Harvesting first cutting alfalfa and then no-tilling corn can be challenging and certainly carries some risk, a Penn State University agronomist says.
There are primarily two challenges, says weed scientist Bill Curran. First, getting acceptable control of alfalfa after first cutting requires some planning, and second, even with acceptable control, the dying alfalfa may impact corn yield.
"Glyphosate may be applied to declining stands to help control the legumes and other plant species," Curran says. "This can be particularly helpful for control of perennial grasses including quackgrass or forage species such as orchardgrass."
If the crop is to be harvested or grazed by livestock, Curran says you can use up to 1.5 pounds of active ingredient per acre (2 quarts of a 3-pound ae/gal product) in alfalfa. The minimum interval between application and harvest is 36 hours and by 5 days after application you are losing forage quality.
"One of the biggest challenges to making this work is having the right weather conditions to allow timely harvest," Curran says. "This treatment will also not provide sufficient control of the alfalfa, but it will suppress it and potentially allow for more timely control and reduced competition in no-till corn. In no-till corn, a Post application should be made to control the alfalfa regrowth."
Curran says the plant growth regulator herbicides (2,4–D, dicamba, clopyralid — Stinger and Hornet, as well Status) should help control alfalfa post-emergence in corn. In Roundup Ready corn, glyphosate can also help suppress the legume and a growth regulator herbicide could be tank-mixed with the glyphosate.
An alternative approach is to delay corn planting, making sure there is adequate regrowth before making the herbicide application. A combination of 2,4–D and dicamba (Banvel or Clarity) is probably the most consistent for control of alfalfa, Curran adds.
"Glyphosate will add some alfalfa control and is a definite must if perennial grasses are present," he says. "Of course the greatest risk is not waiting and no-tilling corn as soon as possible after harvest. This is a bit risky, but can be successful if good fortune is on your side."
Planting Roundup Ready corn and a “well-timed” application of a dicamba-based product (Banvel, Clarity, or Status) or perhaps a clopyralid-containing product (Stinger or Hornet) tank-mixed with glyphosate could work, Curran says. Use the full rate of Status or Hornet or at least 12 ounces of Banvel or Clarity. Better yet, he says you should wait 10 to 15 days after harvest before spraying the alfalfa (minimum of 6 inches of regrowth) and then plant corn.
"Unfortunately, none of these approaches will prevent the negative effects of a dry spell early in the growing season that can be devastating to corn planted after first cutting hay. Here’s where that good fortune comes in handy again," Curran says.