Timely Corn and Soybean Weed Control Recommendations

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

There have been a few calls about late season weed control in corn. Our HPPD herbicides (Callisto, Laudis, Capreno, Impact, Armezon, Shieldex) all need some atrazine with them for control and are not very effective by themselves on weeds over 5 to 6 inches. At this stage most of the corn is too tall for atrazine applications. Other options include Status or Diflexx. Both of these include dicamba, so be cautious about where and when you apply them (hot temperatures or sensitive crops and plants nearby). But if you are in a situation where dicamba is an option, both Status and Diflexx contain a safener so there is less twisting and leaning of the corn (twisting and leaning are not eliminated but less severe). Diflexx has to be applied before corn is 36 inch tall or V6 (which occurs first); Status needs to be applied before corn is 36 inch tall or V10.

Temperatures have climbed above 90 degrees the past few days and with the recent rain, Palmer amaranth has really started the rapid growth phase. If you have fields infested with Palmer amaranth or if Palmer amaranth is in the vicinity, get out to those fields and check on Palmer amaranth and get your postemergence herbicides applied before plants are 3-inches tall. Typically, this is no later than 4 weeks after the preemergence herbicides was applied. If you have Palmer amaranth, postemergence sprays should include a herbicide that provides residual control (Reflex, Anthem, Zidua, Dual, Warrant). Also, be aware if soybeans were planted in 30-inch rows you may need a second postemergence application due to delay in soybean canopy closure.