Yield and Nutritional Quality of Intermediate Wheatgrass Infested by Black Grass Bugs at Low Population Densities

Abstract

Highlight: Black grass bugs (Labops hesperius) at a population density of 156 bugs per square meter did not affect herbage yields of intermediate wheatgrass but depressed seedhead production 56%. They caused a small but significant increase in concentrations of crude protein and a slight decrease in cellular contents.An important question in the management of wheatgrass monocultures during recent years has been the effect of the grass bug Labops spp. (Hemiptera: Miridae) on forage yields, forage quality, and stand longevity. Grass bugs occur throughout the Intermountain and adjacent areas (Bohning and Currier 1967; Denning 1948;Todd and Kamm 1974) and have been reported to cause extensive damage to crested wheatgrass (Agropyron cristatum) and intermediate wheatgrass (A. inter-medium) stands in some areas (Knowlton 1967;Haws et al. 1973). Their effect on nutritional quality of forage has remained virtually unknown, although Todd and Kamm ( 1974) inferred significant short-term losses in a recent Oregon study.The study reported here was initiated to determine the effects of relatively low population densities of black grass bugs (Labops hesperius) on yield and nutritional quality of intermediate wheatgrass. Methods and MaterialsTwo intermediate wheatgrass seedings were selected as study areas in the spring of 1974. Major criteria used in selection of these areas included uniformity of soils, topography, and grass stands and presence of grass bug populations that were large enough to impart the characteristic yellowing of the grass leaves, commonly attributed to feeding activities.

Crested Wheatgrass Vigor as Affected by Black Grass Bug and Cattle Grazing

“…No insect population data were taken in 1976. However, Browsers (1976) found 200 black grass bugs per rnr in early June 1975 and Malechek et al (1977) found between 30 and 156 insects per rnz in early June 1974.…”

“…Grazing data are shown in Table 1. Herbage production at Sterling Ranch is about 1700 kg/ ha (1500 lb/acre) annually (Malechek et al 1977). Proper use (33% total production) is therefore 560 kg/ ha or, about 1.54 AUM perhectare (assuming one AUM requires 363 kg air dry forage).…”

“…Moderate to heavy populations of black grass bugs (100 -I-per m*) have also reduced total dry weight production, digestibility, nutritional value, and palatability (Bohning and Currier 1967, Todd and Kamm 1974, Higgins et al 1977. Lower populations (less than 100 per mz) did not significantly affect dry herbage yield or digestibility (Malechek et al 1977).…”

Journal of Range Management, Volume 54, Number 4 (July 2001)

“…The large areas of a single species of grass provided an excellent niche for the black grass bugs (Higgins et al 1977). A density of 156/m 2 reduced seed head production in intermediate wheatgrass by 56% (Malechek et al 1977). Ansley and McKell (1982) showed the black grass bug feeding reduced leaf length, seedhead height and carbohydrate reserves in root crowns in crested wheatgrass.…”