Three Levels of Defense

We have nearly 500 million acres of cropland in the United States. Every acre is unique, from its soil type, to available nutrients and moisture to whether the landscape is gradient or flat. There is one characteristic common to every one of these acres: weeds.

Weed scientists have identified several key eras of weed management: 1941-1968, 1901-1940 and 1800-1900. In fact, the agronomic advancements made during those years is considered greater than the sum of all other periods since 6000 B.C.

Take, for example, the fact that we had 25 herbicides available in the U.S. and Canada in 1950. Just 19 years later, we had access to more than 100 herbicides.

Of course, technology has continued to evolve, but new chemistries and modes of action are not coming to market as frequently and quickly as they used to. The last time a new herbicidal mode of action was introduced was in the 1980s.

Hundreds, if not thousands, of new herbicides have come to market in the past few decades. But every one of those herbicides is based on a mode of action that existed previously. Even if a new mode of action were discovered today, it would take at least 10 years for it to become commercially available.

That doesn’t mean today’s herbicides are without innovation. It simply means we have to find the most effective way to use them and be judicious in their management.

Three Defenses

Herbicides have long been expected to provide growers with two defenses against weeds:

  • Burndown in the fall or spring and
  • Residual control of weeds until crop canopy for difficult, late-emerging weeds such as Palmer amaranth

A third and more recently introduced herbicidal feature is reactivation. People unfamiliar with the feature sometimes mistakenly assume it’s another way to say residual. In fact, reactivation is rather different.

When a herbicide provides residual control, it continues to control weeds as long as there is adequate moisture available. If there is a dry spell, the herbicide stops working. If it’s too early in the season, weeds continue to grow and you need to make another herbicide application.

With reactivation, the herbicide doesn’t stop working after a dry spell. Only IFT-containing products such as Corvus® and Balance® Flexx herbicide have this reactivation property. For Corvus and Balance Flexx to reactivate, it just takes a half inch of rain.

The figure below illustrates how reactivation works:

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