize the active ingredient to the sites of HWA feeding.

•         Imidacloprid can sometimes be effective on trees in advanced stages of decline, BUT you can expect tree health to decline further before improvement is seen.  This may include loss of lower limbs. Do not expect to see new growth on such trees 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 the tree owner's tolerance to the pest's feeding symptoms.  Scale and mite infestations often self-resolve, especially in a forested setting, though not always. 

   Timing -- Keeping in mind that the best time to treat a hemlock is yesterday and the next best time is as soon as possible, here is some general advice concerning timing.  Then see the sections that follow for choosing Imidacloprid or Safari. 

•         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.

•         Treatment during official drought conditions is generally not recommended; soil applications should not be done when the ground is saturated or frozen.

•         Treatment should not be done during rainfall or within 12 hours before or after rain.

Imidacloprid -- click here for product labels and SDS (safety data sheets)

Lightly to moderately infested trees can be treated effectively with Imidacloprid in any of three formulations:  powder 75 WSP or WSB ,liquid  Imidacloprid 2F or 2L or 4F, or dry tablets called CoreTect.

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 or insertion points.

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

   How Applied -- Imidacloprid is labeled for soil injection, soil drench, or tablet insertion.  It's also labeled for foliar spray, but we don't recommend this method in general. 

•         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 with hand pressure is OK.

•         Injection depth:  Depth of injection is critical for effective treatment!  In most cases, set injection depth in the 4-6 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.  Note that seedlings and small saplings will have a very shallow feeder root zone at just 2-3 inches below the surface.  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.

•        Injection placement:  The majority of the feeder roots are in a dense mat just under the trunk.  Injecting within 1 foot of the trunk is most efficient, but if necessary, soil injections can be effective when placed farther out but still within the drip line of the tree.  This can be useful for protecting trees that are located immediately next to a stream.

   Timing of Treatment -- In general, the best time to treat hemlocks is the present moment.  Imidacloprid can be used any time of year when minimum soil moisture conditions exist.  That said, the optimal times of year for soil injection are spring and fall.  

   Speed of Action -- Time for Imidacloprid to reach full distribution and strength in the tree depends on the tree's original health, diameter, and growing site.   In general, healthier trees will respond more quickly than sicker ones.  Full distribution of the treatment occurs soonerin small trees than in larger ones.  And trees growing in sunny conditions are able to draw up the treatment materials more efficiently than those growing in shady sites.

•         Small trees up to 4 inches in diameter can have full distribution of the treatment from 6 weeks to 6 months.

•         For medium trees 4 to 18 inches in diameter the time frame is usually 6 months to a year.

•         For trees larger than 18 inches full distribution can take up to 18 months.

•         And trees larger than 22 inches should be treated two consecutive years to get the full 5 years of protection.

•         Improvement usually can be observed the spring following application, but it might take several years to achieve complete control and show new growth, particularly in large diameter trees.

   Residual Protection -- In the South, Imidacloprid remains effective in the tree for an average of 5 - 6 years before retreatment is necessary;  however, hemlocks should be examined for presence of HWA prior to retreatment as reinfestation may occur sooner or later than the average.

   Cost -- Bayer products are the original brand name version of Imidacloprid; however. generic products are chemically equivalent, equally effective, and generally less expensive.   Of the three formulations, the liquid is the most economical on a per-diameter-inch basis. 

•         A four-pack of Imidacloprid 75 WSP typically costs about $35 and treats an average of 181 diameter inches.

•         A gallon of Imidacloprid 2F or 2L typically costs $75 - $95 and treats an average of 1,208 diameter inches.

•         A bottle of 250 CoreTect tablets typically costs about $113.

•         If you want to treat your own trees, the Hemlock Help Line 706-429-8010 can assist you in finding the most appropriate product and source.

Below 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.


Generic Powdered Formulations of Imidacloprid 75% WSP / WSB

 Bandit 75% WSP

 Criterion 75% WSP

 Enforce 75% WSP
 Hunter 75% WSP

 Imida-E-Pro 75% WSP

 Mallet 75% WSP

 Malice 75% WSP

 QualiPro 75% WSB

 Submerge 75% WSP

 TouchStone 75% WSP

 XyTect 75% WSP

 Zenith 75% WSP

Minimum quantity for purchase  is one four-pack.

Each four-pack contains 4 packets of 1.6 oz. each and treats an average total of 181 diameter inches.

A case contains 4 four-packs with a total of 544 grams of active ingredient and treats an average total of 724 diameter inches.


