Tolerance of Southern Pine Seedlings to Clopyralid

Tolerance of three pine species to postemergence applications of clopyralid was examined at ten southern nurseries over a 2 yr period. The herbicide was applied at various times during May, June, and July. At time of lifting, seedling morphology was evaluated (root-collar diameter, shoot height, root dry weight, and shoot dry weight). Loblolly pine (Pinus taeda L.), slash pine (P. elliottii Engelm. var. elliottii) and longleaf pine (P. palustdds Mill.) were tolerant to 210 to 840 g acid equivalent (ae)/ha. However, epinasty was occasionally observed on both loblolly pine and slash pine. The injury symptoms were ephemeral and seedlings appeared normal 3 months after treatment. Results from these tests suggest some pine species are tolerant to this herbicide at the seedling stage. As a result of this research, this herbicide can be legally used in many southern pine nurseries to control troublesome weeds such as sicklepod (Cassia obtusifolia L.), Florida beggerweed (Desmodium tortuosum [Sw.] DC.), horseweed (Erigeron canadensis L.) and other annual broadleaf weeds. South. J. Appl. For. 24(1):51-56.