As corn and soybean planting approaches, a few best management practices for pre-plant burndown herbicide programs should be considered.
John Wallace, a Penn State Extension weed management specialist, says burndown programs are most successful when applied in weather conditions that ensure targeted weeds and cover crops are actively growing (day temperatures above 55 degrees, and above 40 degrees at night).
Take time to review herbicide labels to identify potential tank-mix antagonism issues, preplant restrictions on product labels to minimize risk of crop injury, and harvest intervals on product labels when terminating forage crops.
Here are a few additional details.
First, let’s consider nonselective burndown products (glyphosate and paraquat).
Apply glyphosate at a rate of 0.75 to 1.13 pounds per acid equivalent with appropriate adjuvants (surfactant plus ammonium sulfate) and in 10 to 20 gallons of liquid carrier per acre.
Carriers may include liquid nitrogen fertilizer or clear liquid complete analysis fertilizer. Avoid use of suspension-type liquid fertilizers as a carrier. Consider using the 1.13-pound rate when tank-mixing with nitrogen carriers or residual herbicides.
Paraquat (Gramoxone SL) can be used as an alternative to glyphosate for preplant burndown applications.
Apply paraquat at 2 to 4 pints per acre when using a 2-pound formulation, or 1.3 to 2.7 pints per acre if using a 3-pound formulation.
To optimize control with paraquat, use a high carrier volume (20 gallons per acre) and flat fan nozzle tips to improve coverage. Inclusion of a non-ionic surfactant, a triazine herbicide (atrazine, metribuzin), or UAN as a partial carrier can improve paraquat activity.
Commonly used broadleaf products include 2,4-D and dicamba.
2,4-D ester or dicamba can be tank-mixed with glyphosate or paraquat to improve control of certain broadleaf weeds and cover crops.
Dicamba is generally a better product for control of leguminous cover crops, and 2,4-D ester is a better product for controlling dandelion and mustard species.
Before corn, 2,4-D ester (LVE) can be applied at 1 pint per acre seven to 14 days preplant, or three to five days after planting to improve crop safety.
Dicamba can be applied at 1 pint per acre on medium and fine textured soils with at least 2.5% organic matter, and can also be tank-mixed with 2,4-D when applied seven to 14 days pre-plant.
Additional safety is achieved by planting corn 1 ½ inches deep to minimize the risk of these products coming in direct contact with corn seed in the furrow.
Before soybean, 2,4-D and dicamba products can also be used to improve control of certain broadleaf weeds and cover crops, but preplant restrictions will vary depending on soybean seed traits.
If using non-GMO or Roundup Ready soybeans, 2,4-D ester (LVE) should be applied 30 days preplant at a 2 pint rate (1 pound of acid equivalent per acre) and seven days pre-plant at a 1 pt rate (0.5 pounds of acid equivalent per acre).
Dicamba products such as Clarity should be applied 28 days preplant at a 1 pint rate (0.5 pounds of acid equivalent per acre) and 14 days preplant at a 0.5 pint rate (0.25 pounds of acid equivalent per acre).
Xtend and XtendFlex soybean traits permit use of three dicamba products (XtendiMax, Engenia and Tavium) at standard labeled rates (0.5 pounds of acid equivalent per acre) without preplant restrictions.
Enlist E3 soybean traits permit use of two 2,4-D choline products (Enlist One, Enlist Duo) at the standard labeled rate (1 pound of acid equivalent per acre) without preplant restrictions.
When terminating winter grains harvested for spring forage, several factors should be considered.
Chopping cereal rye or triticale prior to flowering is generally not an effective method of termination.
Previous Penn State field trials have demonstrated that chopping rye at the late boot stage can result in up to 80% regrowth, and chopping at the mid-heading stage can result in up to 50% regrowth.
Spraying cereal rye with common burndown products (glyphosate, paraquat) prior to ryelage harvest is illegal. Consequently, termination of cereal rye that has been harvested for forage is best managed with postharvest herbicide applications.
Glyphosate (1.13 pounds of acid equivalent per acre) is generally a more effective burndown option than contact herbicides like paraquat for post-harvest termination of cereal rye.
It is likely not necessary to delay termination after harvest to allow for regrowth when using glyphosate, as long as the harvest height results in enough green leaf tissue at the base of plants to absorb the systemic herbicide, and weather conditions are optimal for uptake and translocation.