Chinch Bug Resistance in Commercial Grain and Forage Sorghum Hybrids

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CHINCH BUG RESISTANCE IN COMMERCIAL GRAIN AND FORAGE SORGHUM HYBRIDS
Gerald Wilde, Terry Mize, Jeff Stuart.
Chinch bugs constitute a limiting factor to sorghum production in some areas. In recent years, growers in central and eastern Kansas, southeastern Nebraska, western Missouri, and parts of Oklahoma have lost millions of dollars from chinch bug damage. The majority of these losses have been due to severe early season stand reductions resulting from nymphal migration from maturing wheat fields to adjacent or nearby fields of young sorghum. In addition, mid-summer infestations from second generation chinch bug populations have caused damage and yield reduction.
From many interested growers we receive questions, some prompted by seed company advertisements, about chinch bug resistance in commercial grain and foragesorghum hybrids. During the last 4 years wehave tested a few commercial grain and forage-sorghum hybrids to determine if there are significant differences in chinch bug resistance among hybrids currently available. We designed these tests in two ways: (1) to compare yield and damage of hybrids in sprayed with those in nonsprayed field plots; and (2) to compare yield and/or damage in unsprayed field plots. In addition, chinch bug damage ratings were made on the Republic County Grain Sorghum Two studies conducted in 1979 with a small number of grain sorghum hybrids suggested that they do differ in their respon se to chinch bugs. Yield loss in one test ranged from 6 to 43% (Table 1) and. the d amage rating ranged from 2.0 to 4.7 in the second (Table 2). Similar d ifferences were noted in two 1981 grain sorghum tests in whi ch the yield loss ranged from 8 to 79% in one test (Table 3) and the percentage of plant survival ranged from 16.4 to 80.7 in another (Table 4).
Our studies indicate that there are differences in chinc h bug damage among different hybrids but that considerable variation is present; they also reveal some environmental effects on t he expression of resistance. A hybrid may be low in damage in one test (but not significantly lower than damage on several other hybrids) and moderately high in damage in another test. We have found that hybrids with Kafir paren ts tend t o have more resistance to chinch bugs than other hybrids do. Also, some hybrids are quite susceptible to c hinch bugs and the risk of severe loss in yield is greater in the fields where those hybrids are planted if seve re c hinch bug pressure develops. The res istance that is present in hybrids c urrently grown extensively is useful primarily against mid-season infest ations and is not high enough to prevent damage in small seedlings subject to heavy infestations. Therefore, a planting time or rescue insecticide treatment should be used to provide maximum protection to plants during their early stages of growth. Our tests do show that when treated with insecticides, lines with some chinch bug resistance withstand attack better than do more susceptible lines (Table 5).
We suggest that a grower use this information in combination with two or three y'ears sorghum p erformance data (available from the Experiment Station or County Extension Office) that are most nearly appli cable to one's own farm. This information should be carefully • Difference between no chinch bugs and chinch bugs present on the same hybrid significantly different at 5% level.
studied to determine the following: (1) which hybrids show t he least damage but yield best under the impact of chinch bug infestations; and (2) if c hinch bugs failed to develop, which hybrids yield best under chinch bug-free conditions. W e are currently involved in a search for new an better sources qf resistance and have identified some lines that may be useful in further reducing losses caused by chinch bugs.   This publication from Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information: http://www.ksre.ksu.edu.