TOLERANCE OF CREEPING RED FESCUE AND TIMOTHY TO HERBICIDES USED TO CONTROL CANADA THISTLE

Abstract

Field experiments at seven locations in northern Alberta confirmed that picloram (4-amino-3,5,6-tricholoropicolinic acid) is a useful herbicide for the control of Canada thistle (Cirsium arvense (L.) Scop.) in seed crops of creeping red fescue (Festuca rubra L.) and timothy (Phleum pratense L.). Dicamba (3,6-dicholoro-o-anisic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid) were less effective. Preplant herbicide treatments were tolerated by both grass species provided that one growing season elapsed between treatment and planting of the grasses. Fertile tiller production was increased in plants selected from field plots treated 1 yr earlier with picloram and transferred to a growth chamber for flowering and seed production. Seed production of timothy was not affected by 0.14 – 0.84 kg/ha of picloram applied at several growth stages. Fescue seed production was not affected by picloram treatments up to 0.56 kg/ha, but was reduced by most other herbicide treatments applied at 10% anthesis. In no instance did herbicide treatment result in more than a 10% reduction in germination of seed from either grass species and, except in the case of a dicamba treatment on timothy, seedlings appeared to be normal in all respects.