Chemical Treatment

 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

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.

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