A friend recently expressed some concern that his traditional early burndown of Harmony Extra and 2,4-D for primrose and other difficult weeds was obsolete. He had heard a lot about Clarity and Ignite and was wondering if these were better.
Harmony Extra and 2,4-D is still a valuable early burndown treatment; however, some new twists are making Clarity and Ignite worth considering. The new twist is horseweed/marestail which is shaking off glyphosate in some cases. If you have horseweed problems, there may be some advantages to the newer herbicides; however, the old standbys still provide very acceptable marestail control.
Clarity is slightly better on horseweed/marestail than 2,4-D. With primrose, it's the opposite and 2,4-D has the edge. Basically, glyphosate-resistant horseweed is just another troublesome burndown weed. It's not that different from the other tough no-till weeds we've fought for years.
Historically, the No. 1 no-till burndown problem has been growers who didn't get their February or March 2,4-D applications out. Horseweed is just one more reason that an early burndown with a growth regulator herbicide is important.
One additional advantage to Clarity is that it can be applied three weeks before planting. Sometimes horseweed germinates in March. When it does, it sidesteps February treatments. If horseweed has been a problem, you may want to skip Harmony and delay 2,4-D until four weeks before planting or switch to Clarity and push for three weeks ahead of planting.
Then again, waiting is dangerous. Again, our number one problem is never getting around to making the early treatment. Whether you use Clarity or 2,4-D, the number one objective is to get it out. Trying to make that application as late as possible should be a distant second.
Ignite is another option. It is a new version of Liberty, which is a non-selective herbicide. (Some of you will remember that Ignite is actually the old name for Liberty.) Ignite has good horseweed activity, along with good activity on many other common weeds. It is a bit stronger than glyphosate on broadleaves, but a bit weaker on grasses and pigweed.
Ignite is being targeted for Liberty Link cotton, but also works in the burndown arena. Ignite will be extremely useful for horseweed in those fields where growers did not get their early 2,4-D or Clarity applied.
If you're having horseweed problems, Clarity, 2,4-D and Ignite are your best options. At the Delta Center we still do a great job with glyphosate, but resistance seems to be spreading rapidly. Clarity or 2,4-D is also needed for a long list of troublesome weeds, including primrose.
However, if you do wind up with horseweed and are short on options, MSMA does a good job — assuming you can catch a good, warm, 80-degree day to do a burndown application. Also, Gramoxone tank-mixed with a herbicide like Caparol, Cotoran or Direx at planting time will do an acceptable, though not quite perfect job. Gramoxone by itself will just “burn the top” and then the horseweed will grow back.
Hopefully this article makes sense. Horseweed brings some new twists to burndown, but it hasn't changed the fundamentals. Clarity and Ignite have utility for horseweed; however, the “old fashioned” early burndown with 2,4-D (and Harmony Extra) is still valid and controls early-germinating horseweed.
Whichever product you chose, just be sure you get that special early application out. One month before planting should be your target, but it's better to be too early than to be forced into using weaker options at planting time. However, Ignite will be a valuable option there.
Andy Kendig is an Extension weed specialist at the University of Missouri Delta Center.