Redefining Strawberry IPM under the Threat of Anthracnose and Strawberry Sap Beetle

Introduction - Strawberry anthracnose and the strawberry sap beetle are emerging and increasingly serious pests of strawberries in New York and other regions in the Northeast. Based on our limited understanding of the bionomics of these pests, the current recommendation for their control is through multiple, calendar-based applications of fungicide and insecticide, which will be expensive and threatens to disrupt current IPM practices. Dr. Greg English-Loeb and I received funding through various sources to begin to look at the joint biology of anthracnose and strawberry sap beetle and to develop better management practices for both pests.

The objectives, along with the underlying rationale and early accomplishments of this research are as follows:

1) Survey strawberry fields to determine environmental, horticultural, and management factors influencing the distribution of strawberry anthracnose and the strawberry sap beetle in New York. Although there is some understanding of the factors that contribute to severe problems with anthracnose, there is much we do not understand about the influence of various horticultural practices, such as use of raised beds or drip irrigation, and environmental factors, such as presence of insects or soil type. An extensive survey, measuring these various factors at many farms, will provide a rich data set to identify possible causal relationships that then can be more rigorously examined experimentally.

Accomplishments: A sampling survey of strawberry acreage in New York was conducted in 2002 to determine the distribution of anthracnose and the strawberry sap beetle (SSB) in New York. The 2002 sampling for both pests was conducted in a total of 37 strawberry fields at 14 farms, with farms distributed throughout four agricultural regions of New York. The average number of SSB captured per whole wheat bread dough trap in fields ranged from 0.4 to 53.6. Trap catches of SSB were lower at farms sampled after berries began ripening, suggesting that the beetles are more attracted to ripe strawberries than the bread dough traps. No specific cultural practices or crops surrounding the strawberry fields were clearly linked to the number of SSB captured in the field. SSB was perceived to be a pest in some locations and not in others, despite its presence at all farms. Further work to understand when beetles are moving into fields in New York, what other crops are important food sources for the beetle, and how far the beetles can disperse will be needed to develop strategies for controlling SSB. Although, severe anthracnose epidemics were observed in some fields in western NY in 2002, the disease was found in only one of the 37 fields included in the survey this season. The reason for its conspicuous absence, in what appeared to be a season conducive for a widespread epidemic, is under investigation. Most likely, weather conditions in other regions of the state just prior to or during harvest were not as conducive for disease development as it was in western NY or, because many fields were sampled 1 to 2 weeks prior to harvest, fields were surveyed before significant disease development occurred. It has been hypothesized that SSB may help spread anthracnose throughout strawberry fields, although it was impossible to determine during this survey because the disease was only found in one field. See Vol. 2 No 2 of the NY Berry News for complete details.

2) Evaluate the potential for insects, particularly SSB, to serve as a vector of anthracnose. The survey described under objective 1 can be used to explicitly examine whether problems with anthracnose are associated with the presence of strawberry sap beetle. The 2002 survey did not reveal an association between anthracnose and SSB however, there were issues related to the timing of sampling. Since then, we have conducted some preliminary trials under controlled conditions and determined that the SSB can vector the pathogen in vitro. We are planning to establish a planting in Ithaca to look at their interaction in a designed experiment. The details are not fully worked out. Essentially, we will establish plots and introduce both pests either singly or jointly and monitor the distribution of both pests over time.

Accomplishments: Preliminary studies are currently being conducted by Rebecca Loughner, a graduate student in Dr. Greg English-Loeb's lab; an entomologist a collaborator in this project.

3) Improve the current Integrated Pest Management Program for strawberry by developing a strawberry anthracnose forecaster for use in New York. The statistical relationship between severity of anthracnose and the duration of berry wetness and temperature (principal driving variables) has been developed by Lee Wilson et al. at The Ohio State University. We propose to develop a forecaster for managing strawberry anthracnose based on the infection curves developed by Wilson et al. and the inherent activity of the strobilurin fungicides; the primary class of fungicides used to control anthracnose. A controlled-environment study is currently be conducted to look specifically at how effective the strobilurin fungicides are in controlling anthracnose when applied prior to, but more importantly after an infection event that will generate a known level of disease. For example, at 15 C we can generate 50% disease on mature berries by wetting them for approximately 24 hours, according to the predictive curves developed by Wilson et al. If a strobilurin fungicide is applied 3, 8, or 24 hours prior to the infection event, or 3, 8, or 24 hours after the infection event then we would expect to see distinctly different levels of disease, i.e., control. The experiment we are conducting will examine the pre- and post-infection activity of the strobilurins over a range of climatic conditions.

Accomplishments: We ran preliminary studies to get an understanding of what to expect if a strobilurin fungicide (Quadris 2.08F) was applied at different spray timings. The level of berry infection was measured for berries sprayed with Quadris 2.08F just prior to or 3, 8, and 24 hr after inoculation after exposure to various wetting periods at different temperatures. These timings were chosen based on a combination of factors including how quickly we believe a grower can react after an event has passed and the fact that the strobilurin fungicides have limited after-infection activity against anthracnose. Preliminary results showed that Quadris 2.08F applied post infection can give an appreciable level of control as much as 8 hours after inoculation. We are optimistic that these results are broadly applicable and we plan to look at the pre- and post-infection activity of Quadris 2.08F over a greater range of climatic conditions in an effort to develop a biologically meaningful and cost effective program for managing anthracnose.

Once we have gained a thorough understanding of how the strobilurin fungicides under different scenarios, we can develop strategies for timing applications in effort to keep disease from reaching economically damaging levels and test these in the field. To accomplish this, experimental plots of the day-neutral variety 'Seascape' will be planted and anthracnose fruit rot will be managed according to strictly protective, calendar-based schedules or to rule-based (forecasting) schedules. The final outcome of the study will give growers a tool to time applications of fungicides that will minimize the cost of disease management, improve disease control, and reduce the risk of developing fungicide resistance.