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Published October 22, 2012, 10:26 AM

New Challenges

If it stays dry in 2013, farmers can be less concerned about spraying to protect crops from white mold in dry edible beans, sunflower and canola. But that doesn’t mean disease troubles are over.

By: Mikkel Pates, Agweek

FARGO, N.D. — If it stays dry in 2013, farmers can be less concerned about spraying to protect crops from white mold in dry edible beans, sunflower and canola. But that doesn’t mean disease troubles are over.

Sam Markell, North Dakota State University Extension plant pathologist for broad-leafed crops, says there is a different set of dry-

season crop diseases that could rear its ugly head.

“Some of the rusts, soybean cyst nematodes, will become a major issue in dry environments,” Markell says. The nematodes have shown up in many counties, but haven’t produced much yield loss because the overall plant vigor overcame the effects of the disease.

“Some of the root rots that we haven’t seen a whole lot of will really start to show up,” Markell says. “It’s not necessarily because the environment is more favorable — root rots love water — but when plants are moisture-stressed, any kind of damage to the root is going to cause problems. Whereas if you have minor root rot problems, and it’s wet, and they don’t have to try real hard (to survive) you might not see that as obviously as when it’s dry.”

Markell says farmers also will see more charcoal rot, predominantly in soybeans, and dry edible beans and even corn and sunflowers. “We started to see quite a bit of it in soybeans this fall,” he says. “Charcoal rot likes it hot and dry.”

Rust losses

NDSU is doing a survey of the eastern half of North Dakota, where most of the soybeans are grown. “A lot of the stuff we’re getting in has charcoal rot in the stems,” Markell says. “We’re seeing it all over the place. We wouldn’t have seen that in 2009 because it was cold and wet.”

Markell says anything beyond a seven-day weather forecast has its uncertainties, but there is increasing concern about whether farmers are entering a drier, more normal cropping situation. “It’s important for farmers to realize the diseases you deal with are different in wet versus dry years,” Markell says.

Yield reductions from the dry season diseases probably will increase if it stays dry in 2013. “The plants were stressed in areas (in 2012); that’s clear,” Markell says. “I think the subsoil moisture got us through the year pretty well. I think these diseases are going to get worse if the plants are really moisture-Soybean cyst nematode will take a big chunk out of yield when it’s dry, he says. “The roots are stressed; they have a living parasite on them, and if there’s not available water, they’re really going to have trouble pulling up the moisture.”

Historically, the most significant losses to rusts — dry bean rust, sunflower rusts and certain types of the wheat rusts — are greatest when it’s dry. “Rust can occur anytime, but it doesn’t need rainfall. It needs dew, and we can still have dew in a drought year.”

Rust creates open wounds on the plant. “They’ll just leak moisture away,” Markell says. “So when you have a lot of drought and a lot of rust plants really turn dry and crispy pretty quickly, there’s greater yield loss.”

There have been genetic improvements against rust in most crops since the last rust outbreaks, but the pathogens have changed too, Markell says.

Constant battle

“It’s kind of this battle that goes back and forth between the breeders and pathologists and the pathogen itself,” he says. “The last time we had dry weather, dry bean rust was a big problem. There was a resistance gene that was put in in the mid-1990s and rust in dry beans became a non-issue until 2009. There was a new race that was formed, so they’re now susceptible again.”

Wheat rusts are more variable.

There are three wheat rusts in the region — leaf rust, stripe rust and the always-lurking stem rust. “Those resistance genes have changed quite a bit in the last 20 to 25 years, and so has the pathogen,” Markell says. “It’s always a threat.”

Sunflower rust is similar, except fewer resistance genes have been put into varieties, compared with wheat or dry beans. Sunflowers have other problems that are the prime targets of breeders, he says.

There are good fungicides to deal with crop diseases today. “If you leave rust unchecked and you have a pretty big epidemic, it can reduce a lot of crops to just a fraction of what they would normally yield. But if you get in there early enough and put a good fungicide on it, and maybe a (subsequent) application, you can mitigate a lot of that damage.”

It’s harder to decide to invest in fungicide in dry years because the economics aren’t as good in years of adequate moisture and better yield potential, Markell acknowledges.

Wheat rusts all blow in from the south. Sunflower and dry bean rust pathogens are able to overwinter in North Dakota. “They are resident here,” he says.

As a general rule, rusts have tough spores. They can blow hundreds of miles. Fungicides that work on rust in a wet year also will work on rust in a dry year, Markell says. For a bulletin called “Row Crop Diseases in Drought Years,” written in 2008, the last dry year, go to www.ag.ndsu.edu.stressed.”

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