Some of the newest herbicides that have been registered here are those that are classified as PPO inhibitors. They fit well in this area because they generally have little soil residual activity that would cause problems to rotational crops and they work best under bright sunlight. Goal is one of the earliest registered of these (1980) but has only been used widely over the about the last 10 years. This is the only one of these that has problems with “lift off” or codistillation with water. The others include Aim or Shark, Chateau, Sharpen or Treevix, ET, and Sparten. They work as contact herbicides and do not move through the plant. Specifically, they inhibit protophorphyrin oxidase (PPO) which is an enzyme needed in the production of chloropyll. This causes a chain reaction that ultimately destroys cell memebranes. Within 12 hours the plant starts to show chlorosis. If the plant is small and the coverage is good, it will turn brown and die in 3 to 5 days. Activity is delayed if there is not bright sunlight. Sometimes activity is enhanced on the side of the bed that is exposed to the most sunlight. Contact herbicides are not usually thought of as having preemergence activity but when used at higher rates, Goal and Chateau do. As the hypocotyl emerges from the soil it contacts the herbicide and dies. For this reason it is important that the soil not be disturbed after application.

Click picture to listen to Barry's update

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.