Production Update:

Rhizoctonia: Rhizoctonia solani is usually of minor importance in Arizona, but the fungus can cause severe stand loss in some situations ( picture). Rhizoctonia is very versatile and can cause decay of the roots ( picture), stem, and leaves as well as the crowns. Symptoms usually occur during the warmer part of the growing season. Circular, concave, black lesions can appear on taproots but are not always seen in Arizona. Crown decay appears as dark, rotted areas within the crown tissue. The fungus can also girdle the stem near the soil line. The disease can cause circular lesions on the leaves. Control measures include resistant varieties, proper land leveling, and avoiding over-irrigation. No effective chemical control measures exist for rhizoctonia.

Insect Management: The granulate cutworm, Agrotis subterranea, (Fabricius) (picture), is a devastating pest of bed planted alfalfa and is also an occasional pest of flood irrigated alfalfa. The cutworm larvae often go undetected until after cutting or hay removal. When fields are watered back, there may be areas of little or no regrowth due to cutworms feeding on new shoots from alfalfa crowns. Granulate cutworm is nocturnal and will move from cracks in the soil or from under duff in the evening and climb into the alfalfa canopy to feed. Some of the cutworms feed on new shoots under the duff, holding back regrowth, depleting starch reserves in the crowns and thereby weaken the plants. Weakened plants are more susceptible to disease. Permethrin, cyfluthrin and endosulfan are insecticides that control this pest. Cutworms feeding under the duff may escape insecticide treatments.

Weed Control: Dodder ( picture) has become increasingly widespread in some areas of Yuma County. Multiple applications of Trifluralin will control this parasite prior to emergence. It cannot be selectively controlled once it has emerged and become attached to alfalfa.

10 Year Summary (April 20, to May 3, 1995-2004):

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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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