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effective pheromone traps for EAB. However, method were completely ineffective, even though tree size and infestation pressure occurs between 450-550 degree days (start-were very similar. It should be noted that ing date of January 1, base temperature of recent studies have shown that imidacloprid soil injections made at the base of the trunk bloom of black locust (Robinia pseudoacacia). result in more effective uptake than applica- For best results, consider two applications, tions made on grid or circular patterns under one at 500 DD (as black locust approaches the canopy. 50 full bloom) and a second spray four weeks Imidacloprid soil drenches have also gen- later. erated mixed results. In some studies conducted by MSU and OSU researchers, imidacloprid soil drenches have provided H excellent control of EAB. However, in other Insecticides for Control of studies, control has been inconsistent. Expe- EAB adults must feed rience and research indicate that imidacloprid EAB? on foliage before they soil drenches are most effective on smaller become reproduc- Extensive testing of insecticides for control trees and control of EAB on trees with a DBH tively mature. of EAB has been conducted by researchers that exceeds 15 inches is less consistent. at Michigan State University (MSU) and The This inconsistency may be due to the fact Ohio State University (OSU). Results of some that application rates for systemic insecticides of the MSU trials are available at www.emer- are based on amount of product per inch of aldashborer.info. trunk diameter or circumference. As the DBH of a tree increases, the amount of vascular Soil-Applied Systemic Insecticides tissue, leaf area and biomass that must be protected by the insecticide increases expo- - nentially. Consequently, for a particular appli- trolling EAB has been inconsistent; in some cation rate, the amount of insecticide applied trials EAB control was excellent, while others as a function of tree size is proportionally yielded poor results. Differences in applica- decreased as trunk diameter increases. tion protocols and conditions of the trials Hence, the DBH-based application rates that effectively protect relatively small trees can be too low to effectively protect large trees. . For example, an MSU Some systemic insecticide products address study found that low-volume soil injections of this issue by increasing the application rate imidacloprid applied to small trees averag- for large trees. ing 4 inches in DBH (diameter of the trunk at breast height) using the Kioritz applicator In an OSU study with larger trees (15- to (a hand-held device for making low-volume TM 22-inch DBH), Xytect (imidacloprid) soil injections) provided good control at one drenches provided consistent control of EAB site. However, control was poor at another when applied experimentally at twice the rate site where the same application protocols that was allowed at that time. Recently, the were used to treat larger trees (13-inch DBH). TM Xytect Imidacloprid levels may have been too low in of this higher rate, which we now recommend the larger trees to provide adequate control. when treating trees larger than 15-inch DBH. Higher pest pressure at the second site also ® Merit imidacloprid formulations, however, may have contributed to poor control in the are not labeled for application at this high large trees. rate. Therefore, when treating trees greater ® than 15-inch DBH with Merit soil treatments, In the same trials, high-pressure soil injections two applications are recommended, either of imidacloprid (applied in two concentric in the fall and again in the spring, or twice rings, with one at the base of the tree and the in the spring, about four weeks apart (for other halfway to the drip line of the canopy) example in late April and again in late May). provided excellent control at one site. At TM This is not an option for Bayer Advanced another site, however, soil injections applied Tree and Shrub Insect Control and other using the same rate, timing and application 8 INSECTICIDE OPTIONS FOR PROTECTING ASH TREES FROM EMEORER