The goal of weed control is to prevent weeds from reaching a growth stage where they can produce seed, giving your crop less competition in the current growing season and reducing the seed bank for future crop years. It’s easy to see the value of weed control when you’re in the middle of growing a crop. It’s a little harder to spend the money on it when there’s no crop in the ground covering those costs.
So, with all the Prevented Planting Acres (PPA) in 2019, growers are faced with many decisions concerning weed control.
Normally, weed control measures end each year when the crop being grown reaches full canopy, which limits light reaching the ground and helps control weed seedlings that might emerge. With no crop, weed control becomes dependent on increased tillage passes or increased contact herbicide applications to manage the weeds until frost or weed emergence halts.
If you had a cover crop on the acres on which you had to take PP, it can be very helpful to your weed control plan, as it provides that established canopy. But for PPA that don’t have a cover crop, tillage and herbicides are excellent ways you can control weeds to prepare for future growing seasons.
Tillage is a great way to control weeds; however, on many acres this may have been difficult or impossible, due to weather. On some PPA, tillage is prohibited because of slope and soil texture. ALSO, tillage can encourage seed germination by stirring up the soil.
Some lucky fields received the planned preplant herbicide before enrolling in the PPA program.
Some applications may have included residual herbicides that helped control grasses and broadleaf weeds. By this time in the season, however, those products have metabolized and are no longer effective.
Burndown herbicides may have been applied without a residual herbicide component and now a second or third flush of weeds may require control.
Herbicide selection has many factors, such as weeds present in the field, length of residual herbicide used, future cropping plan, etc. Whatever herbicide is used, always read and follow label directions.
Positive identification of the weed species present, along with its lifecycle, is critical for selecting the proper herbicide and rate to apply for acceptable weed control. For example, Palmer amaranth emerges from mid-May until the soil freezes in the fall. This weed would require several tillage passes or several burndown herbicide applications.
There are few residual herbicides allowed for extending weed control on PPA. It is questionable if the increased cost of the additional approved residual herbicide would show a positive ROI on a bare soil environment. The final herbicide application of the season may be the best timing to apply residual herbicides.
Cropping plans also determine herbicide selection. Is wheat or rye planned to be drilled this fall? If so, herbicides with long-lasting residual may prevent the wheat from emerging. If planting corn or soybeans next spring, however, an application of a long-lasting residual at this time may keep the field free of most weeds till spring. An example of this would be Valor (flumioxazin) or Fierce (flumioxazin and pyroxasulfone) + Glyphosate + 2,4D.
Some of the more commonly used herbicide program for PPA have been combinations of 2,4D and dicamba for the broadleaves added to glyphosate for grass control. Paraquat with glyphosate has also been used as a burndown product on PPA. There is little to no residual effect from any of these non-selective contact herbicides. However, these herbicides do allow for cover crops, rye or wheat to be planted and grown on the PPA soon after application.
Valor® and Fierce® are registered trademarks of Valent U.S.A. Corporation.