| Abstract/Contents: | "AC 263,222 (imazapic), formerly known as imazameth, has shown promise for leafy spurge control in North Dakota. However, grass injury especially to cool season species has been observed. The labeled rate for optimal leafy spurge control is AC 263,222 at 2 oz/A, applied with a methylated seed oil and nitrogen fertilizer 2 weeks before a killing frost. The objectives of this research were to evaluate AC 263,222 applied with and without adjuvants and applied in the mid-summer or fall to maximize leafy spurge control with minimal grass injury. The first experiment evaluated AC 263,222 applied in the mid-summer or fall for leafy spurge control at locations near Valley City and Jamestown, ND. Mid-summer treatments were applied to the flowering stage of leafy spurge in early July and fall treatments during regrowth in September. The treatments included AC 263,222 at 2 or 4 oz/A alone, or at 1 or 2 oz/A plus methylated seed oil (MSO) at 1 qt/A applied in mid-summer or fall. The standard treatments for comparison were picloram plus 2,4-D at 4 plus 16 oz/A applied in mid-summer, or at 8 plus 16 oz/A applied in the fall. Mid-summer treatments were reapplied when leafy spurge control was 70% or less 12 months after treatment (MAT). All treatments at Jamestown were reapplied, but only two treatments (AC 263,222 at 1 oz/A plus MSO and AC 263,222 at 2 oz/A) were reapplied at Valley City. Leafy spurge control with AC 263,222 applied in mid-summer increased from 3 to 10 MAT. AC 263,222 did not visibly control leafy spurge top growth 3 MAT, regardless of rate or adjuvant. However, AC 263,222 at 4 oz/A alone or 2 oz/A plus a MSO averaged 90% control 10 MAT. Grass injury 10 MAT at Valley City averaged 28% but was not visible at Jamestown. AC 263,222 at 4 oz/A provided 82% control 15 MAT, but 4 oz/A is twice the labeled rate. AC 263,222 provided better leafy spurge control when applied in the fall than mid-summer. All fall-applied AC 263,222 treatments 9 MAT averaged 100% control and 22% grass injury. AC 263,222 at 4 oz/A alone or 2 oz/A plus a MSO maintained 96% control 12 MAT with no grass injury. The second experiment evaluated AC 263,222 applied with or without adjuvants near Walcott, ND. The treatments were AC 263,222 at 1 or 2 oz/A alone, or with 1 qt MSO, 1 qt 28% N, or 1 qt MSO plus 1 qt 28% N. Pictoram plus 2,4-D at 8 plus 16 oz/A was applied as a standard treatment. Treatments were applied September 4, 1996, to leafy spurge at the fall regrowth stage. Herbage and leafy spurge were harvested 10 MAT, and dry weights were obtained to evaluate the effect of AC 263,222 on herbage and leafy spurge yield. AC 263,222 provided better leafy spurge control at 2 oz/A than at 1 oz/A, but a MSO was necessary to provide long term control. AC 263,222 at 2 oz/A, regardless of adjuvant, and AC 263,222 at 1 oz/A plus MSO averaged 98% leafy spurge control 9 MAT. Leafy spurge control 12 MAT was the best with AC 263,222 at 2 oz/A plus MSO and AC 263,222 at 2 oz/A plus MSO plus 28% N, which averaged 66% with only 6% grass injury. AC 263,222 plus MSO decreased leafy spurge dry weight more than the herbicide alone at comparable rates. For example, leafy spurge yield with AC 263,222 at 1 oz/A plus MSO averaged 13 g/m2 versus 74 g/m2 at the same rate alone. In addition, AC 263,222 at 2 oz/A plus MSO alone or with 28% N decreased leafy spurge dry weight by 91 and 93%, respectively, compared to only a 55% reduction with AC 263,222 at 2 oz/A alone. All treatments 10 MAT tended to decrease herbage dry weight an average of 10% compared to the control. In summary, AC 263,222 provided better control when applied in the fall compared to mid-summer. AC 263,222 plus MSO provided better leafy spurge control than AC 263,222 alone. In general, grass injury was minimal by 12 MAT regardless of treatment." |
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