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by | May 11, 2018

The biggest reason for poor marestail control is treating large plants. Marestail more than 4 to 5 inches tall is difficult to control, regardless of the herbicide used. (Photo courtesy Ohio State University)

Growers should keep up with advancements in weed management or risk the consequences on their fields, agricultural educators said last week.
Whether it’s complacency with herbicide rotation or properly treating fields after harvest, farmers can inadvertently grant noxious weeds entrée to their cropland.
“Sometimes some folks can get stuck in a rut using the same (herbicide) over and over again,” said Andrew Kness, a University of Maryland Extension agent in Harford County. “A lot of education for moving forward is trying to harp on the point that you need to rotate chemistries (to prevent resistance).”
For instance, Palmer amaranth, an aggressive pigweed, has quickly become a frequent source of aggravation for farmers since it arrived in the Delmarva region after migrating from its native Southwest across the southeastern Cottonbelt and into the Mid-Atlantic.
It can quickly establish a presence in grain and vegetable fields, growing up to two to three inches per day with each plant producing up to half a million seeds.
Understanding the likelihood of a weed like Palmer amaranth taking hold on your fields is important, said Lane Heimer, a weed control expert at the Maryland Department of Agriculture.
“They need to be familiar with their fields and scout more often, certainly,” he said. “Prevention is a big thing.”
It’s important to attack the plant at the proper growth stage — before it reaches 4 to 6 inches tall, several agronomists said. Other weeds, such as marestail, water hemp and common ragweed often bedevil Delmarva fields, and it can be costly for farmers, particularly now, when commodity prices are low. Entrenched weeds can cost a farmer up to $30 an acre when he has to spray extra to fight them, Heimer said.
Maryland farmers may eventually get some assistance in the fight against Palmer amaranth from the state government. Maryland has decided to study the problem in the fall to determine the weed’s cost to the agricultural industry and what can be done to combat it (and how much that effort will cost taxpayers). A report is due back to the General Assembly late next year.
Delaware has already recognized it on its noxious weed list.
Soybean growers also have a new advantage, Kness said — dicamba-tolerant seeds marketed under the trade name Roundup Ready 2 Xtend, which should be particularly useful against Palmer and marestail. Maryland Extension officials have been advising growers over the last year about the advantages and risks — such as drift on neighboring, non-tolerant fields — to using the herbicide as it becomes more popular in the Mid-Atlantic.
“That’s a new tool in their toolbox that they didn’t have before,” he said.
Although the large majority of farmers do a good job monitoring and treating their fields for fields, growers should consult local Extension agents or agronomists for new developments in weed management.
“You got guys that, as soon as the newest things come out, they jump on it,” said Todd Davis, a noxious weed specialist at the Delaware Department of Agriculture. “The ones that are lagging behind are the ones we’re having the most trouble with in weed management.”

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