Control of Nuttall's thistle in perennial grass pastures

Abstract

AbstractNuttall's thistle (Cirsium nuttalli DC) is a biennial species that deters grazing during dry seasons in Florida when forage is limited. Although management of other thistle species has been extensively studied, information on Nuttall's thistle control is limited. Field studies were conducted to compare the effectiveness of aminopyralid, dicamba, and 2,4‐D for Nuttall's thistle control applied at two different timings (rosette vs. bolting). A second experiment was conducted to determine the most effective aminopyralid rate through field dose–response studies. Although control of bolting plants was initially greater than control of rosette thistle at 15 d after treatment (DAT), no differences were detected between growth stages at 30 and 60 DAT. Excellent control (>90%) was achieved at 60 DAT with both rates of dicamba + 2,4‐D [4.0 + 11.4 and 6.0 + 17.2 oz acid equivalent (ae) acre−1] and aminopyralid at 0.77 oz acre−1, whereas aminopyralid at 0.26 oz ae acre−1 and both rates of 2,4‐D (7.0 and 14.0 oz ae acre−1) provided 82, 80, and 78% control, respectively. The dose–response field experiment indicated that the aminopyralid effective dose required for 90% control (ED90) was 0.34 and 0.94 oz ae acre−1 for rosette and bolting thistle at 30 DAT, respectively. No difference between timings was detected at 60 DAT and the aminopyralid ED90 value was 0.27 oz acre−1. These data indicate that dicamba + 2,4‐D (6.0 + 17.2 oz ae acre−1) effectively controlled Nuttall's thistle; similar performance can be obtained with low aminopyralid rates (0.27 oz ae acre−1).