|Johnson, William - PURDUE UNIV|
|Nelson, Kelly - UNIV OF MO|
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: December 2, 2003
Publication Date: January 9, 2004
Citation: DONALD, W.W., JOHNSON, W.G., NELSON, K. IN-ROW AND BETWEEN-ROW INTERFERENCE BY CORN MODIFIES PREEMERGENCE RESIDUAL HERBICIDE PHYTOTOXICITY. WEED SCIENCE SOCIETY OF AMERICA ABSTRACTS. 2004. V. 44. No. 252. Technical Abstract: The presence of row crops, such as field corn, improves herbicidal control of weeds, but the impact of weed position relative to crop rows on herbicide efficacy is unknown. One research goal was to determine whether weeds emerging in corn rows responded differently to preemergence soil residual herbicides than those emerging between corn rows. A second goal was to determine whether corn yield was best described by regression on a) in-row total weed cover (b) between-row total weed cover or (c) both measured at mid-season. Preemergence atrazine + s-metolachlor + clopyralid + flumesulam were broadcast at different rates (0X, 0.25 X, 0.5 X, 0.75 X and 1 X) in field corn at two sites in Missouri, with the 1X rate equal to 2.24 + 1.75 + 0.211 + 0.067 kg ai/ha, respectively. Treatment effectiveness was measured as between-row and in-row grass weed cover (primarily giant foxtail), broadleaf weed cover (primarily common waterhemp, common ragweed, common cocklebur, smartweed species and velvetleaf), total weed cover, and corn grain yield. Total weed cover was reduced by increasing herbicide rate in a dose dependent response and was as much as 20% lower in-row than between-row at both sites. As a consequence of corn interference with grass and broadleaf weeds, less herbicide was required to reduce total weed cover to the same extent in corn rows than between rows. For example, the relative herbicide rates required for 40% total weed cover at mid-season were 34 and 69% of the 1X rate in-row and between-row, respectively, at one site and 10 and 29% of the 1X rate in-row and between-row, respectively, at a second site. At both sites, corn yield loss was best modeled versus between-row total weed cover emerging after herbicide treatment, rather than both in-row and between-row total weed cover.