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Scout: Eyespot heavy in central Iowa corn

By Staff | Jul 31, 2009

Crop consultant Hal Tucker, owner of Tucker Consulting Inc., of Storm Lake, examines a corn plant last week in a field southwest of Albert City in Clay County. The leaves in this corn-on-corn field is showing advanced eyespot infection and was scheduled for fungicide treatment this week.

FONDA – A Storm Lake-area crop consultant and an Iowa State University plant pathologist are in agreement that corn eyespot has developed in alarming quantities within central Iowa.

Hal Tucker, who owns Tucker Consultanting Inc., showed Farm News two fields within Pocahontas County last week that were showing signs that eyespot could be in great enough quantities to not only rob producers of yield this fall, but could also cause standability problems by weakening stalks.

One of the fields Tucker pointed to was corn following soybeans slightly north of Fonda. The second field was corn following corn located southwest of Albert City. Although it’s still not certain, researchers believe that eyespot can reduce yields by upward to four percent.

Plant pathologist Allison Robertson said that although she is usually hesitant to recommend spraying fungicides, the widespread, intense infections she has witnessed in the Fort Dodge/central Iowa area “makes me a little bit nervous. If you can afford to spray and if you want to, go ahead and treat.”

The treatment threshold is is still not certain, Tucker said. If the infection is on V12, the ear leaf at tasseling, with significant lesions on corn that is susceptible, then spraying could be recommended. However, he said, it would be more worthwhile to look at planting resistent (corn) varieties.

This leaf shows extensive eyespot fungus infection. Each of the lesions contain inoculum spores that will be released at the next rain expected earlier this week and would affect other new leaves that will have grown since the last rain. A crop consultant and an Iowa State University plant pathologist agreed this field was bad enough to treat before pollination was complete. The field was scheduled for treatment this week.

“But you can see here that it’s on the ear leaf and keeps going up,” Tucker said, examining one plant in the Fonda-area field. The Albert City-area field was at the same stage of infection a week earlier and has gotten worse since then. “About five percent of the plant material is infected,” Tucker said.

Tucker indicated where the field near Fonda showed two separate hybrid corn genetics were equally infected with eyespot. The fungus was evident on the ear leaves, as well as climbing to leaves higher on the stalk. Even though the corn residue in that field was two years old, the fungus survived, most likely due to reduced tillage practices, Tucker noted. As a result of last fall’s lack of tillage, along with this season’s early cool, wet weather, the inoculum fungus got an early start and quickly spread.

Looking at the sporadic patterns on some higher leaves, he noted, “Some of this probably blew into this field.”

Tucker said he first noticed the heavy concentration of eyespot a month ago. The infected corn was at V8 and V9 stages. On July 10, he showed the widespread infections to Robertson. “She said, ‘this is bad,'” Tucker said.

The disease gets its name for the lesions that appear to look like an eye a light-colored spot with a darker ring around it. The lesions, Tucker said, “is the inoculum incubating.” The lesions also inhibit the leaf’s ability to allow the plant to breathe, which will stress the overall plant for filling ears and could lead to lodging this fall if stalks weaken from it.

The spores are released through moisture, whether through rain, heavy dew or plants in fields, which are prone to develop fog. Tucker guessed that there have been several infections caused by repeated wet, cool weather patterns throughout spring and early summer. It takes about 10 days for lesions to appear after spores land on leaves.

“If we get the cool temperatures and the wet weather this week that they say we will, that’s eyespot weather,” Tucker said.

The Albert City-area field was in worse condition, with eyespot more advanced and spraying scheduled for this week. Normally, he said he’d recommend waiting until pollination is complete. “But this field is a no-brainer. We’re not going to wait for this one.”

The corn-on-corn acres were more infected, Tucker said, because there was more residue on the ground at planting. Last year’s corn may have been infected to a lesser degree, but the spores were readily available, with infections starting fairly quickly after emergence.

“I’ve never seen it this bad, this early,” Tucker said who’s been consulting for many years in two different states.

Robertson said she has not heard that eyespot was evident at these levels anywhere else in the state. “Mostly in the Fort Dodge and Central Iowa pocket,” she noted.

Contact Larry Kershner at (515) 573-2141, Ext. 453, or by e-mail at kersh@farm-news.com.

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