Almost all of the annual crops grown in the S.W. deserts of Arizona and California are grown in rotation with another annual crop. This reduces the flexibility growers have in using herbicides or other production practices that that change or persist in the soil. Sudan grass is commonly grown in rotation with lettuce or broccoli in this region. Tests have been conducted by University of California researchers that have indicated that sudan grass can have an adverse affect on both lettuce and broccoli when they follow sudan. When one crop has a negative impact upon another it is sometimes the result of allelopathy. Allelopathy is the inhibition of growth or germination caused by chemicals released by another plant. This is called autotoxicity when plants affect other plants of the same species. Alfalfa, for instance, is an example of autotoxicity. These researchers suggested that this problem could be avoided if lettuce or broccoli were not planted for 6 to 8 weeks after sudan was taken out or the residues were thoroughly leached.

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.