Yuma County, Arizona
May 7, 2001
Yuma County Office
solani is usually of minor importance in Arizona, but the fungus can
cause severe stand loss in some situations. Rhizoctonia is very versatile
and can cause decay of the roots, 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.
Alfalfa caterpillar, Colias eurytheme, also known as alfalfa
butterfly, is a warm weather pest of alfalfa. There can be as many as
seven generations between May and October, in the low desert. Start checking
fields for alfalfa caterpillars when yellow alfalfa butterflies first
appear in May. When alfalfa butterflies are seen flying over tall alfalfa,
they most likely emerged from that field. Eggs are laid singly, standing
on end, on the upper surface of leaves in fields with re-growth under
6 inches. Larvae hatch in 3 to 10 days, grow to about an inch long and
pupate in approximately two weeks. Alfalfa caterpillars are green with
white stripes down their sides and are distinguished from beet armyworm
by their velvety appearance. Monitor fields weekly from June through October,
checking 2 to 3 times per week during periods of heavy infestations. Take
5 sweep counts in 4 to 5 field locations. Check worms for parasitism by
pulling heads off an alfalfa caterpillar larva, squeeze out the body contents,
and looking for an Apanteles wasp larva. Treat when field counts
average 10 non-parasitized caterpillars per sweep.
Weed Control: Some herbicides, such as Sencor, can be impregnated onto fertilizer to increase crop safety and soil deposition. This can be effective with soil applied herbicides that are taken up through the roots or shoots of target weeds.
10 Year Summary (April 23, to May 6, 1992-2001):
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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Information provided by:
Barry Tickes, firstname.lastname@example.org Extension Agent, Yuma County
Michael Ottman, email@example.com Agronomy Specialist
College of Agriculture, The University of Arizona.
Eric Natwick, firstname.lastname@example.org UCCE Imperial County - Farm Advisor
University of California, Davis, CA.
Material written May 7, 2001.
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