Don’t be surprised if herbicides that are effective in other more mild climatic regions don’t work here, especially during the hot months. Low desert weeds have developed physical characteristics and growth habits that allow them to survive in hot and dry conditions. It is not uncommon for the weed species to have a different response to herbicides in the California central valley than they do in the low desert. Desert weeds typically have a thicker cuticle or skin to help conserve water. Liquid fertilizer and some of the contact herbicides are often more effective in the central valley than they are here. Liquid fertilizer can be used to control weeds in some milder regions but just make desert weeds grow better. Even some of the most effective systemic herbicides are less effective here than they are in the central valley. During the hot time of the day and when desert weeds are stressed for moisture, even a gallon of Glyphosate can be ineffective. The stomata or pores on the leaves close down, transpiration is reduced and herbicides are not translocated very effectively through the plant to the site of action. The plant is in survivial mode. Some species like purslane or pigweed, store water in their leaves and stems and can survive some pretty hot and dry conditions and start to actively grow again when it cools down or moisture becomes present. Some species have below ground vegetative structures that help them survive. Nutsedge, bermudagrass and perennial johnsongrass are examples of these. In general, the better the weeds are growing the better the herbicides will work and it is best to apply herbicides during the morning or evening when stress is reduced.

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.