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Crop Field Scouting Turns Up More than Pests

Crop Field Scouting Turns Up More than Pests

Joplin tornado debris, bacteria and armyworms found in southwest Missouri corn and wheat fields.

The biggest surprise in wheat and cornfields in southwest Missouri last week was debris from the Joplin tornado.

Tim Schnakenberg scouted corn and wheat fields in Dade and Barton counties – a weekly spring routine for the University of Missouri Extension agronomy specialist. "It was sobering because I found debris like miscellaneous papers, a utility bill, a canceled check, cards, a photo and building materials from Joplin," he says.

The fields were also saturated from recent rains and the corn was in need of sunshine and heat. Much of the corn in this region of southwest Missouri had been replanted and the older corn was small and undeveloped for its age. Corn ranged from just spiking (VE) to about the V5 stage. 

"Color of the leaves was surprisingly good for the amount of rainfall we have had. Leaves of the older corn still showed some signs of the hail from a week or two ago," Schnakenberg notes.

The most obvious issue found on older stage corn was whitish oval spots on the leaves, he reported. These spots had no margin, indicating that it is possibly bacteria called Holcus leaf spot.  This occurs occasionally following a hailstorm or strong windstorm that brings in the bacteria for infection. 

"This condition is considered to be fairly benign to the plant since it does not produce fruiting structures in the lesions following infection.  For this reason it is believed that the plant should outgrow the problem with time once growing conditions improve," Schnakenberg says.

Armyworms in check

Insect activity appears to be minimal, although reports of more significant feeding have come from areas in Stone and Barry counties. Signs of true armyworm feeding were found this week but nothing significant in number.

"This can change quickly with warmer, dryer growing conditions, so farmers should continue watching the crop for this development," Schnakenberg says.

The threshold for treatment of true armyworms in small corn is when 25% or more of the plants are being damaged. The true armyworms that Schnakenberg found were still small, but this can change quickly with warmer weather. Growers should scout for armyworm activity including leaf feeding higher in the canopy and clipped heads as harvest gets closer.

The threshold for treatment of armyworms is when four or more half-grown or larger worms are seen per square foot and before two to three percent of the heads are cut from the stems.

"Scouting is most successfully achieved at dusk or dawn since they do most of their feeding at night. They often remain in the plant debris during the day," the agronomist says.

Wheat field progress

Wheat fields were developing slowly and are at the watery ripe kernel stage of development. The crop will very quickly be in the milk stage.

"The most pronounced symptoms found in many fields were the purple and yellow flag leaves that were due to the Barley Yellow Dwarf virus.  This virus was most likely infected by aphids last fall," Schnakenberg says.

"Highly productive fields should be scouted in the late fall for aphid activity.  Treatment at key times may help to prevent this virus infection. There is nothing that can be done to the crop at this stage."

Some fields showed infection from loose smut, showing the signs of black sooty mold on the heads.  Seed treatment at planting can guard against some of this infection. "Diseases were developing rapidly due to recent weather conditions but it is past the time to treat for these problems. The primary disease noted was Septoria leaf blotch which was at least half way up the canopy in some fields," Schnakenberg says.

Fields that had been treated with a fungicide were in better shape. For example, in the treated fields, Schnakenberg saw little disease symptoms in the head as well as no Fusarium head scab. 

Source: University of Missouri Southwest News Service

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