Michigan 1995 Late Blight Education and Management Plan

Michigan 1995 Late Blight Education and Management Plan

Summary

This grant has made a positive contribution to controlling potato late blight in Michigan as well as contributing to the world wide pool of information on potato blight control. The goal of this program was to reduce fungicide use and control disease. Using the data from the Michigan Potato Industry’s 1995 pest survey, the majority of Michigan growers indicated they used 9-15 applications of fungicide to control potato late blight (1995 Pest Survey p-21). Control costs were approximately $92 per acre.

The spread of potato late blight disease is directly related to the presence of inoculum and weather conditions. This project specifically addressed reduced pesticide use. It was necessary to recommend to growers that they adhere closely to fungicide recommendations during the 1996 growing season in order to stop the spread of disease (W.W. Kirk, Late Blight Control Guide), which was known to exist in many Michigan locations.

U.S. potato growers are facing a steep learning curve with regard to understanding the life cycle of the disease and control measures. Debate ranges from the importance of disease-free seed to treating fields infected with disease, and preventing the disease from infecting the crop. This project funded the salary, fringe benefits, travel, and supplies for a visiting assistant professor position within the Botany and Plant Pathology Department of Michigan State University. William W. Kirk was hired with a 50 percent extension and 50 percent research appointment with funds provided by the Michigan Potato Industry. This grant provided some of the funding necessary to pay salary, fringe benefits, and travel. All of the objectives of the grant were attempted, however, results may not be evident for several years.

Due to the nature of the disease and currently registered fungicides, it is necessary to be on a protective spray program. Reducing pesticide use may not be immediately possible, however, with increased management education and a minimum-use program is in place. The cost of control ($92 per acre, 1995 Pest Survey) and expected cost of control $150 per acre for the 1996 crop will encourage a minimum-use program.

Identifying disease is a one on one educational process. When Kirk showed two growers diseased tissue from potatoes grown at the MSU Muck Research Farm. In this particular situation the growers indicated they had never seen late potato blight. Scouting fields requires highly trained people. Training occurred at meetings, seminars, and field days. The meetings are held at several locations across the state.

Growers were encouraged to contact Kirk to determine when to destroy a part of the crop. During the 1996 season, several small portions of late blight infected fields were eradicated.

Monitoring resistant to metalaxyl is becoming less important since all new late blight finds are A-2 strain or metalaxyl resistant. Continued testing will go on at the MSU late blight lab, however, all recommendations are based on A-2 US strain 8, being the population growers must control.

Since resistant populations are most prevalent and control products are geared to resistant populations, all emphasis and recommendations are for resistant populations.

Emphasis at meetings, seminars, and field days during the period of this grant has been placed on management, including properly disposing of cull piles, killing of volunteer potatoes, planting non infected seed, early protective sprays, use of sec. 18 fungicides, complete spray coverage of crop, eradication of areas showing greater than 20 percent infection, vine desiccation, and clean harvest.

The spread of potato late blight is a community problem, which includes home gardeners, weed plants and tomato plants. The spread of the disease was discussed at meetings, seminars, and field days throughout the year. A Late Blight Control Guide (W.W. Kirk April 1996) published for the purpose of educating growers outlines the spread of the disease.

Growers have been made aware of the transmission of disease by infected seed. In February 1996 a special seminar was held at the 1996 Michigan Winter Potato Conference to discuss seed and its role in infecting a crop. Kirk has been invited to be the guest speaker at the December 1996 National Potato Council Seed Seminar to discuss late blight and seed issues. A follow-up seminar will be held at the 1997 Michigan Winter Potato Conference.

The Michigan Potato Industry will continue with the extension and research activities established by this grant for at least the next two years. The MPIC will continue its annual Pest Survey, including requesting information from growers on late blight and reporting information to EPA. Small plot fungicide trials and field trials will continue. Potato late blight will be a topic for discussion at various events.