Production Blog

DECATUR, Ill. (DTN) -- My family is great for sayings. One of my grandmother's favorites is: "The difference between a flower and a weed is judgment."

My grandmother will be 103 years wise this August and her old adage kept whispering to me this spring as I spotted roadside daffodils lining farm fields thickly carpeted with purple deadnettle, henbit and chickweed.

The fields and gardens of my youth were classrooms for learning the important differences between pest species. Unfortunately, we let a lot of those lessons fall by the wayside as herbicide-resistant technologies came on the scene.

There's no question that the miracles of science made our life easier. It's also human nature to keep using a product when it is working -- particularly if it is inexpensive. However, Mother Nature keeps reminding us it has the final say. Weeds exhibiting resistance to herbicide are once again teaching us the necessity of getting back to basics and the importance of adding judgment back to our weed management tactics.

The need to know the difference between weeds such as henbit and waterhemp is a big deal when assessing risk, according to Kevin Bradley, University of Missouri weed scientist.

"Delayed planting has left big mats of winter annual weeds out there," Bradley told DTN in a phone interview. "Purple deadnettle and henbit will senesce and die back naturally.

"Targeting winter annuals right now is mostly revenge killing, but we do need to start clean and allow the planters to get the seed in the ground," he said. "As I walk through fields matted with these weeds, I'm finding they are mature and have already shed seed."

What he sees as more of a threat now is the fact that summer annual weeds, such as waterhemp, are already appearing in fields. Understanding that waterhemp produces on average 300,000 seeds per plant, grows an inch and a half a day during the height of the growing season, and has evolved resistance to just about every herbicide ever sprayed means getting those first flushes controlled is critical.

Still, Bradley said growers continue to depend too heavily on glyphosate only in burndown applications. "If they would just add some Sharpen or 2,4-D, it would make such a big difference," he said.

"The other problem I see is growers have this mindset of wanting to cut rates when adding things like 2,4-D. They don't want to wait the required seven days to plant in this situation, which is required by the 2,4-D label," Bradley explained. He noted that growers utilizing tank mixes of multiple sites of action and overlapping residual applications are having the best results controlling waterhemp.

Unfortunately, delayed planting seasons, like the one being experienced this year, compress already complex decisions, said University of Illinois weed scientist Aaron Hager. "Ultimately, whatever weed is out there is competitive, regardless of species.

"There are no good things weeds do to a crop," Hager told DTN in a phone interview. "However, species identification is becoming increasingly important, particularly as we see more aggressive weeds in the landscape."

Waterhemp, while worrisome, is a mild relative of Palmer amaranth (also known as Palmer pigweed or pigweed). "The difference in growth rate, how competitive it is and the very narrow window available to control Palmer before it gains a foothold makes identification critical," Hager said.

Confirmed cases of herbicide-resistant Palmer amaranth in more northerly regions grew last year. Weed scientists are asking growers to report suspected sightings this spring and summer.

Weed resistance is real, Hager stated. It's time to understand weed biology and use educated steps to best defend your farm.

"Understanding that these are biological systems and there will always be things that evolve and happen within it is a first step," he noted. "There is no one size-fits-all solution. It's up to each grower to determine how they will manage the risk."

Pamela Smith can be reached at Pamela.smith@telventdtn.com

(AG)

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