Establishment of Big Bluestem and Sand Bluestem Cultivars with Metolachlor and Atrazine

Abstract

AbstractWeeds interfere with big bluestem (Andropogon gerardii Vitman var. gerardii Vitman) and sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern.] establishment on rangeland and cropland in the central Great Plains of North America. A study was conducted to determine if metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylpbenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide] and atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] applied preemergence could improve establishment of big bluestem and sand bluestem cultivars. ‘Bonilla’, ‘Pawnee’, ‘Kaw’, and ‘Rountree’ big bluestem and ‘Goldstrike’ sand bluestem were planted in late May to early June 1989 and 1990 near Clay Center [Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll)] and Mead [Hastings silt loam (fine, montmorillonitic, mesic Udic Argiustoll)] in Nebraska. Metolachlor at 2.2 or 3.3 kg a.i. ha−1 and atrazine at 2 kg a.i. ha−1 were applied alone or in combination before weeds or seeded grass cultivars emerged. Stand frequency (the number of times the planted grasses occurred within sampling grids and expressed as a percentage of the total number of grids evaluated) and yield of the grass cultivars were measured the year after planting to determine establishment success. Grass stand frequencies were usually >50%, with or without herbicide treatment. Yield of big bluestem and sand bluestem cultivars was increased by at least 30% when herbicides were applied preemergence the year of planting compared with yield without herbicide. For each cultivar, yield and stand frequency were similar when metolachlor or atrazine at 2.2 kg a.i. ha−1 were applied. Therefore, metolachlor is a suitable replacement for atrazine to improve establishment of big bluestem and sand bluestem cultivars. However, yield and stand frequency of most grass cultivars were maximized when metolachlor and atrazine were applied in combination.