Evaluation of Aminopyralid Applied PRE to Control Western Ragweed (Ambrosia psilostachya) in Oklahoma Pastureland

Abstract

Western ragweed is problematic in Oklahoma pasture and rangeland. There are no labeled PRE herbicides for western ragweed control in pastures to allow ranchers the flexibility of extending the spray season or the ability to spray before emergence of sensitive crops in bordering fields. Field studies were conducted in four locations during a 2-yr period to determine the effects of applying aminopyralid PRE for control of western ragweed. Good to excellent control of western ragweed was obtained when aminopyralid rates of 89 g ae ha−1 or greater were applied PRE. Control was season long and equal to that obtained with a formulated mixture of 2,4-D and aminopyralid applied POST at a rate of 457 + 57 g ae ha−1. Sward height at time of PRE application had little to no effect on the efficacy of the treatment, but time after application before a significant rainfall event did influence the aminopyralid rate needed to achieve acceptable PRE control.

The Worldwide Spread, Success, and Impact of Ragweed (Ambrosiaspp.)

“…In its native range in North America, A. psilostachya shares ruderal habits with A. artemisiifolia, as it is common in open disturbed habitats such as abandoned fields, vacant lots and along transportation corridors (Basset and Crompton, 1975). In contrast to A. artemisiifolia, however, it is also common in semi-natural/natural environments: it is a typical forb of tallgrass prairies (temperate grasslands) of the American Great Plains (Reece et al, 2004) and a weed in pastures and rangelands where it is favoured by overgrazing and fire (Baker and Guthery, 1990;Abrams, 1988;Vermeire and Gillen, 2000;Funderburg et al, 2014). It is a sand-loving species and colonizes dry sand prairies on sand hills (Hart and Gleason, 1907;Hulett et al, 1988;Ebinger et al, 2006;Uresk, 2012).…”