Potato Grower

12 Potato Grower | IDAHO ANNUAL 2015 LOADS TO ALL POINTS IN USA-CANADA-MEXICO Magic Valley Truck Brokers, Inc. Keep on Truckin' "Your Friendly Truck Brokers" Boise, ID 800-635-3053 (Fax) 208-377-0956 team@magicvalleytruckbrokers.com www.magicvalleytruckbrokers.com "Those who snooze lose." Bonded & Licensed Truck Broker 147016MagVal112.indd 1 5/27/14 8:20 AM Rotten Luck An overview of late blight in Idaho in 2015 UNIVERSITY OF IDAHO By Phillip Wharton Over the past couple of years, potato growers in Idaho have had increasing problems with potato late blight caused by Phytophthora infestans. Prior to 2014, late blight epidemics in Idaho were sporadic, tending to show up late in the growing season, and were restricted to just a couple of fields. In 2013, we had the first report in Idaho of a new strain of the late blight pathogen, US-23, in an outbreak limited to a couple of fields in Bingham and Madison Counties. This was followed in 2014 by a larger epidemic in southeastern Idaho, which was favored by the unusually mild and wet weather in late July and August. Traditionally, late blight epidemics in Idaho are thought to start from infected seed that has been imported into the state, as winters are usually too cold for the pathogen to survive in infected tubers. Recent studies have shown that mycelia of newer genotypes of P. infestans such as US-23 are becoming more tolerant to cold temperatures and are tolerant to 27 degrees for up to three days' continuous exposure. This, combined with the recent trend of warmer winters, means more infected volunteer and cull pile potatoes are surviving the winter and acting as sources of disease inoculum in the spring. In 2015, the mild winter weather resulted in a large number of volunteer potatoes surviving the winter. Combined with almost daily rain showers in May, this made for ideal conditions for the initiation of late blight epidemics. This year late blight was first reported on potatoes in Bingham County on July 10, one of the earliest dates late blight has been reported in the last 15 years. With frequent, almost daily rain showers and thunderstorms moving through the Snake River Plain in southeastern Idaho in July and early August, conditions were ideal for the spread of late blight. By mid-August, late blight had been reported as almost endemic in Bingham, Bonneville, Cassia, Fremont, Jefferson, Madison, Minidoka and Power Counties. Fortunately, growers who adopted a late blight program early in the season and applied products in a timely manner were able to minimize losses from the disease. However, this came at an increased cost. Base-maintenance fungicides for potato foliar disease control in Idaho would normally be about $60 to $80 per acre per season, but in 2015 this cost rose by to $150 to $180 per acre per season due to increased frequency of applications and more use of containment fungicides. In addition, growers had to protect tubers going into long-term storage with disinfectant products. Reports of tuber late blight coming out of the field have been higher than in previous years. There was even a confirmed report of tuber late blight from Payette County, which was unusual, as there were no reported outbreaks of foliar late blight in southwestern Idaho this year. Although there is a likelihood of more late blight-infected tubers going into storage this year, growers can minimize the risk of the disease spreading in storage by making an application of phosphorous acid on tubers going into storage. Research from UI has shown that applying phosphorous acid on infected and healthy tubers going into storage can limit disease severity in storage to 1 percent or less. Although it is impossible to cure infected tubers, the phosphorous acid will prevent the spread of the disease to healthy tubers. With the trend toward warmer winters and wetter springs and summers, the prognosis for 2016 could be more late blight. With the large number of infected fields in southeastern Idaho in 2015, the likelihood of late blight surviving the winter in volunteer or cull potatoes is high if we have similar conditions to last year. With the El Niño building in the Pacific Ocean, the National Oceanic and Atmospheric Administration is predicting a warmer and wetter than average winter for the Pacific Northwest; as such, growers should probably plan for another high-risk late blight year in 2016. PG APPLYING PHOSPHOROUS ACID ON TUBERS GOING INTO STORAGE CAN LIMIT DISEASE SEVERITY IN STORAGE TO 1 PERCENT OR LESS. GROWERS WHO ADOPTED A LATE BLIGHT PROGRAM EARLY IN THE SEASON WERE ABLE TO MINIMIZE LOSSES FROM THE DISEASE. HOWEVER, THIS CAME AT AN INCREASED COST.

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