Crop Scouting: Part III - Stay Close to Weeds

Accurately identifying weeds is the first step in successfully managing them.

“Stay close to your friends and closer to your enemies,” the idiom goes. Why? The closer you are to an enemy, the more intimately you will know their capabilities, strengths, weaknesses, and tendencies. Then you can use this knowledge to your advantage.

That makes sense in dealing with weeds – crop pest enemy number one in the minds of many corn and soybean producers.

Accurately identifying weeds is the first step in successfully managing them. ISU Extension weed specialist Bob Hartzler told a group of 75 young crop scouts there’s more than one advantage to being able to identify weeds. “You gain a certain amount of credibility if you can identify weeds,” Hartzler says.  “You’ll find you run into the same weeds over and over—there are really only about two dozen weeds that are problems in Iowa corn and soybean fields.”

Iowa State University publishes a handy Weed Identification Field Guide full of photographs, and concise, helpful descriptions of leaves, ligules, stems, and flowers/fruits differentiating 60 weeds in Iowa.  Hartzler says the pocket weed ID field guide available from ISU includes almost all weeds an Iowa farmer will encounter, and it can be searched very quickly. He prefers the printed guide to phone apps because he can find a weed quickly.

“You want to learn to use a key to systematically rule out similar weeds by traits,” Hartzler says. “A key trait for grasses and the place to begin is the ligule, just above the leaf where it attaches to the plant stem. It could be hairy, membranous, or a ligule could be absent. Foxtails and panicums have a hairy ligule, crabgrass and quackgrass have membranous ligules, and barnyardgrass has no ligule.

It’s also helpful to know something about the life cycle of the weed, so you know when to expect to see it emerging, at full growth, flowering, etc.,” Hartzler says. “If the plant is already large in May, it’s probably a perennial or winter annual,” Hartzler says, “but if it’s an annual like water hemp or foxtail, it will begin germinating in late April or May.”

 Following are photos of one of the weed sessions from the ISU workshop for crop scouts.

Check out parts I and II of the series. 

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