There was a time when two of our better weed control chemicals were not actually classified as herbicides. Prior to the introduction of Basagran, the best control of cocklebur could be provided by a soil nematicide, DBCP, sold as Nemagon or Fumazone. The cocklebur activity was discovered by accident. DBCP was nasty stuff and the registration was cancelled not long after the cocklebur activity was discovered.
After we chased the cockleburs and morningglories around a while with Basagran, Blazer and the likes, we began to see a lot more sicklepod in Arkansas soybean fields. It was already a big problem in some of the Southeast states. While some herbicides had some activity on it, none were really good until Roundup Ready came along.
For a while though, an insecticide, toxaphene, would provide good control of sicklepod if applied in the cotyledon to one true leaf stage. We could not get sicklepod added to the label, but farmers were beginning to find a lot of worms in fields that had sicklepod! As with DBCP, the toxaphene registration was cancelled about the time it started to be used much for sicklepod control.
In a recent article I provided a progression of herbicides in soybeans up through the ALS-inhibiting herbicides such as Scepter, Classic and FirstRate as examples. Along the way there were different herbicides and mixtures in the existing modes of action that were introduced. However, the ALS inhibitors introduced in the early 1980s represent the last selective mode of action introduced in soybeans.
We had gone over 10 years without the introduction of a new mode of action before Roundup Ready was introduced and we have not had a selective mode of action introduced since. In fact, the last new selective mode of action, period, was the introduction of the HPPD or bleaching herbicides in corn around 1985. Examples of these are Callisto, Balance, and Laudis.
In addition, the nonselective modes of action like glyphosate and glufosinate (Ignite) are older as are some of the other herbicides like 2,4-D and dicamba that we may get to use with new trait technology. The fact that our newest herbicides are nearly 30 years old gives the weeds a lot of time to catch up.
In cotton the herbicide trends are similar to those in soybeans. We got the postemergence grass herbicides and then an ALS inhibitor, Staple, that provided some of the same weed control capabilities we had in soybeans. The ALS inhibitors were the last selective mode of action in cotton, and as in soybeans, we quickly had resistance issues with them. That is why most of the Palmer pigweeds in cotton and soybeans were resistant to these herbicides when the glyphosate resistance was documented.
I did not mention MSMA and DSMA in cotton when I was discussing johnsongrass in the previous articles and someone will likely ding me. Through the years these have been mixed with most everything used in cotton to provide annual grass and johnsongrass suppression. However they really did not provide effective control of rhizome johnsongrass.
Cotton and soybeans fit nicely together when discussing the progression of herbicide development. We use some of the same herbicides and most of the same modes of action in rice. I will focus on rice more in some later articles, but I want to finish my thoughts on cotton and soybeans in the next couple.
To this point I have brought things to the introduction of the Roundup Ready crops. I could see the Palmer pigweed issue beginning to swarm (as my grandmother would put it) about the time we got Roundup Ready soybeans into the research program. That technology changed the face of agriculture.