Warm‐season Grass Establishment with Atrazine1

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. Additional index words: Andropogon gerurdi Vitman, Bouteloua cumpendula (Michx.) Torr. , Erugrostis hichodes (Nutt.) Wood, Herbicide, Panicum virgutum L. , Selective weed control, Sorghusfrurn nutans (L.) Nasb. EED competition is a serious limiting factor in the W establishment of forage grasses from seed. Poor stands or complete stand failures may occur as a result of weed competition (4, 12). When weeds are controlled during the establishment phase of a new seeding excellent stands can be obtained (3, 12). Warm-season perennial forage grasses are particularly slow to become established from seed, often requiring 2 to 4 years from seeding before they can be grazed or harvested for hay (18). This slowness and uncertainty of stand establishment deters many farmers and ranchers from seeding warm-season grasses. One of the major reasons for the slow establishment is weed competition (2, 16, 17, 18). Cool-season weed species are especially competitive (16). Weed competition has reduced both forage and seed yield of grasses (2,6, 13). Uncontrolled weeds reduced 2nd year forage yields of big bluestem (Andropogon I Published as Paper No. 6583, Journal Series, Nebraska Agric. E3p. Stn. Received 19 June 1981. Professor, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583; Professor, Northeast Station, Univ. of Nebraska, Concord, NE 68728; and research agronomist, USDA, ARS and associate professor, Univ. of Nebraska, Lincoln, NE 68583, respectively. gerardi Vitman) and indiangrass [Sorghastrum nuta us (L.) Nash] 50 and 33%, respectively (2). Sideoats grama [Bouteloua curtipendula (Michx.) Torr. ] seed yields were increased 10-fold with adequate weed control (13). Atrazine [2-chloro-4-(ethylamino)-6-(isopropy1amino)-s-triazine) has been used successfully for weed control in established warm-season grasses (5). Atrazine and diuron [3-(3 ,4-dichlorophenyl)1, l-tiimethylurea] have been suggested for use on established warm-season grass seed production fields (5). Ethofumesate [( & )-2-ethoxy-2,3-dihydro-3 ,3-dimeth yl5-benzofuranyl methonesulfonatel has been used successfully to control annual bluegrass (Poa annua Id.) in Italian ryegrass (Lolium multgorum Lam.) seed fields (I 1). Post-emergence herbicides have been used effectively for weed control just prior to seeding and in new seedings of cool-season grasses (8, IO). The use of soil-applied herbicides for weed control in new grass seedings is a relatively new practice. Lee (9, 12) investigated the use of activated charcoal, banded over the seeded row to protect grass seedlings from atrazine, diuron, simazine [2-chloro4,6-bis(ethylamino)-s-triazine], and terbacil (3-tert-b~tyl-5-chloro-6-methyluracil). The activated carbon protected grass seedlings but usually resulted in poorer weed control in the carbon bands. McMurphy (14) evaluated propazine [2-chloro-4,6-bis(isopropylamino)s-triazine] , siduron [ 1 -(2-methylcyclohexyl)-3-phenylurea], and norea [3-(hexahydro-4,7-methanoindan-5y1)-1,l-dimethylurea] for use on new seedings of switchgrass (Panicum virgaturn L.) big bluestem, I ndiangrass, and sideoats grama. Sideoats grama was severely damaged by all the herbicides evaluated. Norea damaged all four of the grasses. Propazine did not damage switchgrass or big bluestem while sidurlon damaged only sideoats grama. Ertel et al. (Ertel, J . ! 3., E. J. Kinbacher, R. C. Shearman, and T. P. Riordan. 1979. Preemergence herbicide effect on estsrblishment of blue grama turf. Agron. Abstr. p. 121.) evaluated several herbicides on new seedings of blue grama [Bouteloua gracilis (H.B.K.) Lag X Steud. ] turf including atrazine, simazine, and benefin (N-butyl-N-ethyl-a ,a ,a-tnfluoro-2,6-dinitro-p-toluidine) with benefin being the safest. Kinbacher et al. (Kinbacher, E. J., J. S. Ertel, R. S. Shearman, and T. P. Riordan. 1979. Effect of preemergence herbicides on the establishment of buffalograss turf. Agron. Abstr. p. 122.) found simazine promising for use on newly seeded buffalograss [Buchloe dactyfoides (Nutt.) Engelm. ] turf. Research and commercial use on seed fields has demonstrated the safety of atrazine on establishced warm-season grasses. There has been evidence thiat s-triazine herbicides especially atrazine would be useful in establishing certain warm-season grasses from seed. With weed competition controlled, the time required for warm-season grasses to become established and productive would be reduced. This would make