Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
As wheat harvest starts to kick into high gear, planting double-cropped soybeans is right around the corner. Even if the wheat field appears to be clean, there is likely to be small weeds that are ready to grow rapidly once they get more sunlight. So it’s important to use a good burndown herbicide to control emerged weeds.
Glyphosate is the best option, and even in situations with glyphosate-resistant weeds, it will control a number of species. Where glyphosate-resistant horseweed, Palmer amaranth, or common ragweed are present you will need something in addition to glyphosate to control these plants. Glyphosate plus Liberty has been a pretty good treatment for burndown weeds prior to planting double-cropped soybeans in the past few years. While some of the newly released soybean traits (Xtend and Enlist soybeans) may be helpful from a control standpoint, they are only appropriate in certain situations due to off-target movement and proximity of susceptible plants. We have found the glyphosate plus Liberty (or other glufosinate formulations) combination to work very well in many situations but just a few things to keep in mind.
- Liberty needs good spray coverage to maximize effectiveness, including when its tankmixed with glyphosate. A minimum of 20 gallons per acre should be used with medium to coarse spray droplets.
- Liberty works best with full sunlight; spraying in the morning or evening or during heavy cloud cover can reduce effectiveness.
- I will occasionally see poor control of fall panicum with this combination. I am assuming the Liberty is interfering with glyphosate from providing complete control. This is more likely to occur with large fall panicum plants. I have not seen this reduction of control with other annual weed species, but giant foxtail and large crabgrass are the only other grasses in most of my trials. I suspect an increase in glyphosate rate would help reduce the likelihood of this happening, but I have not tested this.
- This combination will not provide residual control so in fields with Palmer amaranth it is important to include a residual herbicide.