The threat of weeds has amplified in the last 25 years, said Dr. Kevin Bradley, state weed science specialist. The proliferation of Roundup-ready crops, plants developed use with the Glyphosate herbicide, has created a new problem.
Glyphosate-resistant weeds have since surfaced that now seriously challenge farmers. The worst of these are two types of pigweed: waterhemp, which grows in southwest Missouri, and the large-stalked Palmer pigweed.
Bradley said the key to fighting weeds is knowing the strengths and weaknesses of the enemy. Waterhemp is vulnerable to combinations of sprays if hit below the height of four inches. Its seeds will only grow from shallow soil. Seeds only live for around five years, while most other seeds last as long as 20 years, and some as long as 40 years.
Palmer pigweed seeds seem to have infiltrated commercial flower plant seed supplies and even spread in animal seed
As preventative strategies, Bradley recommended planting in weed-free fields; reducing the soil seed bank, rather than spreading weed seeds with combines; using uncommon strategies such as reducing the space between rows or using cover crops to smother weeds.
"You can't go out [and beat these weeds] with Glyphosate or more Glyphosate," Bradley said. "The good news is we have tons of good combinations of products that will work. But it's going to get more complex, not simpler."
Details on recommended strategies are available on-line at http://weedscience.missouri.edu.
More persistent weeds
Agronomy specialist Tim Schnakenberg, who helped to organize the conference, continued Bradley's theme by discussing five major weeds that regularly generate inquiries: thistles, Johnsongrass, poison hemlock, spotted knapweed and plantains. Schnakenberg said imported hay can bring come with a big supply of strange weeds.
"If you're seeing newer weeds, do something the first year," Schnakenberg said. "You'll get a much greater benefit."
Over-grazing and seasonal droughts have created openings where weeds take hold. Schnakenberg said he fears many fields will be filled with thistles in 2013.
Thistles can produce 10,000 seeds per plant that live for up to seven years. Hay infested with spotted knapweed can enable the weed to spread all over a pasture, even overcoming fescue in 10 years. Poison hemlock can overwhelm fescue even faster than Johnsongrass, which spreads by roots and seeds. The Buckhorn plantain, an increasing problem in droughts, takes hold in pastures and "is not going away" once established.
Spraying at the right time and aggressively fighting the weeds are the only strategies that succeed, Schnakenberg stressed.
Eldon Cole, extension livestock specialist who served as master of ceremonies with Schnakenberg, announced copies of the "Little Red Book" for keeping livestock records, were again available.
A near capacity crowd attended the conference. A steak dinner was provided by the Mt. Vernon Chamber of Commerce, in cooperation with the Southwest Missouri Cattlemen's Association, Mid-Missouri Bank of Mt. Vernon and Ozark Electric Cooperative.