Treatments are most effective when a tree is actively carrying water and nutrients up through its system to the uppermost branches and leaves. Spring is best, but fall is effective, too. In drought conditions, trees must be watered heavily first.
• TREE-Age (Emamectin benzoate)
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Method: Injected into tree, can be done only by licensed technicians (which can include public works employees). Advocates say a tree heals between treatments because it is injected at most every other year, and the wounds are plugged.
Advantages: Considered the most effective treatment to date, and one treatment works for two or three years.
Costs: Ballpark is $100 per tree, although homeowners have banded together to negotiate deals. Price is usually based on the tree diameter -- one company says their charge varies from $7-$16 per diameter inch.
• Imidacloprid (out of copyright; available under several names)
Method: Homeowners can mix with water and drench ground around base of tree, or licensed technicians can inject into tree or soil. Must do annually to be effective.
Advantages: Do-it-yourself benefits.
Cost: Bayer brand suggested retail is $20 for 32 ounces; 1 ounce is needed for each inch circumference, measured where the tree is chest high.
Method: Homeowners can sprinkle dry around tree; product designed for commercial use can be sprayed to moisten the lowest 5 feet of tree trunk or injected into the soil. Must do annually.
Advantages: The only spray product available; it requires little equipment and does not put holes in the tree; sprinkling has do-it-yourself benefits.
Costs: Seven pounds, which treats at least 30-inches (diameter) of trees, are available online for $43 as Green Light Emerald Ash Borer Killer. However, Scotts is replacing this with a new product because Dinotefuran is coming off patent.