Evaluation of Pendemethlin for Selected Containerized Perennials

Abstract

Specialty crops generate $40 billion in annual sales comprising a significant portion (40%) of total agricultural sales. The diversity of plant material is a limiting factor for new herbicide registration. The IR-4 program facilitates the labeling of new or experimental pesticides for minor use crops. The objective of this experiment was to determine the ornamental phytotoxicity and efficacy of Pendemethalin for selected 1-gallon perennials. Phytotoxicity was evaluated on Armeria maritime, Boltonia, Buddleaia davidii, Cercis Canadensis, Delphinium, Fragaria, Oenothera, Panicum virgatum, Papaver orientale, Phlox subulata, Rudebeckia fulgida, Scabiosa columbara, Schizachyrium scoparium and Sedum spectabile. Herbicide was applied at 1X, 2X, and 4X rates according to IR-4 protocols with a weedy check included. Pendemethalin was applied twice throughout the study, the second spray occurring two months after the first. Visual ratings were taken of efficacy (scale, 0-10) and phytotoxicity (scale, 1-10, 10 = complete kill) at 15 and 45 days after treatment (DAT). Buddleaia displayed symptoms of phytotoxicity at the 4x rate but grew out of the initial effects of the herbicide. By trials end, Oenothera at 1×, 2×, 4× rates, Fragaria and Phlox at 2× and 4× and Canadensis at 4× had significantly reduced plant quality. All remaining species had acceptable plant quality. Efficacy was evaluated following the same protocol as above with a weedy seed check using a 1/8th tsp.mixture of Digitaria sanguinalis, Poa annua, and Senecio vulgaris per 1-gallon pot. Overall no treatment provided an acceptable level of weed control. The herbicide provided little control of Groundsel, was moderately effective in controlling the Bluegrass, and provided 100% control of the Crabgrass.