Ecology and Management of Exotic Ambrosia Beetles
Producers of nursery grown trees incur considerable risk because trees must be maintained for several years before they become salable. During this time trees are susceptible to damage from many sources including insect pests. In the past decade, North Carolina nurseries have faced increased risk of insect damage to many varieties of trees due to introduction of granulate ambrosia beetle (GAB), Xylosandrus crassiusculus, from Asia. Female GAB emerge in spring, bore into the trunks of young trees, and excavate galleries in the heartwood. In addition, female beetles inoculate trees with ambrosia fungus which blocks xylem vessels. Infested plants die from boring damage, ambrosia fungus, or infection by a secondary pathogen.
GAB are protected from insecticides once inside a tree. Therefore, the current management recommendation is to spray the bark of susceptible trees with permethrin insecticide when beetles emerge in spring and to repeat these applications until beetle activity subsides about 12 weeks later. Despite this intense insecticide regimen, growers continue to have trees damaged by GAB. This indicates the current management strategy needs refined to optimize efficacy.
Currently we have three projects designed to optimize GAB management by reducing plant damage and non-target effects of insecticide applications. See project descriptions below.
Statewide granulate ambrosia beetle monitoring and alert program
The overall objective of this project is to prevent economic loss by informing nursery and landscape professionals when preventative insecticide applications are necessary to protect trees from Granulate Ambrosia Beetle damage. To achieve this, a pilot monitoring and alert program will be established with three specific objectives:
- To monitor and collect data on Granulate Ambrosia Beetle across North Carolina;
- To set up an email system that will inform nursery and landscape professionals when Granulate Ambrosia Beetle is active in their region;
Evaluation of application methods to reduce insecticide use and improve IPM of Granulate Ambrosia Beetle
GAB are protected from contact insecticides once inside a tree and systemic insecticides are ineffective because they do not ingest vascular tissue. Therefore, the current management recommendation is to spray the bark of susceptible trees with a pyrethroid insecticide when beetles emerge in spring and to repeat these applications every 2-3 weeks until beetle activity subsides about 12 weeks later. Pyrethroid applications are typically made with airblast sprayers that produce a fine insecticide mist. This application method allows growers to treat a large number of trees in a short amount of time. However, only a small portion of the insecticide contacts the trees while the rest settles on the ground or elsewhere in the environment. Thus far more active ingredient is released into the environment than is required to effectively manage the pest. Increasing environmental regulations, consumer concern about pesticide use, and a slowing economy mean that growers need to apply insecticides in a more judicious and economical way.
Targeted insecticide applications are a cornerstone of IPM. Routine, broadcast applications of broad spectrum insecticides have been shown to increase scale and mite populations in ornamental trees by killing natural enemies. An alternative application methods is to apply insecticide directly to tree trunks thus reducing waste and environmental harm. This method, developed by a local grower, uses a backpack sprayer and a spray wand with 2 opposing nozzles eight inches apart. Both sides of a tree can be sprayed with a single pass down the trunk. Growers who use these methods estimate they use 90% less active ingredient compared to an airblast sprayer. The same growers also believe they get better coverage and efficacy using manual application. The trade off is that more time is required compared to airblast applications.
Applying insecticides directly to tree trunks rather than broadcasting it throughout a nursery will reduce the quantity of active ingredient released into the environment and the impact of this insecticide regimen on non-target organisms. However, adoption of more labor intensive application methods relies on demonstrating the economics and efficacy of the procedures. Therefore, the objective of this research is to compare efficacy, environmental impact, and cost associated with manual application methods to conventional airblast sprayer applications.
Objectives: In this project we will evaluate using an airblast sprayer and dual-nozzle backpack sprayer for the application of permethrin to:
- Evaluate the efficacy of each method by measuring insecticide coverage and incidence of GAB damage
- Evaluate the environmental impact of each method by measuring active ingredient released, insecticide residue on unintended surfaces, and effect on beneficial arthropods
- Evaluate the economic cost of each method by measuring product, labor, and plant damage expenses
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Duration of permethrin efficacy against Granulate Ambrosia Beetle
Current management recommendation is to spray the bark of susceptible trees with permethrin insecticide when beetles emerge in spring and to repeat these applications every 1-3 weeks until beetle activity subsides about 12 weeks later. Despite this intense insecticide regimen, growers continue to have trees damaged by GAB. This indicates the current management strategy needs refined to optimize efficacy. One way current management could be optimized is to determine exactly how long permenthrin applications are effective and under what conditions.
There are many inconsistencies in how growers apply permethrin to susceptible trees. Growers vary in frequency of application from 1 to 3 weeks. It is likely that residual efficacy ceases before another application is made. In addition, some growers use spreader-sticker products to try and increase the amount of product that adheres to tree bark and the duration of efficacy. Thus, under some treatment regimens growers are leaving trees unprotected for a period of time between applications if permethrin becomes inactive or does not adhere to bark. In other cases growers may make more applications than are necessary to effectively protect trees. Unfortunately no research is available to help growers determine how to achieve maximum efficacy with minimum input. Therefore, it is essential to document the duration of permethrin efficacy applied at different intervals with and without a spreader-sticker additive.
The overall objective of this project is to prevent economic loss by optimizing efficacy of insecticide applications to protect trees from Granulate Ambrosia Beetle (GAB) attack.
To achieve this, an experiment will be conducted in two North Carolina nurseries to determine:
- The frequency of permethrin application that maximizes efficacy;
- If spreader-sticker additives increase the level or duration of permethrin efficacy.