Residue Removal Method and Herbicides for Tall Fescue Seed Production: II. Crop Tolerance
- George W. Mueller-Warrant ,
- William C. Young and
- Mark E. Mellbye
Increased reliance on herbicides for controlling weeds is a significant component of the ongoing transition from open-field burning (FB) to nonburn systems for grass seed production in the Pacific Northwest. Volunteer crop seedlings are the most abundant weeds present in many certified grass seed fields, but herbicide treatments to control them also have the potential to injure the established crop. Fourteen herbicide treatment sequences plus an untreated check were examined in five residue removal systems at two field sites during two consecutive growing seasons to determine their effect on tall fescue (Festuca arundinacea Schreb.) seed yield and harvest index. Herbicide treatments were applied preemergence (PRE) to seedling grasses in mid-October, postemergence (POST) in early December, or at both times. Tall fescue seed yield was not affected over a two-year period by competition from volunteer seedlings. Seed yield was reduced by herbicide injury, particularly in the second year. PRE applications of oxyfluorfen [2-chloro-l-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] reduced seed yield by 87 and 151 kg ha−1 in 1990 and 1991, respectively, compared with the average for three other PRE herbicides, pendimethalin [N-(l-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], metolachlor[2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide], and trifluralin [2,6-dinitro-N,N-dipropyl-4-(triHuoroniethyl)benzenamine]. The untreated check yielded 122 kg ha−1 more seed than the average of all 14 herbicide treatments in 1991. The least injurious herbicide treatment was PRE pendimethalin applied without subsequent POST herbicide. When applied following PRE herbicides, POST applications of 2.7 kg a.i. ha−1 diuron [N'-(3,4-dichlorophenyl)-N,N-dimethylurea] or 0.14 kg a.i. ha−1 oxyfluorfen plus 1.8 kg ha−1 diuron did not differ in yield or harvest index. An aggressive system for mechanical removal of straw, seed, and postharvest regrowth, vacuum sweeping (VS), reduced tall fescue seed yield and harvest index in 1991 compared with other, less aggressive, mechanical methods, and compared with two methods of burning. Some herbicide treatments applied to control volunteer crop seedlings had a greater effect on tall fescue seed yield than the adoption of nonburn methods of residue removal.
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