It can be a challenge to selectively control weeds in vegetables with the limited number of herbicides that are registered on specialty crops. You have the next 5 or 6 months to control the bank of weed seeds that can be a problem after you plant fall vegetables. This involves keeping weeds in the current crop from producing seed and extends through the summer crop or fallow period.

Much of the wheat and cotton that are in the field now will be followed by vegetables. There are more herbicides registered for use in cotton than for any other crop grown in Arizona and with proper management, weeds should not be a problem. The herbicides that are available for use in wheat and barley is more limited although there are tools for controlling almost all of the common weeds in these crops. Nonetheless, we get calls about this time every year on what can be done now to control weeds that should have been treated earlier. At this point, it is usually necessary to wait until the wheat is maturing before applying preharvest treatments to desiccate weeds that are green, contain too much moisture and reduce grain quality. There are herbicides that are registered for preharvest use after the grain is in the hard dough stage and contains less than 30% moisture. These include both systemic herbicides like glyphosate and some PGR’s and contact herbicides like Aim. ET, Gramoxone, bromoxynil and others. Not all of these are registered here and labels need to be checked.

Fallow periods before vegetables are planted offer an excellent opportunity to control weeds that cannot be selectively controlled after the crop is planted. Depending on the length of time the field will be fallow, almost every weed can be controlled. Even very difficult perennial weeds like nutsedge can be controlled at this time. The Eptam/ fallow technique is an example of an effective and affordable treatment if 40 to 60 days are available. Non chemical treatments like flooding and solarization have proven effective in controlling not only weeds but diseases as well. At the very least, weeds can be germinated and disked to reduce the seed bank prior to planting.

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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.