Date of this Version
Agron. J. 74:916‑ 920
Weed competition is a limiting factor in warm-season grass establishment often delaying the first forage harvest 2 or 3 years. Weed control with herbicides could reduce this competition resulting in more rapid grass establishment. Field experiments were conducted to evaluate the effect of atrazine [2-chloro-4-(ethylamino)-6-(isopropy1amino)- s-triazine] on weed control, warm-season grass establishment, and forage yield during the seeding and following year. Several warm-season grass species were spring seeded at locations having distinctly different soils. The soils involved were a Butler silty clay loam (Abruptic Argiaquoll) containing 3.8% organic matter and a pH of 5.2, a Crofton silty clay loam (Typic Ustorthent) containing 2.1% organic matter with a pH of 7.2 and a Nora silty clay loam (Udic Haplustoll) containing 2.8% organic matter and pH 5.8. Atrazine at various rates was applied preemergence shortly after grass seeding and at one site it was atso applied the preceding fall. Weed control, grass establishment, and forage yield were measured the year of seeding and the following year. Uncontrolled weeds during the year of seeding reduced stands and 1st year forage yields of big bluestem (Andropogon gerurdi Vitman), indiangrass [Sorghusfrum nutuns (L.) Nash], sand lovegrass [Emgrostis trkhodes (Nutt. j Wood], sideoats grama [Bouteloua curtipendula (Michx.) Torr.], and switchgrass (Panicum virgatum L.). Big bluestem and switchgrass tolerated preemergence atrazine applications of 3.4 kgha on the Butler soil. Big bluestem was less tolerant of atrazine than switchgrass on the Crofton soil. Some atrazine tolerance was present in indiangrass but not in sand lovegrass and sideoats grama. Seeding year forage yields of big bluestem and switchgrass were significantly increased by atrazine. Weed control during the seeding year sometimes resulted in higher forage yields the following year. Big bluestem and switchgrass can he readily established and produce substantial forage yields the year of seeding by using atrazine for weed control. This would make these grasses more attractive to farmers and ranchers.