08/02/05 Labeled rates and weed resistance

Farm and Ranch August 2, 2005 Weed scientists now believe that following the recommended label rates is an important part of herbicide resistance management. That was one of the messages University of Idaho weed scientist Don Thill delivered at a recent field day. He explained what you may be doing if less than the minimum recommended rate is applied. Thill: "You may be selecting for weeds out there that have the ability to break the herbicide down. We call that metabolic resistance. The problem with that is if you get metabolic resistance it can be resistance to a number of different groups of herbicides so you would not have resistance to Group 1, maybe Group 2, Group 8, so on and so forth. So it would take out several herbicides if you got that type of resistance. So the recommendation is stay on label and don't use less than the recommended rate." Thill says the whole subject of herbicide resistance is getting complicated. He used the props of a baseball glove and balls to demonstrate target site resistance at the recent Parker Field Day. Thill explained how some herbicides with the same mode action, say those in Group 1, may still be effective against weeds thought to be resistant. That's because chemistries may be different. Some are referred to as "fops", others as "dims." Thill is working on a computer program that will help farmers with herbicide resistance management by showing what Group a branded product is in and if it is a fop or dim. The program will also be able to keep an historical record by field to help with crop rotation and plant back restrictions from herbicide applications. I'm Bob Hoff and that's the Northwest Farm and Ranch Report on the Northwest Ag Information Network.