This is the time of year when burning fields becomes most widespread and some of the non-agricultural public are most likely to question this practice. Controlling weeds is often one of the reasons that are given for burning. There are probably several good reasons for burning wheat fields but controlling weeds is not one of them. Burning is a very old agricultural technique. It dates back to prehistoric times but is still used today. It is used here primarily as a post harvest technique to remove dead or dormant plant material. It is most common in the summer after grain harvest to facilitate ground preparation for the next crop or in the spring prior to regrowth of bermudagrass to remove stubble and stimulate regrowth. Burning for weed control doesn’t fit very well here following wheat harvest for a few reasons: 1) Wheat is probably one of the more weed free crops grown here. There are several effective grain herbicides and there is a low tolerance for green weeds in harvested wheat. There just are not that many weeds or weed seeds left to control after harvest. 2) Many studies have been conducted to evaluate burning as a weed control technique. It has been found that summer annual weeds are most affected by burning. Many of the winter annual weeds that we get in vegetables are unaffected as are those weeds that have hard seed coats. These include clovers, malva, dodder, sesbania and others. Burning also has little effect on many of the perennial weeds such as bermudagrass, field bindweed johnsongrass and nutsedge. 3) Some studies have found that burning is only effective on weed seeds that are on the soil surface. In one study they found that only 18% of the weed seeds that were buried 5mm (0.19”) or more were killed. 88% of those on the surface were controlled. 4) Some studies have indicated that hot and slow fires are more effective for controlling weed seeds than are the flash fires that are common here when wheat stubble is burned.

Click picture to listen to Barry

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.