Researchers target root rot in sugar beet fields

John O'Connell/Capital Press Carl Staumbaugh, with USDA Agricultural Research Service in Kimberly, Idaho, explains a chart showing rhizoctonia levels in sugar beet piles in Treasure Valley and Magic Valley following his presentation at the Dec. 15 University of Idaho Snake River Sugar Beet Conference in Burley.

Expert warns growers to take proactive measures

By JOHN O'CONNELL

Capital Press

BURLEY, Idaho -- Root rot was abundant in Treasure Valley sugar beet fields this year, according to pile inspection results presented at the recent University of Idaho Snake River Sugar Beet Conference.

Researchers inspected 91 percent of piles from Treasure Valley's 2011 crop and found 60 percent of them showed high levels of root rot, said Carl Strausbaugh, research plant pathologist with the USDA Agricultural Research Service in Kimberly.

All of Treasure Valley's piles had some level of root rot.

In the Magic Valley, 83 percent of beet piles were surveyed, and less than 8 percent had high levels of root rot. More than 60 percent of Magic Valley piles tested free of root rot.

Strausbaugh said root rot levels in eastern Idaho were too low to warrant surveys.

The root rot observed in the piles was primarily rhizoctonia, although aphanomyces was also present at times, Strausbaugh said.

Rhizoctonia can reduce yields by more than half. Aphanomyces can cause losses in excess of 90 percent, said UI plant pathologist Oliver Neher. They're both soilborne pathogens with a broad range of hosts, including potatoes, beans and corn.

"There is a trend we're seeing of more and more root rot in our piles," Neher said.

Rhizoctonia causes dark spots, dry rot and occasional cracking throughout the root surface. Aphanomyces causes infected stems and roots to turn black and shrivel. Both diseases cause a yellowing of foliage, and infected plants will wilt on hot days.

Rhizoctonia infection penetrates about a half an inch deep within the root, much deeper than aphanomyces, Neher said. Neher added another major problem associated with rhizoctonia is decay caused by secondary bacteria and fungi. Neher said secondary decay produces a sour smell that can easily be detected on a sunny day.

"You can imagine, beets like that aren't going to store well," Neher said.

Aphanomyces, unlike rhizoctonia, requires high soil moisture.

"If you have aphanomyces, please cut back on irrigation," Neher said, stressing that is the simplest control method.

He also suggests lime applications to increase soil pH and micronutrients to help microorganisms outcompete aphanomyces. For rhizoctonia, he suggests applying a 7-inch band of Quadris or Proline over the crowns at the four- to six-week stage.

To combat root rot, growers should also manage weeds, reduce crop residue, control soil compaction and utilize a three- to five-year crop rotation with no corn or beans.

Merle McClain, an American Falls grower, plants rot-resistant beet varieties, such as Holly. Nampa grower Leland Tiegs withholds water from his crops to prevent crusting of his soil, which he has found also helps prevent root rot.

Brian Carlquist, who farms between Burley and Twin Falls, believes his crop rotation has staved off rot.

"We are starting to see more of it show up," Carlquist said. "We are looking for more resistant varieties. Resistant varieties are the most economical control for root rot."

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