No‐Till Warm‐Season Grass Establishment as Affected by Atrazine and Carbofuran

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AbstractTall growing, perennial, warm‐season grasses that produce 65 to 75% of their yield in mid‐summer may provide needed summer grazing; however, establishment is often slow and inconsistent when compared to cool‐season grasses. Improved establishment would make these warm‐season grasses less vulnerable to annual weed competition. No‐till plantings of switchgrass (Panicum virgatum L.) and Caucasian bluestem (Bothriochloa caucasica (Trin.) C. E. Hubbard] were made at Blacksburg, VA (37° 11' N° 80° 25' W, 610‐m elevation) on a Groseclose loam soil (clayey, mixed, mesic Typic Hapludult). Eight experiments included carbofuran (2,3‐Dihydro‐ 2,2‐dimethyl‐7‐benzofuranol methylcarbamate) at 0 and 1.1 kg a.i. ha−1 and atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) at 0, 1.1, and 2.2 kg a.i. ha−1 in all possible combinations. Seedling growth, leaf appearance rates, seedling weights, density, leaf elongation rates, and heights were measured. Yields of weedfree perennial warm‐season grasses were determined in the year of planting and the year after planting. Carbofuran at 1.1 kg a.i. ha−1 placed in the row with the seed at planting enabled seedlings to develop faster, elongate more rapidly, and provided more and heavier seedlings than without carbofuran. In the year after seeding, yields of warm season grass were higher where carbofuran was applied at seeding in seven of eight experiments. Atrazine reduced herbage yields as well as population, weight, development, and leaf elongation rate of seedlings in the seeding year. Atrazine at 1.1 kg a.i. ha−1 was not detrimental to either grass in the second year of the study. Atrazine at 2.2 kg a.i. ha−1 appeared to injure switchgrass more than Caucasian bluestem. Yields in the year after planting further confirmed these observations. Atrazine at 1.1 kg a.i. ha−1 increased yields over untreated controls. However, in one of four switchgrass experiments, yields of grass treated with atrazine at 2.2 kg ai. ha−1 were lower than controls the year after planting. A yield reduction was observed in two of four caucasian bluestem experiments. All stands were nearly pure with planted species the year after planting. Carbofuran and atrazine at 1.1 kg a.i. ha1 was considered the best recommendation for establishment of switchgrass and Caucasian bluestem under the conditions of the experiment.