In the Field Spud Smart Spring 2011

Storecast: Predicting the Future Health of Potatoes in Storage

FOR THE FIRST time, a tool is now available to growers for determining the risk of disease to potatoes in storage. The recent commercialization of this novel diagnostic tool may assist producers with their in-storage disease management programs. Pest Pros Inc., an independent crop consulting firm and plant disease diagnostic laboratory, located in Plainfield, Wis., has developed and commercialized the first system of its kind to test for the probability of developing potato storage diseases during the growing season before the potatoes are harvested. Using the polymerase chain reaction, a scientific technique used to amplify DNA, the relative risk of disease potential in storage for pink rot, pythium and soft rot can be determined. Dry rot, silver scurf, early blight and black dot can also be included in the pathogen screen.

Storecast_1Pest Pros’ Storage Potato Disease Risk Indexing System is called Storecast, and is to be used by growers as a storage disease and inventory management tool. Testing involves collecting healthy-looking tubers from the field before harvest, cleaning and juicing them, and then extracting their genetic material. The ultimate goal is to provide a means for growers to segregate their “risky” potatoes from their healthy potatoes—by variety in storage—and manage the quality of healthy potatoes in long-term storage.

A good harvest doesn’t automatically mean a good year for potato growers. “Every year, about eight to nine per cent of the potato crop in the United States goes bad in storage facilities before being shipped to chip and french fry processors. That translates into a loss of about $16 million in Wisconsin alone,” says Randy Van Haren, lead pest management specialist for Pest Pros.

In an effort to curb this type of loss, the Storecast system was developed to enable farmers to better separate potatoes that are fit for long-term storage from those that are not.

Using the scientific technique called real-time polymerase chain reaction, qualified lab technicians examine the DNA contained in each sample to determine the percentage of foreign microbial agents, such as those responsible for the onset of late blight, pink rot and soft rot in stored potatoes, which can potentially cause storage losses.

The results of the in-field tests are used to inform farmers on a field-by-field basis which potatoes have high levels of microbes and, thus, a high probability for the development of disease at some stage in storage. A grower can then base storage management decisions on this prediction concerning specific fields and potato lots at harvest and storage time. Specific problematic lots can be stored separately or shipped off to processors soon after harvest.

In general, the testing process involves sampling fields one to three weeks prior to harvest by digging a three-tuber sample for each 10 acres from the interior of the fields. Only asymptomatic tubers are sampled and tested. DNA is extracted from the tubers using real-time PCR to test for the presence of pathogens. Each field is indexed for rot potential in storage. The results are then generated in the lab and reported approximately one week later to the grower, and storage inventory management is discussed at that time. Tubers are then monitored in storage for disease outcome.

“Each field site and storage bin, in effect, becomes a data point, which provides detailed insight into the potential for storage rots based on test results. Refinements in storage management can be made over time to adjust to the results obtained through the Storecast system,” says Van Haren. Therefore, potato lots with a higher probability of developing disease can be moved prior to those with a lower predicted risk of being infected with disease-causing pathogens.

Fields are indexed for storage rot potential from 1 – 5 (low to high) based on the composite PCR test results for the individual samples.


Since 2004, Pest Pros has collaborated with scientists at the University of Wisconsin-Madison on this project to fast-track the system’s commercial application. Walt Stevenson and Zahi Atallhah, plant pathologists and potato specialists at UW-Madison, were instrumental in helping to eventually commercialize the test, says Van Haren.

Trials on 142 fields comparing index predictions to final storage outcomes were performed during three growing seasons, from 2008 to 2010. During this time, 108 commercial potato fields for processing were tested pre-harvest to determine potential storage disease risk. The fields were indexed from 1 – 5 (low to high) for disease risk, and the storage bins were monitored and rated from 1 – 5 (low to high) for the development of storage rot.

A comparison of the Storage Potato Disease Risk Index to the storage rot outcome shows that 82 per cent of the forecasted disease predications were either in complete agreement or very close to the final disease outcome in storage for processing Russet Burbank, and 73 per cent for chipping varieties. These results were produced in average to slightly below average years for storage rot in Wisconsin.

Twenty-five per cent of the forecasts tended to overestimate the potential for rot on chipping varieties, compared to 11 per cent on Russet Burbank. Over the testing period of three seasons, there was only a two per cent rate of the occurrence of substantially more rot than expected. These results have paved the way for full commercialization of the system.

This testing program can be tailored to fit geographic or varietal differences, says Van Haren. Also, the program has the flexibility to increase or decrease the number of samples per field as required, he says.

Testing using the Storecast system is available to Canadians if growers, or consultants, pull their own tuber samples, sending frozen, juiced samples to Pest Pros in the United States.

This assay is the first of many PCR-based diagnostic tests that Pest Pros plans to offer growers. “PCR is very fast and very sensitive,” Van Haren says. “The future of growth in our business is going to be in PCR technology.”

Lukie Pieterse