Developing a media moisture threshold for nurseries to reduce tree stress and ambrosia beetle attacks

Authors: FRANK, STEVEN - North Carolina State University; Ranger, Christopher

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2016
Publication Date: 7/12/2016
Publication URL: http://handle.nal.usda.gov/10113/63344
Citation: Frank, S.D., Ranger, C.M. 2016. Developing a media moisture threshold for nurseries to reduce tree stress and ambrosia beetle attacks. Environmental Entomology. doi: 10.1093/ee/nvw076.

Interpretive Summary: Exotic ambrosia beetles are among the most damaging pests of trees grown in nurseries. The primary pests Xylosandrus crassiusculus Motschulsky and Xylosandrus germanus Blandford use ethanol to locate vulnerable trees. Research and field observations have shown that flood-stressed trees emit ethanol and are preferentially attacked by ambrosia beetles. Our goal was to develop a media moisture threshold as an integrated pest management tactic and assess grower practices that lead to ambrosia beetle attacks. Flooded trees sustained more attacks than unflooded trees which were not attacked. To determine optimal media moisture levels we grew flood-tolerant Acer rubrum L. and flood-intolerant C. florida in containers with 10, 30, 50, 70, or 90% media moisture. No flooded or unflooded A. rubrum were attacked. However, C. florida grown in 70% or 90% moisture were attacked and died whereas trees at 30% and 50% moisture were not attacked. Thus, we suggest a moisture threshold of 50% when growing C. florida and other flood intolerant trees. However, during peak ambrosia beetle flight activity in spring 2013 and 2014, we found that media moisture levels in commercial nurseries were often between 50% and 90%. Implementing a media moisture threshold, as a new IPM tool, could reduce ambrosia beetle attacks and the need for insecticide applications, which is currently the only available management tactic. Future research should focus on how changes in substrates, irrigation, and other practices could help growers meet this threshold.

Technical Abstract: Exotic ambrosia beetles are among the most damaging pests of trees grown in nurseries. The primary pests Xylosandrus crassiusculus Motschulsky and Xylosandrus germanus Blandford use ethanol to locate vulnerable trees. Research, primarily with X. germanus, has shown that flood-stressed trees emit ethanol and are preferentially attacked by ambrosia beetles. Our goal was to develop a media moisture threshold as an IPM tactic and assess grower practices that lead to ambrosia beetle attacks. Flooded Cornus florida L., Cornus kousa Burg., and Magnolia grandiflora L. trees incurred more attacks than unflooded trees which were not attacked. To determine optimal media moisture levels we grew flood-tolerant Acer rubrum L. and flood-intolerant C. florida in containers with 10, 30, 50, 70, or 90% media moisture. No flooded or unflooded A. rubrum were attacked. However, C. florida grown in 70% or 90% moisture were attacked and died whereas trees at 30% and 50% moisture were not attacked. Thus, we suggest a moisture threshold of 50% when growing C. florida and other flood intolerant trees. However, during peak ambrosia beetle flight activity in spring 2013 and 2014, we found that media moisture levels in commercial nurseries were often between 50% and 90%. Implementing a media moisture threshold, as a new IPM tool, could reduce ambrosia beetle attacks and the need for insecticide applications, which is currently the only available management tactic. Future research should focus on how changes in substrates, irrigation, and other practices could help growers meet this threshold.