North Carolina State University Extension Weed Specialist Wes Everman is encouraging farmers to think small when it comes to controlling weeds.

No matter what herbicide system they use, Everman emphasizes that weeds must be sprayed when they are four inches tall. Any taller, and you aren’t guaranteed effective control. Moreover, Everman continues to emphasize the need for pre-emergent herbicides and the importance of tank mixes.

At a Nash County Extension grains meeting in Nashville, Feb.15 Everman discussed research conducted by N.C. State last year that examined every herbicide technology used by North Carolina farmers and compared control when weeds were two, four, six and eight inches tall.

Roundup Ready only, PPO only, post-emergence, Liberty Link, Xtend, Enlist, HPPDS, dicamba and 2, 4-D were all examined. Both palmer Amaranth and ragweed control were examined.

“Liberty controlled ragweed at about every size. Dicamba and 2, 4-D did well when weeds were up to six inches tall. Once those weeds got eight inches tall, control was a little big variable by environment. We need to be spraying these when they are four inches tall,” Everman said.

Tank mixes are essential, especially if you don’t have PPO resistance. “If you don’t have two active ingredients in your tank mix, you’re pushing yourself toward resistance and that’s a big concern,” Everman stressed.

Problems with palmer Amaranth are well known, but Everman noted that he actually gets the most phone calls on horseweed than any other weed he works with. “Typically, the call comes in in mid-May and they say ‘Wes, I have horseweed out in my field and it’s about two feet tall, maybe three feet tall. I’m ready to plant tomorrow, what can I do?’” Everman said.

“First, plan better next year.  Second, you’re not going to plant tomorrow because it’s going to be hard to get in the field. There is nothing we can do that’s going to kill a weed today if it’s big and be back in the field tomorrow without some sort of consequences down the road,” he said “We don’t have a cure all on big weeds.”

Everman is emphasizing the importance of burndowns and controlling weeds early. Residuals are also important. Applications need to be made from February to early April to control horseweed before it gets too big. Everman said horseweed needs to be killed before it is eight inches tall, but it must be actively growing.

As he has done at other Extension meetings and field days, Everman again urged farmers to be prepared for resistance. In fact, he cautions that resistance to the dicamba and 2,4-D products may even become an issue if used improperly.

 “We know there are resistance traits in Palmer to herbicides used in these new technologies. It’s just a matter of when we select for the resistance. Right now we don’t have a solution on the back end. We don’t have something new to help us out. This multiple resistance is happening at a faster and faster pace,” he said.

“My worry is that we’ve been so focused on palmer that there might be other weeds creeping along with a little bit of resistance like the multiple-resistant common ragweed. We need to be diligent and realize there are other weeds that could become a problem. I’m seeing more and more sicklepod and more and more cocklebur coming along. I’m not saying there is resistance, but we’re definitely seeing more of them of them in the ditches and the fields. Be aware.”