AbstractExotic annual grasses such as medusahead [Taeniatherum caput-medusae(L.) Nevski] and downy brome (Bromus tectorumL.) dominate millions of hectares of grasslands in the western United States. Applying picloram, aminopyralid, and other growth regulator herbicides at late growth stages reduces seed production of most exotic annual grasses. In this study, we applied aminopyralid toT. caput-medusaeto determine how reducing seed production in the current growing season influenced cover in the subsequent growing season. At eight annual grassland sites, we applied aminopyralid at 55, 123, and 245 g ae ha−1in spring just beforeT. caput-medusaeheading. The two higher rates were also applied pre-emergence (PRE) in fall to allow comparisons with this previously tested timing. When applied in spring during the roughly 10-d period between the flag leaf and inflorescence first becoming visible, just 55 g ae ha−1of aminopyralid greatly limited seed production and subsequently reducedT. caput-medusaecover to nearly zero. Fall aminopyralid applications were less effective againstT. caput-medusae, even at a rate of 245 g ae ha−1. The growing season of application, fall treatments, but not spring treatments, sometimes reduced cover of desirable winter annual forage grasses. The growing season after application, both spring and fall treatments tended to increase forage grasses, though spring treatments generally caused larger increases. Compared with other herbicide treatment options, preheading aminopyralid treatments are a relatively inexpensive, effective approach for controllingT. caput-medusaeand increasing forage production.
Studies on the Seed Production of Some Forage Grasses : I. On the suitable seed harvesting times of some grasses : II. On the tillering of orchard grass