There are several generic liquid/flowable Imidacloprid products that are even more economical than the generic powders for large treatment projects.  The 2F and 2L formulations listed below are flowable or liquid products and usually sold by the gallon.  Don’t let the 21.4% or 22.6% strength mislead you. Each gallon contains 2 full pounds of the active ingredient and, when mixed with the proper amount of water, yields the same concentration of active ingredient per ounce of mixture as the powdered products.   And since it's a liquid, it mixes more readily than the powder and tends not to fall out of suspension and clog an injector as quickly.  

Generic Liquid Formulations of Imidacloprid 2F / 2L

Amtide 2F T&O 22.6%

Criterion 2F 21.4%

Dominion 2L 21.4%

Garant 2F T&O 21.4%

Hunter 2F 21.4%

ImidiPro 2F 21.4%

Lada 2F 21.4%

 Lesco Bandit 2F 21.4%

Quali-Pro 2F 21.4%

Submerge 2F 21.4%

Touchstone 2F 21.4%

Widow 2F 21.4%

Xytect 2F 21.4%

Zenith 2F 21.4%

Each of these products is a flowable/liquid formulation that is sold by the gallon.  A few are also available in larger or smaller quantities. 

A gallon of the 2F or 2L products generally costs the same as a case of generic 75% WSP but contains more than 1 1/2 times the amount of active ingredient (2 pounds or 907 grams), so it goes much farther.  

A gallon of the 2F/2L products treats an average of 1,208 diameter inches. 

Mixing and dosing instructions for Imidacloprid products are included in the Treatment Instructions section on the Resources page.  Click here for their product labels and SDS.


Dinotefuran -- click here for product labels and SDS

Hemlocks 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, Transtect, and Zylam Liquid.  (It's also a better choice than Imidacloprid for hemlocks that are heavily infested with elongate hemlock scale or spider mites.)  The recommended formulation of Safari for treating hemlocks is the 20% concentration soluble granule (SG); Transtect is a 70% concentration water soluble powder (WSP); and Zylam is a 10% concentration liquid.  All three are designed to be mixed with water, preferably very warm water.

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, but its residual protection period is shorter.  Dinotefuran is labeled for application to hemlocks in both 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 is labeled for soil injection, soil drench, and basal trunk spray.  It's also labeled for foliar spray, but we don't recommend this method because of the risk of wind drift.  The basal trunk spray application technique is useful for wet or difficult sites (underlying rock, deep sand etc.)  This technique is particularly effective for late spring/summer treatments and for trees located close to waterways or where the root zone cannot be accessed. 

•         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 -- The most active period for Dinotefuran is 3 to 8 weeks following application.  Therefore, manufacturer recommends that Dinotefuran be applied between February 1 to November 15 to synchronize the most active time of the chemical with the period when the hemlocks are most actively taking up water and nutrients from the soil.  Dinotefuran may be preferable when conditions have become relatively dry, but it is not recommended for use during extremely dry periods.  If Dinotefuran is used for soil application, the timing recommendations are the same as for Imidacloprid.  If Dinotefuran is trunk-sprayed, do not apply it to wet bark, during rainfall, or if rain is expected within 12 hours. 

   Speed of Action -- Dinotefuran can reach lethal concentrations in foliage in as few as 3 weeks (usually 4-8 weeks), and control of adelgids usually can be observed within 2-6 months after application, depending on tree size and original health.

   Residual Protection -- Reapplication is within 2 years, depending on reinfestation pressure in the area.  However, unless the root zone is inaccessible or there is some other reason not to use soil application, once Dinotefuran has been used to save the life of a tree, it is usually possible to switch over to a five-year treatment cycle of Imidacloprid.

   Cost -- Safari 20 SG is sold in a 3-pound container, costs about $400, and treats an average of 283 diameter inches; it is also available in a 12-ounce size costing about $120.  Transtect 70 WSP is sold in a canister containing twenty 0.6-ounce water soluble packets, costs about $470, and treats an average of 247 diameter inches.  If you treat your own trees, the only cost is the chemical itself.  Sadly, there is no generic version available at this time.

Places that sell these and other HWA treatment products are listed on the Contacts page.  Mixing and dosing instructions for Dinotefuran products are included in the Treatment Instructions section on the Resources page.  Click here for their product labels and SDS.


Consumer Products

The products listed below are considered consumer-grade products as they either contain a lower concentration of the primary active ingredients (Imidacloprid and Dinotefuran) or contain different chemicals.  They are generally available at hardware and big box stores.

