By Darren Hefty

Let’s face it.  Roundup is by far the best herbicide ever created, but due to resistant weeds it’s not the right choice for burndown in some situations, at least as a stand-alone choice.  Let’s start from scratch, building a burndown program with a broad-spectrum base product and possibly some add-ons for Roundup or one of the other base herbicides.

Base Products

You know about Roundup and the job it can do.  There are two key base products that can take the place of Roundup in your burndown program if Roundup is no longer effective for you:  Liberty or Gramoxone.  Neither one of them is just like Roundup.  Neither has the systemic root-killing power of Roundup.  However, they can each provide good knockdown of weeds, including Roundup-resistant ones.

GRAMOXONE – First of all, if you haven’t used Gramoxone before, you need to be aware of the safety of the product.  It is not nearly as safe for you to use and be exposed to as Roundup.  A cab on the sprayer and personal protective equipment are a must.  That said, Gramoxone is a highly effective burndown product and quite possibly the fastest-working herbicide you’ll use.

Gramoxone is a Group 22 herbicide that kills weeds as a photosynthesis inhibitor.  It is non-selective and will burndown both broadleaf and grass weeds. To heat up the spray solution, adding 1 gallon of crop oil or methylated seed oil per 100 gallons of solution is a must.

LIBERTY – The other base product is Liberty.  Using it as a burndown is not cheap, but in terms of weed control it’s a pretty good option that is non-selective, killing both grasses and broadleaves.  The safety of the product is good, and we haven’t seen the drift issues with Liberty like we have with Roundup.

The Downside of Alternatives

So if you’re thinking, “These products don’t sound so bad.  Why wasn’t I using them in the first place?”  Here are the considerations you must observe to get the most out of Gramoxone or Liberty.

  1. Weather sensitivity.  The rate you need to use varies greatly with weather conditions and weed height.  If you’re spraying in the early spring with an overcast, 50 degree day you’ll likely need to wait until the weather warms up for best performance.  Here are a few key conditions that improve weed control:
    • Sunshine
    • Warmer temperatures (ideally 70 or 80 degrees)
    • Humid air
    • Active weed growth
  2. No root activity.  The alternative base products (Liberty and Gramoxone) are strictly contact herbicides that kill the aboveground portions of plants.  For annual weeds, this is not much of a concern.  For perennials, they simply won’t do the job Roundup will.
  3. Spray coverage is critical.  You need higher water volumes and higher spray pressure, likely from an extended range flat fan nozzle, to cover every leaf and growing point on the weeds to kill them.

Other Choices

  1. Sharpen.  This is a highly effective and fast-acting broadleaf burndown herbicide that has contact plus soil residual activity.  Sharpen can be used in front of a number of crops at varying rates.  The downsides are cost and lack of grass killing power.  Mix with Roundup to get the grasses.  Keep in mind, too, that the maximum rate in front of soybeans is just 1 oz. per acre, which leaves almost no residual.  Sharpen also can’t be used in combination with another PPO (e.g. Valor or Authority) in front of soybeans.
  2. Valor/Chateau.  This product provides good broadleaf burndown plus residual that can be used in front of a number of crops.
  3. Authority/Spartan.  Long-lasting residual herbicides like this normally don’t have the burndown activity that these products do.  Expect good burndown of small broadleaf weeds when used in combination with a base herbicide.
  4. Tricor (metribuzin).  This is a good choice to add especially in soybean burndown programs for burndown plus soil residual.
  5. 2,4-D and dicamba.  Both of these products are added to burndown programs often but should be used in the fall or very early spring to avoid crop injury and potential off-target issues.
  6. Aim.  Here’s a low-cost product with no residual that should be used more often in burndown in place of 2,4-D or dicamba.  It’s not as versatile as those others, but definitely has a fit.