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Fighting weed resistance just one of many topics at Ohio Weed University
By Doug Graves
Ohio Correspondent

COLUMBUS, Ohio – There is no graduation ceremony, nor are there certificates to be handed out. But anyone attending the upcoming 2022 Ohio Weed University might feel as though they earned a higher degree of education when it comes to dealing with weeds.
Weed identification, weed control strategies, evaluation of herbicides, local weeds, weed biology, calibrating sprayers and much more will be taught during one-day classes at six locations in Ohio on Feb. 2-3. Participating in the discussion will be weed experts Dr. Mark Loux and Alyssa Essman.
“Common ragweed is more problematic in northwest Ohio, where it has some different resistance issues than in the rest of the state,” Essman said. “Giant ragweed has a lot of biological advantages, in terms of seed size, plant size and especially growth rate. It’s very competitive and can be a real issue year after year. Horseweed, or marestail, also has a number of characteristics that give it an advantage. It can germinate almost any time of the year, and it spreads very easily.”
Essman is a weed science research associate at The Ohio State University and has conducted research looking at the intersection between cover crops and weed control. She has studied the impact of “planting green,” or terminating cover crops after planting soybeans, and the effect on week control and soybean yield. She will address such issues at the upcoming Ohio Weed University.
“There are also some ‘newer’ weeds to Ohio that have been gaining attention,” she said. “Waterhemp and Palmer amaranth are two weeds that farmers need to able to identify and will want to keep out of their fields.”
Loux is a professor at Ohio State who specializes in applied research and extension in the area of weed management in field crops. The general goal of his research and extension programs is to enable producers to make the most effective use of herbicides, minimize herbicide resistance, and reduce herbicide use through manipulation of other agronomic factors.
“As weeds continue to develop resistance to glyphosate and other herbicide chemistries, growers have to modify and diversity their weed management programs,” Loux said. “Diversity is critical to fighting weed resistance. Waterhemp, giant ragweed and common ragweed have very complex life cycles. The idea of a simple solution, regardless of how good a specific herbicide might be, won’t work for long. Resistant weeds are highly adaptable and have long periods of emergence and rapid growth, so they required a complex herbicide program. Any hope of managing resistant weeds requires employing diverse management practices.”
Taking center stage at the Ohio Weed University will be identifying weeds and learning of their characteristics.
According to Loux, weeds can be identified by leaf shape, leaf structure, arrangement of leaves on the stem, flower structure, color, size, arrangements of fruits and seeds, roots, rhizomes, and other underground structures.
Characteristics that are more variable within a species, yet can help identify the weed, include plant height and lateral spread, leaf size, degree of branching, arrangement of branches on the main stem, stem hollowness and leaf or stem coloration.
“Identify weeds with the help of a good field guide, manual or taxonomic key to the agricultural weeds in your region,” Loux said. “Collect a representative specimen or several specimens and examine them closely, including the foliage, stem, flowers, roots and other belowground parts. Growers should familiarize themselves with some of the jargon used in the field guide or key.”
What to apply on weeds will be a large part of this one-day gathering, as will information on spray heads.
“There are certain weeds you spray multiple times, especially with foliar herbicides, and there are a lot of weeds that you don’t,” Loux said. “The weeds being sprayed multiple times are the ones to pay attention to. You have to ask yourself what is the weed, what sites of action are being used and how many times you’re spraying.”
Various Extension educators will be at each location to discuss weed issues along with Loux and Essman.
“If growers are trying to go with a simple approach against weeds, such as loading up with herbicide, resistant weeds won’t respond,” Loux said. “It takes the right systems approach, taking into account resistance to multiple modes of action and weed biology. New technology doesn’t short-cut the need for diverse management practices.”
On Feb. 2, Ohio Weed University will be at the Fayette County Extension office in Fayette County, the Morrow County Extension office in Morrow County and in Roscoe Village in Coshocton County. On Feb. 3, Ohio Weed University will be at the Cherry Fork Community Center in Adams County, Paulding County Extension office in Paulding County and at the Amos Memorial Public Library in Shelby County. The meeting times for each location will be 9 a.m. to 4 p.m.
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