Rhizoctonia and wilt create challenges for potato growers

Potatoes, like most other crops in the Klamath Basin, are running about two weeks late because of the cool spring. The difference between two weeks late in the Klamath Basin and other parts of California is the shorter growing season.

John Crawford, part owner of Crawford Farms Inc. for commercial farming and Cascade Farms for organic farming in Tulelake, said everyone across the country is two weeks behind on their potatoes.

"I think two weeks behind is going to equate to smaller potatoes, which are going to equate to smaller yields, which are going to offset any additional acres that may have been planted based on last year's really good (organic potato) market," Crawford said. "I really don't think at the end of the day we're going to have many more potatoes to sell than we had a year ago. And that will be a good thing for the market."

Sid Staunton of Tulelake also raises conventional and organic potatoes. Staunton agreed the weather will impact yield. The cool spring also contributed to problems with rhizoctonia disease, he said. Rhizoctonia girdles the roots and the stem, then the plant withers and yield is reduced.

"If we have really warm conditions and we can get that plant to come up quicker, then we'll have less rhizoc. And it can be more variety sensitive as well. I planted some reds and they don't seem like they're as susceptible as the russets," Staunton said.

Rhizoctonia was a huge problem in Crawford's conventional potatoes and crops would have a 100 percent infection rate. Now, with new chemical compounds, he has good control. But Crawford said he continues to struggle with rhizoctonia in his organic potatoes.

"It's our worst enemy in organics because we really don't have a natural compound that is very good at fighting it," he said, adding in one field of organic potatoes he estimates 75 percent are infected with rhizoctonia.

Staunton said he has the same difficulties in controlling the rhizoctonia in his organic potatoes.

"Basically with the organic spectrum, you're really reduced with your toolbox, so your fungicide choices are pretty limited," he said.

"Rhizoctonia in organic potato production is like going back before we had the chemistries we use now for conventional potatoes," Staunton said. "It feels like we're in a time capsule. We're back in the 70s and early 80s when we were kids growing potatoes with our father, and just the tools that we had at that time."

There are some tools to fight the rhizoctonia in organic potatoes.

"We're putting a couple of treatments on the seed," Crawford said, but it's not enough to control the disease.

Crawford estimated at least a 20 percent yield loss from rhizoctonia damage.

Staunton has seen a similar reduction in yield, 20 percent to 25 percent.

"There are some fungicides, copper-based fungicides," he said, but some of the organics are grown on wildlife refuge lease land where copper products are prohibited. "What we're doing currently is, we're using a lot of compost tea, and we use a fungicide product in the furrow."

Rob Wilson, center director/farm advisor of the University of California Intermountain Research and Extension Center in Tulelake, has been doing research on rhizoctonia and verticillium wilt disease, both problems for organic and conventional potato growers.

Growers have been seeing more problems with both of these diseases, Wilson said.

Wilson has looked at fumigation for verticillium wilt in potatoes. This year, he will also look at fumigation in combination with biological control products and using biological control products alone.

"We've also been looking at irrigation and the frequency of irrigation on both of these different pathogens that are in potatoes," Wilson said.

"There's been some work to suggest that saturated soil conditions early in the season can sometimes promote verticillium wilt, and then sometimes drought-stress conditions later in the season can promote verticillium wilt," Wilson said, adding that he is trying to determine if that has an influence on disease.

"Last year we did that and we didn't see any significant differences, but the disease pressure was relatively low in the field," Wilson said, adding this year there is heavy disease pressure, so he will do a comparison between the two years.

Rhizoctonia is present in a lot of the soils, too, Wilson said: "It's a common problem on potatoes for a lot of producers, but it's especially difficult for the organic producers."

Rhizoctonia causes black scurf on potatoes. It's a blemish on the skin of the potatoes that is a problem for conventional producers and a big problem for the organic producers, Wilson said.

"We did some work with traditional fungicides last year and we saw some reduction to rhizoctonia from fungicide applications," Wilson said.

Wilson is currently looking at biological control for rhizoctonia that includes beneficial bacteria and fungi that will provide suppression of the disease without the use of fungicides.

That would be beneficial to conventional growers to use in combination with fungicides, and for organic producers who need a non-fungicide method to control rhizoctonia in potatoes, Wilson said.

"We don't have the results this year from the biological," Wilson said.

Screening the seed potatoes for rhizoctonia is an option for growers, Wilson said. There is a researcher at Oregon State University who is looking at the influence of seed source on rhizoctonia pressure, he added.

"You can buy seed that's clean of rhizoctonia, but there's a cost premium for that, and it's unknown if planting a clean seed in contaminated soil will be a benefit," he said.

(Kathy Coatney is a reporter in Corning. She may be contacted at kacoatney@gmail.com.)