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Southern Rust active in KansasDavid G. Hallauer District Extension Agent, Crops & Soils/Horticulture I've mentioned corn foliar diseases here before--here's yet another: Southern Rust. KSU Plant Pathologist Dr. Doug Jardine noted southern rust earlier in the week of July 21, in Manhattan, a little earlier find than normal. Combined with late developing corn, it could cause some problems on susceptible hybrids. Symptoms of southern rust resemble those of common rust with subtle differences Lesions are light cinnamon brown to orange in color and usually circular to slightly oval in shape, ranging in diameter from 0.2 to 2.0 mm. They tend to be densely scattered on upper leaf surfaces and uncommonly found on the under side of the leaf. Lesions of common rust will be larger, less dense on the leaf, be more elongated in shape and can readily be found on both the upper and lower surfaces of the leaf. It is possible to have both rusts on the same leaf. Susceptible varieties that have not reached the soft dough stage of development may benefit from a fungicide application given the yield potential of the current crop and the high prices. Be sure to be aware of pre-harvest interval restrictions for triazole fungicides (Quilt--30 days, Stratego--no application after brown silk, Tilt--30 days, Bumper--30 days and Propimax--30 days). Pre-harvest intervals apply to both forage and seed harvest. Fields sprayed previously for gray leaf spot should be protected from southern rust. Warm, humid temperatures with nighttime dews will favor continued infection. Defoliating caterpillars If you've ever walked outside to find a tree suddenly defoliated, you're not alone. We usually assume it happened overnight, when in actuality, the caterpillars had been present for 5 to 6 weeks. During this period, noticeable damage was not evident due to the small size of the caterpillars. However, during the final days of their feeding cycle, the large larvae voraciously "gobble-up" any and all foliage. While there are several butterfly species whose larvae are defoliators, the majority of defoliating caterpillars are associated with moths. Currently, two "cousin" species are present: Walnut caterpillar moths and yellow-necked caterpillar moths. Although there are overlaps in tree species that are "attacked," walnut caterpillars have a restricted preferred host range (walnut, pecan, hickory), whereas yellow-necked caterpillars are associated with a greater variety of fruit and shade trees (apple, peach, cherry, crabapple, elm, maple, oak, birch and locust). The yellow- necked caterpillar produces but a single generation/year whereas walnut caterpillars produce two. One cannot predict where these caterpillars will eventually show up in damaging numbers! Its possible that many trees serve as host to low numbers of these caterpillars. But because of those low numbers and the absence of noticeable damage, they complete their cycle unseen. Only in "outbreak" situations do they come to our attention. And at that point, there is nothing to be gained by applying insecticide treatments because most caterpillars have neared the end of or have completed their feeding cycle and may have left to seek protected sites in preparation for overwintering. The best news is that although current-season foliage has been destroyed, next year's buds are not damaged, and trees will fully leaf out the following spring. 8/4/08 Date: 7/31/08 Advertisement
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