Pathologist predicts less stripe rust, more headblight in Idaho
By JOHN O'CONNELL
University of Idaho Extension cereals pathologist Juliet Marshall predicts Idaho grain growers should have little trouble with stripe rust this season, but it could be another bad year for Fusarium headblight.
Marshall said the fungus that causes stripe rust -- which forms rows of yellow-orange pustules on leaves that release spores that get blown with the wind -- doesn't tolerate temperatures below 20 degrees.
"We had some pretty cold temperatures in January and February this year," Marshall said, adding a hot and dry summer also shriveled plant material that could have carried spores into the next crop. "I believe if stripe rust comes, it will be later in the season and mostly affect late-maturing spring grain."
Growers should have ample warning to spray if stripe rust blows in from Oregon or Washington, where disease pressure should be moderate. Idaho's last bad stripe rust season was 2011.
However, headblight has been on the rise in Idaho. Headblight creates vomitoxins in grain, which induce vomiting in humans and swine and can be harmful to cattle at higher concentrations. Marshall said wheat with above 5 parts per million of vomitoxins is at risk of rejection. In lesser amounts, it may be mixed with clean grain to levels below 1 part per million.
Last season, loads were rejected for vomitoxins from Ashton through Magic Valley, Marshall said. In some fields, she found 30-35 percent of grain was infected. She believes a steady increase in corn acreage has exacerbated the problem. While the vast majority of the region's headblight was once caused by the fungus species Fusarium culmorum, most infections are now attributed to Fusarium graminearum, a more aggressive strain that thrives on corn.
Marshall speculates the regional climate is becoming more humid, helping headblight.
"We need to find some research money to investigate why it is increasing," Marshall said.
Headblight infects grain at the flowering stage, which occurs in Idaho spring grains near the third week of June. She advises grain growers to spray with a triazole-based fungicide at flowering for headblight protection. Temperatures are usually too cool for headblight when winter grains flower.
"Very few growers regularly spray spring grain at flowering with fungicide," Marshall said.
Few headblight-resistant varieties have been developed, but Marshall is optimistic about a new high-yielding soft white spring wheat, UI Stone, moderately resistant to both headblight and tolerant to cereal cyst nematode.
Mark Morgan, a crop adviser with Simplot Grower Solutions, said headblight posed less of a problem in the Blackfoot area last season because a few growers moved their corn fields further south.
"The more corn, the more (headblight) you see," Morgan said.
Declo grower Mark Darrington anticipates unmet demand will continue to drive corn acreage growth, but he doubts growers will spray at flowering until they experience a problem with headblight.
Based on customer meetings, Jim Vandecoevering, technical service representative with BASF in Meridian, anticipates triazole sales for controlling headblight will increase this season.
"I think they're just starting (headblight applications) because it's basically a new disease for us based on our corn acres," he said.