The growers I visited raised several great questions about grape root borer (GRB) that bear reviewing:
1. Why are we seeing this many moths now?
RagApple Lassie began trapping for moths this year in response to damage seen last year. Several vines were declining, and when they were dug up, GRB damage and larvae were present. This was the first GRB damage they recall seeing. It is hard to say why exactly multiple vineyards are seeing significant numbers of GRB, but I suspect that it at least partially due to weather and vineyard age. Last year was the first summer in 3 years with relatively normal precipitation, and soil dwelling insects are often sensitive to moisture--declining in years with low moisture and rebounding following years with moisture.
We also have several "middle age" vineyards in the Yadkin Valley. GRB take up to 2 years complete a generation, so it may take several (8-10 years) for moths to develop to detectable levels. We have several vineyards at or just older than this age.
2. How do we use control tools for GRB?
Lorsban (chlorpyrifos) is the only material registered for GRB, but as I mentioned in my previous post, this material is hard to time given the long GRB emergence time which coincides with harvest.
Soil mounding at the base of vines at the beginning of July is a cultural control option, but I have seem limited efficacy data on this tool.
3. Are there any non chemical options for GRB?
Soil mounding is a non chemical option. Other non chemical options that have been tested include entomopathenogenic nematodoes and pheromone mediated mating disruption. University of Florida researchers have demonstrated good results with mating disruption, but neither of these tools are commercially available at this time. These are both interesting options that bear examination under NC conditions.