A Multi-Faceted Approach to Managing Powdery Mildew on Organic Table Grapes in Southwest Idaho

A Multi-Faceted Approach to Managing Powdery Mildew on Organic Table Grapes in Southwest Idaho

Summary

Organic table grape production is a good match for southwest Idaho’s rapidly changing agricultural landscape. Producer Mike Medes of Rocky Fence Vineyard grows organic table grapes on nine acres outside Emmett, Idaho, and planned to market his grapes directly to local, regional and international customers in 2007, but powdery mildew destroyed 92% of his fresh market crop. Medes contacted University of Idaho Extension to help him research and manage this disease. We applied to WSARE for funding to assist him and the dozens of growers entering this new industry.

The results of our collaborative project are exceeding our expectations. Our teams’ applied research and subsequent recommended practices have contributed significantly to the viability of producer Mike Medes, and have caught the attention of both conventional and organic table grape growers across the region. Medes is averaging 6,000 pounds of marketable fruit per acre, and the growing Idaho table grape industry is eagerly anticipating our published results that will positively contribute to their success.

Objectives/Performance Targets

In early 2009, we continued the work begun in February 2008, selecting vine samples for evaluation of overwintering fungus and choosing and marking vines to serve as sources for inoculum testing throughout the season. In mid-April, we recommended a preventative spray of OMRI approved superior-type oil or Lime-sulfur be applied to the dormant, pruned canes. Medes also worked to convert the last of the vineyard from “T” trellises to the recommended “Y” style.

Bud break occurred in early May, at which point Medes began applying preventative treatments of Sulfur DF every 14 days at the rate of 6 lbs/acre. At this time, no fungus was detected within the buds. We have learned now that in Idaho, winter temperatures do not allow the fungus to overwinter inside the buds, which is common in California vineyards.

Throughout the spring and summer, Ariel Agenbroad and Tony McCammon and kept in close contact with Medes and sent samples to Krishna Mohan to test for presence of powdery mildew fungus. We had planned to collect local Idaho weather data to use with University of California Grape Powdery Mildew Risk Assessment Index (http://www.ipm.ucdavis.edu/calludt.cgi/GRAPEPMVIEW1 ), a modeling tool that correlates daily heat information with the onset of disease, calculates disease spread and then advises timing of treatments. However, as in 2008, well timed preventative treatments and cooperative weather conditions meant that the vineyard was clean in 2009 and we were unable to detect the powdery mildew fungus visually or microscopically at any point. While this was a very good thing for Medes, it did not give us a chance to implement the disease modeling tool or try any alternative treatment sprays except for compost tea.

In October, 2009 and early January, 2010, we sent samples of compost and compost tea to Soil Foodweb® in Corvallis, OR, to explore the powdery mildew-inhibiting effects, if any, present in these materials. We are currently processing the results of this test and interpreting the results.

• Introductory Project Poster

Accomplishments/Milestones

In August, for the second year in a row, Medes successfully grew, harvested and marketed more than 6000 pounds/acre of disease free, high quality Idaho table grapes to local, regional and international customers.

Impacts and Contributions/Outcomes

We have been extremely lucky to be working with such a dedicated and capable producer partner. Medes feels that it is important to be open and share his successes and failures with other new growers in the industry. In September 2008 and August 2009, we held field days/tours at Rocky Fence Vineyard, attended by over 35 participants each time. Medes led groups on a comprehensive overview of the practices and techniques implemented during the project and answered dozens of questions.

Throughout the project we have been documenting our treatments, progress and results with photographs, interviews and video clips for reports, outreach materials and publications. The protocols we are developing through this research will be available soon as University of Idaho Extension recommendations for powdery mildew management specific to organic table grape production in our region. Information will be distributed to producers and professionals when it is available.

Our introductory poster and handouts were displayed at our field days. Our poster was also selected for display at the Sub-regional meeting of Western SARE in Spokane, WA in February 2009, and presented at the 2nd Annual SW Idaho Organic Producers School in Boise and an Organic Certification Workshop in Emmett in August 2009. Ariel Agenbroad has also been invited to attend the New Mexico Organic Conference in February 2010 and present a poster on this project.

Articles about this project have been published by Ag Weekly (http://www.agweekly.com/, September 2008), Bringing Home the Harvest (Rural Roots, Inc. Vol. 10, Issue 1, 2008), and University of Idaho College of Agriculture and Life Sciences News (http://www.extension.uidaho.edu/news.asp, August 2008 and 2009).

Articles in development have also been solicited by editors of Sustaining the Pacific Northwest (Washington State University) and The Farmer Exchange (Northwest Coalition for Alternatives to Pesticides).

A setback to our timeline occurred in June 2009, when the University of Idaho proposed closing the Parma Research and Extension Center, where two of our project partners, Dr. Esmaeil Fallahi and Dr. Krishna Mohan, are stationed. The surprise announcement was a shock to the faculty and staff at the Parma Center, local producers, and the community. A major effort was undertaken to postpone the action and raise funds.

One unplanned result was that Tony McCammon, Mike Medes and I had limited access to our specialists this summer and fall to aid us in processing our research data and creating publishable protocols and other outreach materials. However, in early December, it was announced that the Idaho State Board of Education had approved from the Simplot Company to fund the Parma Center for the next five years. With our specialists secure and once again available, we are back on track to finish creating our outreach materials, publish our findings, and look to a brighter future of additional research in table grapes.

• 2009 Field Day
• 2010 Project Poster
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Collaborators: