Planning A Herbicide Program

Tyler Mahrer
Agtegra Agronomist

The primary goal of a herbicide program is to select different chemistries to control the tough-to-kill weeds on the farm to increase ROI. Choosing the right herbicides and the most ideal timing to apply them is a complicated decision, but here are some tips to help you think it through.

Evaluate What Weeds You Have
Step one to having a clean field at harvest is having an idea which weeds are present in that field before the season starts. We’re not saying you need to know every weed that’s ever been in your field, but if a certain part of your farm has a known kochia or waterhemp issue, these are things to note before selecting a herbicide. Different pre-emerge chemicals work better in different situations and environments, so selecting the correct herbicide is half the battle.

Focus on the Beginning of the Season
Use a “Start Clean, Stay Clean” approach. A clean field from an effective pre-emerge with an effective burn down, if needed, is essential to young plant development in both corn and soybeans, but is also important to thinning out weed pressure for post-emerge application. This system approach also helps to protect newer weed control platforms from developing resistant weeds. In less than 25 years, we have gone from weeds dying from small amounts of glyphosate to full-blown resistance at 2X and 3X rates.

Consider a Second Pass
No pre-emerge chemical program will be spot free, especially with some of the fields that have high weed pressure from resistance issues. It is important to scout early and often to catch the first flush of weeds—typically within 3-6 weeks of planting, depending on rainfall, weed physiology and temperatures. Once this first flush is up, it is important to recognize several factors that will determine your level of weed control from in-season application. Just a few of these factors are timing/weed size, which chemicals to use, how much weed pressure, canopy coverage and other simple things like, does my chemical need 10 gallons of water, or will I benefit by spraying 15-20 gallons? Water is the cheapest ingredient you can throw in a sprayer when spraying contact herbicides.

Using a second pass also comes with the option for an in-season residual. An in-season residual can be an effective way to avoid having to come back for a third pass for later emerging weeds like lambsquarters and waterhemp, as well as help in controlling weeds in wider row crops that may not canopy until later in the summer. All these factors can add up to how many weeds and how many bushels are out in the field at harvest.