An Integrated Approach to Ambrosia Beetle Management in Ornamental Tree Nurseries: Biology of and Control Measures for Exotic Xyleborina

Ambrosia beetles have been a challenge to profitable nursery production for decades, with management recommendations focused on population monitoring and properly-timed insecticidal applications. Beetles disperse from forests starting in early spring, but few studies have determined the extent of this flight period, or how far they will fly into a nursery. And while the use of semiochemicals by ambrosia beetles has been widely examined, their use of visual cues including colors represents another gap in our knowledge. In addition to these under-studied behavioral traits, the available chemical control measures for ambrosia beetles are not completely effective, and repeated applications become costly for growers. Additional options are needed to reduce treatment frequency and to provide acceptable protection. The first experiment from 2012-13 determined beetle response to thirteen different trap colors. Mean beetle capture from opaque and red traps was significantly higher than from yellow or white traps, but we recommend that industry-standard black traps are adequate for ambrosia beetle monitoring. The second experiment from 2013-14 determined the timing of beetle flights and dispersal distance, as well as optimal trap and crop location. In addition to the well-documented spring flight, southeastern nursery managers need to be aware of a second, late-summer flight. Captures from traps placed at various distances (-25 to 200 m) from the forest/nursery interface showed a significant decreasing trend in numbers of beetles captured over increasing distance from the forest. Susceptible tree cultivars may gain added protection when placed deeper within nursery interiors and when baited traps line adjacent nursery edges. The third experiment from 2014-15 tested four treatments (kaolin clay, bifenthrin, kaolin + bifenthrin, and an untreated control) applied to ethanol-baited trees, with counts of new ambrosia beetle galleries compared roughly every other day for two weeks. While kaolin trees were better-protected than untreated trees at one day after treatment, subsequently there was no significant difference from untreated controls. And while there was a numerical reduction in attacks on kaolin + bifenthrin trees vs. bifenthrin trees, the effect was not statistically significant at any time