Although it happened many years ago, I remember my first experience with spray tank contamination as if it happened this past season. The year was 1991 and nearly constant rains had us moving from site to site in search of “dry” ground to drive on. Rigs buried in mud and partial loads left in tanks overnight were the norm. The rig was a Spray Coupe with a massive 40 foot boom. The culprit was a plant growth regulator based herbicide presumed to have been completely cleaned out prior to switching to soybeans. The proof that it was not completely cleaned out showed up 4-5 days later when the headlands and first pass were obviously injured – injured enough to be noticed in a windshield survey at 50 mph! Fast forward to 2016. The equipment is larger. Pesticide labels now provide very specific cleanout procedures. And yet as I drive this state traveling between research trials, it seems that herbicide injury is just as prevalent as ever. Although spray drift can be blamed for some of the incidents, tank contamination with its classic appearance of straight lines and inverted-V shaped symptoms appears to be responsible for many of the cases. Applicator understanding of pesticide chemistry, formulation and herbicide injury symptoms is critical for proper sprayer cleanout and avoidance of these costly mistakes.
Soil Science Extension
University of Wisconsin Madison