Interactions Among Western Ragweed and Other Sandhills Species After Drought

Abstract

Interannual differences in yield and species composition of herbaceous vegetation on semiarid rangelands are common and often related to variations in precipitation regime. Interspecific interactions that occur after drought-induced population fluxes of western ragweed (Ambrosia psilostachya D.C.) were evaluated by removing western ragweed or associated species from 1-m 2 quadrats at weekly intervals beginning in early May, June, or July 1991 or 1992 on high-seral sandhills prairie in Nebraska. The composite of peak standing crops for ragweed and each group of associated species was 77% greater during May-October 1991 (2 252 kg•ha À1) compared with 1992 (1 275 kg•ha À1) when April and May precipitation was 98 mm below average and a late frost occurred. Mean levels of western ragweed herbage up to 436 kg•ha À1 had no effect on associated species in 1991 when above average precipitation occurred throughout the growing season. In contrast, when an unusually dry spring occurred in 1992, relatively small mean levels of ragweed (189 kg•ha À1) reduced end-of-season standing herbage of rhizomatous C 4 grasses on control plots by about 21% (137 kg•ha À1) with little effect on other associated species, regardless of when treatments were initiated. Within a given year, western ragweed density was seasonally constant, similar among treatments, and independent of preceding-year species composition. Severe defoliation of western ragweed had little effect on subsequent-year populations, indicating an ability to maintain primordia for several years with limited plant growth. Because western ragweed is not a strong competitor in the presence of vigorous graminoids, deferring use of June-or July-grazed pasture until after July in the subsequent year can minimize increases in western ragweed. Resumen Diferencias en el rendimiento interanual y la composició n de las especies de vegetació n herbá ceo en praderas semi-aridas son comú n y frequentemente relacionados con la variedad del regimen de precipiació n. Interrrelació n interespecífica que ocurre despues del cambio continuamente provocado por la seguía en la ambrosía del oeste (Ambrosia psilostachya D.C.) fueron evaluadas con quitar la ambrosía del oeste y especies asociadas de 1-m ˙ en intervalos cada semana empezando en mayo, junio, o julio de 1991 o 1992 en praderas de alto crecimiento en Nebraska. El compuesto de cosechas de ambrosía en su punto má ximo y cada grupo de especies asociadas fue 77% mayor durante mayo-octubre de 1991 (2,252 kg ha À1) comparado con 1992 (1,275 kg ha À1) cuando la precipitació n en abril y mayo fue 98 mm menos del promedio y occurio una helada tardia. El promedio de ambrosía del oeste hasta 436 kg ha À1 no tuvo ningun efecto en especies asociadas en 1991 cuando ocurrio precipitació n má s alla del promedio durante el periodo de crecimiento. En contraposició n, cuando ocurrio una sequía durante la primavera en 1992, relativamente pequeñ os niveles de ambrosía (189 kg ha À1) redujeron la cosecha al fin de la temporada de zacate rizomato C4 en terre...

Western Ragweed (Ambrosia psilostachya) Control and Bermudagrass Response to Diflufenzopyr Tank-Mix Combinations

“…Vermeire and Gillen (2000) reported standing crops of western ragweed at 600 kg ha À1 can be tolerated before control should be considered. However, Reece et al (2004) reported that seasonal grass production on the sandhills prairie was reduced 21% when western ragweed herbage levels of 189 kg ha À1 were present following dry weather in the spring.…”