Pigweed is a summer annual weed that can persist into the winter and cause problems in early season lettuce. There are 4 species of pigweed here that are all common and widespread. Palmer Ameranth is probably the most common. It is very aggressive and can grow to 6 ft. in height or higher. It has distinctive white veins on the underside of the leaves. This is the one that has become resistant to glyphosate in many agricultural areas including central Arizona. Redroot pigweed is probably the second most common . It is shorter and has stiff spiny scales. The lower stems are often red in reddish Tumble pigweed is much different. It is shorter, grows low to the ground and has smaller leaves. The branches are sticky and break off when mature and tumble in the wind. Prostrate pigweed is similar to tumble pigweed but the leaves are even smaller and create mats on the ground. All of these species need to be controlled before they become well established. Of the three preemergence herbicides registered on lettuce, Prefar is the most effective and Kerb is the least effective on pigweed. Balan is between these two. Cultivation and hand weeding are the only options if these fail. Kerb is the broadest spectrum herbicide on lettuce but this is one broad leave weed that can be more effectively controlled with Prefar and Balan.

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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.