Tolerance of Five Cool‐Season Perennial Grasses to Selected Herbicides1

Abstract

AbstractSelective herbicides were applied in September or in April preceding production of the first or second seed crop of Kentucky bluegrass (Poa pratensis L.), smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), crested wheatgrass [Agropyron desertorum (Fisch. ex. Link Schult.)], and red fescue (Festuca rubra L.).Seed yield of these species was not reduced by isopropyl carbanilate (propham) or isopropyl m‐chlorcarbanilate (chlorpropham) at 3.4 and 4.5 kg/ha applied in September. Seed yield was significantly reduced by 5.6 kg/ha of propham applied in September to orchardgrass and chlorpropham applied in September to red fescue. Seed yield was not reduced by 3,6‐dichloro‐o‐anisic acid (dicamba) at rates as high as 4.5 kg/ha applied to Kentucky bluegrass in September, but was reduced by lower rates applied in April. Other species were less tolerant than Kentucky bluegrass to dicamba, applied in both September and April. Seed yield of Kentucky bluegrass was reduced by 4‐amino‐3,5,6‐trichloropicolinic acid (picloram) at 0.6 kg/ha applied in September before production of the first seed crop, but this species tolerated as much as 2.2 kg/ha applied to older stands. Other species were less tolerant than Kentucky bluegrass to picloram as they were to dicamba. Application of 2,4‐dichlorophenoxy)acetic acid (2,4‐D) up to 2.2 kg/ha in September did not significantly reduce seed yield of any of the species, but applications of 1.7 or 2.2 kg/ha in April reduced seed yield of smooth bromegrass and red fescue.Applications of propham, chlorpropham, or 2,4‐D did not reduce seed germination of any species. Application of picloram in September also did not reduce germination of grass seed, but application of 1.7 kg/ha or more in April reduced germination of smooth bromegrass seed in 1969 and red fescue seed in 1966 and 1969. Of all the herbicides, dicamba, particularly when applied in April, appeared to be the one most likely to reduce germination of seed of certain grass species.