One chemical dealer joked to another at a recent field day in central Indiana that the Indiana tree isn't really the Tulip tree. The official state tree should be giant ragweed, because they grow that tall in his area. And even common ragweeds qualify in some places, he added.
If you're trying to take down trees, there may not be much chemistry that is going to help at this point. As long as they're not resistant to the chemistry, you may get some effect. Total control would involve lots of luck and prayer. Purdue University weed control specialist Bill Johnson has used 'luck and prayer' as a recommendation when asked how to take down tall weeds in V8 or larger corn before.
The secret, of course, is to get the weeds before they get to that point. Weather didn't cooperate in all cases this year, letting weeds get ahead in some situations. One problem continues to be, however, that people overestimate what size of weed a herbicide can control.
For example, if you apply Atrazine post in corn because you're tying to get help on picking up grasses, that's fine, as long as the grasses are small. And according to label directions, that's 2 inches or less. Atrazine isn't going to be much help on 4 or 6-inch foxtail, let alone stuff that is ranker than that.
"You've got to know what the herbicide can do and what its limitations are,' says Bob Hooten of FMC. Once primarily a company that marketed insecticides, FMC became a credible herbicide supplier with Authority and Cadet. They hope to become even more of a player in the market once their most recent entry, Anthem, receives a label, hopefully next spring. It will likely be introduced in 2013 in a full launch of the product.
It doesn't matter what the product is, Hooten notes, there are limits as to what size weed it can control. He advises that farmers check labels carefully before spraying a product. Otherwise, they may wonder why it didn't work, or worse yet, blame it on a dealer or the weather when the real problem was simply trying to use the product in a way it wasn't developed or intended to be used.