Weeds Take A Back Seat

Heat, Drought Overshadow Weed Control Issues Last Year

BELLEVILLE, ILL.

   Early last year it seemed the biggest challenge would be weed management, but as the year progressed, Dr. Bryan Young, weed scientist at Southern Illinois University, found the heat and drought stress was even more compelling.

   “Certainly those two factors, the heat stress as well as the drought stress, has impacted weed control,” he said. “In some cases initially it hurt our weed control in that we didn’t get rainfall for activation of our residual herbicide; and then also those hot dry conditions didn’t allow our post emergence herbicides to reach their optimum activity. But what ultimately happened to many of those weeds that survived the post emergence herbicides fell victim to the drought and had less opportunity for robust regrowth. The weeds certainly didn’t thrive compared to if we had gotten high rainfall conditions and good soil moisture. That way they could have survived better.

   “The fact that some of the weeds did die off and then the crop canopy took over a little bit has resulted in weed control looking better than at the same point in 2011; but it’s for a bad reason and that would be the heat and the drought.”

   Other problems last year for weed management, included a greater frequency of glyphosate resistance and resistance to PPO inhibiting herbicides in the species waterhemp.

   “We had been keeping an eye out for that as well,” Young said. “We continued to have challenges with glyphosate resistant horseweed or marestail and we found more populations and questions about whether we have more of this glyphosate resistant Palmer amaranth. Those are things that we continue to educate about, try to look at Palmer amaranth identification versus waterhemp, and what the main differences are between the two and why that is important. They look similar and control measures are somewhat the same, but Palmer being more competitive, we need to be more aggressive in terms of application timing; make sure we have those residual herbicides in there because Palmer will be able to choke out some waterhemp infestations which is not good news. We have these different tools, herbicide traits we can look for in the future, especially the soybeans like 2-4,D, dicamba and LibertyLink systems. However, these systems all rely on a well-conceived and implemented management system involving residual herbicides and several herbicide modes of action.”

   Young also spoke about soil residual herbicides. You can use these residual herbicides in any seed trait you pick and that’s important. No matter what seed you choose you can rely on these residual herbicides.

   “To boil all this down, we need to be sure that we’re managing weeds with residual herbicides, making timely applications, scouting fields, and making sure that our herbicides are working,” he said. “We also need to make sure that we don’t have any new species introduced, such as the Palmer amaranth, that we haven’t had before as a problematic weed; weed seeds are being introduced across our farms and not just from field to field but county to county. When we move livestock feed, when we move equipment we just have to be managing weeds, scouting for weeds to make sure we’re as profitable and successful in the future.” Δ

BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower

Dr. Bryan Young, weed scientist at Southern Illinois University, found the heat and drought stress added to the 2012 weed control challenge.

Photo by John LaRose Jr.