CARBONDALE, Ill. — The historically mild winter of 2011-12 has many farmers considering early spring planting.

But before seeding their first corn hybrids, farmers would be wise to develop risk management tactics for early-season weed management of glyphosate-resistant species, according to professor Bryan G. Young, a weed scientist with Southern Illinois University’s Department of Plant, Soil and Agriculture Systems.

“We often wait too long and never establish early-season control, so we see some escapes,” said Young, who in 2006 joined forces with weed scientists from five other universities to improve the sustainability of weed control in Roundup Ready cropping systems for Monsanto’s “Benchmark Study” of glyphosate resistance management.

“Once a crop comes up we have limited herbicide options and may never gain control. The message is to hit (weeds) when they are small, early in the spring, and keep them down through the use of residual herbicides.”

Young was referencing Monsanto’s “Start Clean, Stay Clean” weed management plan for corn and soybeans. The program calls for farmers to “start clean” with a burndown herbicide or tillage before planting, then applying a Monsanto-approved residual herbicide at the proper Roundup Ready rate.

Upon crop emergence, growers are asked to apply Roundup PowerMax or WeatherMax products before weeds exceed four inches in height in corn or six inches in soybeans.

Implementing and maintaining a proactive weed management plan has never been as critical to crop production as it is right now, according to Young, who has conducted his own study of glyphosate resistance rates in southern Illinois corn and soybean fields for the past three years.

“For presentation at the annual Southern Illinois Fertilizer and Pesticide Conference, in 2009 I began surveying retailers in the southern third of the state. The percentage of acres with glyphosate-resistant waterhemp averaged 12 percent. I did the same survey with the same group in the fall of 2010, and the response was 20 percent. In the fall of 2011 the percentage was 40 percent,” said Young.

“I tell growers, no matter what area they are in, if you rely on glyphosate more than any other single weed control tactic and have had (an increase) in overall resistance to glyphosate, maybe you should expect those problems to double in terms of the area affected every year.”

Though some producers and weed scientists recommend a yearly crop rotation (like no corn after corn) as a way to combat glyphosate resistance, Young’s study – which includes data from some 600 sites – finds no correlation between crop rotation and glyphosate resistance in weeds.

Young said if weeds aren’t managed diligently, resistance to glyphosate could end up robbing some producers of precious yield. “The biggest concern I have with glyphosate-resistant weeds impacting yield is not that we don’t have tactics that we can implement, but it’s how effectively we implement them,” he said.

“If you implement them at the wrong time, in an adverse environment, maybe you are going to impact your yield. We must consistently implement those tactics to prevent yield from being lost.”

Along with waterhemp, marestail and Palmer amaranth are also showing resistance to glyphosate in southern Illinois fields. Although Palmer amaranth has been present in Illinois for some time, it’s becoming more prevalent, according to Young and other Illinois weed scientists, including Aaron Hager of the University of Illinois at Urbana-Champaign.

The Benchmark Study, which began with a telephone survey of 1,200 growers during the winter of 2005-06, wrapped up its field data collection phase in 2010, according to Young.

“It was a five-year study collecting field information. We’re still analyzing data and soil samples to look at the impact of different (management) strategies,” he said.

Some preliminary “summary” reports have been completed for the Benchmark Study, though no timeline has been established for publication of the entire study’s contents. However, those attending the 2012 Integrated Pest Management (IPM) Conference in Memphis from March 27-29 may attend Young’s presentation of the Benchmark Study’s final “economic analysis,” he said.