Location: Application Technology Research Unit
2013 Annual Report
Collaborative research with ARS scientists was conducted into: (1) determining the effects of stress factors on woody ornamental susceptibility to ambrosia beetle attack, (2) characterizing the interactions between ambrosia beetle seasonal incidence, plant stress factors, environmental and phenological parameters in relation to ambrosia beetle attacks, and (3) screening insecticide and repellent biopesticides after ‘stress factors’ that predispose trees to attack have been identified. The following is a summary of research highlights from the five year project.
Tree attacks in Tennessee were mainly dominated by the granulate ambrosia beetle (Xylosandrus crassiusculus), the camphor shot borer (Cnestus mutilatus), and the black stem borer (Xylosandrus germanus).
Unlike results from North Carolina, Ohio, and Virginia, X. crassiusculus, X. germanus, and other ambrosia beetles did not selectively attack trees in Tennessee subjected to flood-stress and/or drought-stress. Ambrosia beetles in Tennessee also did not selectively attack trees subjected to defoliation, planting depth, and delayed dormancy. However, delayed dormancy appeared to have predisposed trees to attack.
Examinations associated with a commercial nursery that sustained extensive attacks on containerized dogwoods found the core bark zone from the original container was too dry, even though the surrounding bark mix in the bump up container was damp. The potting mix also had almost no air space, which may have led to the roots being starved for oxygen. Ethanol is often produced by a number of tree species in response to little or no oxygen availability to the roots.
Optimal trap height for monitoring ambrosia beetles should be placed at ¿ 1.7 meters.
Ethanol-baited traps, ethanol-injected trees, and traps baited with bolts from ethanol-injected trees are useful indicators of seasonal activity for predicting attacks and timing insecticide applications. However, the magnitude of beetle activity varied depending on the method; presumably due to ethanol emission rates.
Any “ethanol-related” treatment method can be used in grower-based monitoring programs because all were effective predictors of tree attacks. Although some treatments like ethanol trunk injections resulted in a greater total beetle response, presence of beetles in traps was equally predictive of the timing of tree attacks and the traps were easier to deploy.
In Tennessee, first activity of ambrosia beetles tends to occur from mid-March to early April. To detect first flight, traps should be deployed by early to mid-March in Tennessee.
Ethanol injected bolts can be stored for several months and still retain their attractiveness for inducing ambrosia beetle attacks as part of monitoring programs.
Trees injected with ethanol sustained higher ambrosia beetle attacks than trees not injected with ethanol. Ethanol trunk injections also induced more attacks than baiting trees with an ethanol lure.
A variety of deciduous tree species injected with ethanol were readily attacked by ambrosia beetles. Variability in cumulative attacks among species occurred between years, which indicate factors other than tree species influence ambrosia beetle colonization behavior. Variability in ethanol emission is believed to account for variability in attacks.
No ambrosia beetle attacks occurred on flood-stressed sugar maples, but high numbers of attacks occurred on adjacent ethanol-injected sugar maples. Thus, ethanol-injected trees might be useful as trap trees to pull beetles away from trees naturally-stressed trees.
The first trap capture of granulate ambrosia beetle in Tennessee occurred almost simultaneously with the first redbud bloom during three consecutive years, which suggests that plant phenology may be a suitable predictor of beetle activity for timing of spray treatments.
Heat accumulation (i.e., degree days) did not reliably predict emergence of X. crassiusculus from 2004-2010 in Tennessee. First trap capture of granulate ambrosia beetle occurred between 118 and 253 growing degree days (base 50 oF) over a 6-year period.
The wide range of growing degree day intervals suggests heat accumulation is not the only factor affecting beetle activity.
The permethrin-based conventional insecticide Perm-Up and botanical insecticide Armorex were the most effective in their respective classes for minimizing ambrosia beetle attacks, but neither product provided 100% control on ethanol-injected trees.
Combination treatments of permethrin with biopesticides did not provide a greater advantage over using the products alone.
Systemic insecticides were not effective at preventing attacks when applied either as trunk sprays or as soil drenches.
Spring is the most active period for ambrosia beetle colonization. Insecticide tests performed from April to June averaged 3.1¿ more ambrosia beetle attacks than tests performed from June to August.
A wetting agent and a polymer did not improve insecticide efficacy or residual activity.
Ambrosia beetles attacked trees during all time periods of the day, but early morning and late evening were peak flight and gallery formation periods.
This research relates to the following objectives of the parent project: (1) to reduce, through knowledge generated by research, crop losses and damage caused by insect pests of ornamental nursery crops, turf, and other horticultural crops; (2) to develop alternative management strategies for pest control that will reduce dependence upon traditional uses of insecticides, and lessen impact on groundwater.