Consumer Products

Advanced Tree & Shrub Protect & Feed liquid [Bayer] 

Advanced Trees & Shrub Insect Control granules [Bayer]

Coretect tablets [Bayer]

Greenlight Tree & Shrub Insect Control with Safari 20 SG granules [Valent]

Safari 2G granules [Valent]

Menace Flowable Insecticide [NuFarm]

Qualipro Insecticide/Miticide [FarmSaver]

Speckoz Termiticide/Insecticide [Speckoz]

Talstar liquid [FMC Corporation]

Imidacloprid 0.74%

Imidacloprid 2.9%

Imidacloprid 20%

Dinotefuran 2%
Dinotefuran 2%

Bifenthrin 7.9%

Bifenthrin 7.9%

Bifenthrin 7.9%

Bifenthrin 7.9%

Soil treatment

Soil treatment

Soil treatment

Soil treatment

Soil treatment

Foliar spray
Foliar spray

Foliar spray

Foliar spray

There are also insecticidal soaps and horticultural oils made by manufacturers such as Arysta, Biotech Solutions, Bonide, Espoma, Drexel, Fertilome Solutions, Natural Guard, Neudorff, Ortho, Pharm Solutions, Safer, Schultz, Spectrum, Wetsel, and Woodstream.  However, such products are topical rather than systemic, must fall directly on the insects to kill them, offer no residual protection period, and must be repeated frequently to maintain control.


Choosing an Application Method

See the Resources page for application instructions.

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.

 Soil Injection

Recommended for most conditions because it delivers the treatment material directly to the root system.  Use in soil with good organic content, clay or loam; may be used within a few feet of a sensitive area except where soil is mostly sand or gravel or is saturated.  To ensure getting the material into the root zone, remove surface leaf litter, expose bare soil, and make one injection hole per inch of trunk diameter 2" to 6" deep (depending on tree size) within 12" of the base, evenly distributed around the tree.  To facilitate ease of injection and quicker uptake during dry periods, watering the soil 6 hours before and 12 hours after treatment will help.

 Soil Drench

Appropriate for a few trees of any size growing in level or gently sloping ground.  To minimize run-off, remove surface leaf litter to expose bare soil, and use a hammer and rebar to make small individual holes, one per inch of trunk diameter, 2" to 6" deep (depending on tree size)  within 12" of the base, evenly distributed around the tree.  Pour treatment material gently into the holes, press holes shut, and replace the leaf litter.  Keep pets and children away from area until soil surface is dry.

 Foliar Spray

Apply ONLY on a calm day to avoid wind drift.  Use in early morning or evening to avoid sun-scorch of the needles or harm to beneficial insects during the day. 

Appropriate for small trees and hedges where all parts of the tree can be reached.  Systemic materials can be used pretty much year-round.  Insecticidal soaps are best used in warm weather from April through mid-May or July through September when the insect does not have its protective white woolly covering and the product can fall directly on the exposed adelgids.  Don't use horticultural oil from mid-May through late September as you may risk burning the plant in hot weather and suffocating the new growth.  Be sure to spray stems and undersides of branches as well as top sides.  Also helpful to use on the lower branches of badly infested trees that are being treated by soil application.  Use goggles and mask.  Keep pets and children away until material is dry.

 Tablet Insertion

Appropriate for sites where trees are growing right on a stream bank and leaching of liquid material could be possible, sites where treatment material must be carried on a waterway, or sites that are too remote to access or carry water for mixing chemical.   To ensure getting the material into the root zone, remove surface leaf litter, expose bare soil, and make one injection hole per inch of trunk diameter 2" to 6" deep (depending on tree size) within 12" of the base, evenly distributed around the tree.  Use gloves to handle tablets.

 Basal Trunk Spray

Apply ONLY on a calm day to avoid wind drift

Appropriate for heavily infested hemlocks, very large infested hemlocks, or in areas where soil application is not desired.  OK for Dinotefuran only, not for Imidacloprid.  Spray the trunk from 6 inches to 5.5 feet above the ground.  Do not allow material to drip down the trunk into the soil or enter a waterway.  Use goggles, gloves, and mask.  Keep pets and children away until material is dry.

NOTE:  Trunk/stem injection is another possible application method, but many experts recommend AGAINST it.  This method is extremely expensive, requires special equipment and great skill to do properly, fails to work successfully up to 40% of the time, and can actually damage a hemlock.  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.

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 SDS (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 may be observable as soon as the first 3 months after treatment but for sure the following spring.  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 practices

   For detailed information on the safety of using Imidacloprid near waterways, click on the link 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 (updated 5/4/15), click here for an information statement.

 Back to HWA Controls       Cultural Practices       Biological Controls


  Please LIKE US on Facebook.

© Save Georgia's Hemlocks 2009-2024. 
Send comments or questions by e-mail  or call the Hemlock Help LineSM  706-429-8010.