Understand the Correct Timing Window for Your Herbicide Program for Best Control
Application of postemergence herbicides is an important weed management tool in both corn and soybeans. Making sure to correctly time this application can easily make or break your weed control program. Here are some reminders to help make the correct decisions about herbicide application. Remember to always read and follow the label for a given product and when tank mixing always follow the most restrictive label.
Crop Stage
Many products include a restriction for crop growth stage for crop safety. Corn height is determined by measuring from the soil surface to the arch of the uppermost leaf that is more than 50% emerged. For soybeans, The V stages are defined by the number of trifoliate leaves that have developed (unrolled) on the main stem, not the branches.
Weeds Controlled and Weed Height
Herbicide labels have a two part weed list 1) which weeds are controlled and 2) the maximum height those weeds can be for control to still be effective. Make sure your problem weeds are covered by your herbicide program and monitor their size with continual scouting. Smaller weeds are almost always easier to control. Remember that a 4 inch tall weed is slightly shorter than a pop can – not almost to your knee!
Overlap Residual Products
Most postemergence programs today include one or more products that offer residual control. This can help to fight late emerging weeds like waterhemp. We get the most bang out of these products when they are applied to bare soil compared to already emerged weeds. Aim to ‘overlap’ or apply these products before your preemergence herbicide has broken. Many companies suggest to apply their postemergence products around 28 days after planting. It comes quickly!
Respect the Rainfast
We all try to squeeze in that last field before rain moves in but always check a products rainfast. Rainfast is the minimum period needed inbetween application and a rainfall event for control to be effective. These vary significantly from 30 minutes to 24 hours depending on the herbicide product. This information can always be found within the herbicide’s label.
Wind Direction
Growers spraying dicamba are not the only ones who need to know the wind direction and speed. With the increasing adoption of Liberty Link and conventional seed, always check with your neighbors to see what is across the fence before hand. Determine what direction you need the wind to be out of for each find before hand to help make decisions more quickly.