Flooding to Kill Weed Seeds During Summer Fallow (July 8, 2015)

Prolonged flooding during the hot summer months is one of several non-chemical techniques in use locally to control weed seeds. The primary objective of this technique is to control diseases although weed control can be an added benefit. The effect of prolonged flooding on diseases is well documented but its effect on weed seeds is inconsistent and variable depending upon several factors including weed species, depth in the soil, duration and depth of water, temperature and other factors. This technique works better here in the low desert than it does in many places because of the high temperatures and high respiration demands. The availability of oxygen is cut off to the roots when it is most needed. It is still necessary to keep the field continuously flooded at a depth of 6 to 8 inches for 3 to 8 weeks. Some species are much more sensitive than others to this technique. Perennial weeds are more sensitive than are many annual weeds. Pigweed, field bindweed and nutsedge survive while many annual grasses do not. The ability of some species to develop adaptive traits that allow them to survive has been reported. For instance, some have developed the ability to elongate above the water line or store carbohydrates go dormant during flooding.

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To contact Barry Tickes go to: btickes@ag.arizona.edu.