Greenhouse response of six aquatic invasive weeds to imazamox.

Research was conducted to evaluate the response of six aquatic invasive weeds to imazamox (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H -imidazol-2-yl]-5-(methoxymethyl)-3-pyridinecarboxylic acid). Alligatorweed, creeping water primrose, giant salvinia, parrotfeather, waterhyacinth, and water lettuce were treated with 35 to 560 g ae/ha imazamox and comparison treatments of 2240 g ae/ha glyphosate (N-(phosphonomethyl)glycine) and 560 g ae/ha imazapyr (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H -imidazol-2-yl]-3-pyridinecarboxylic acid). Based on calculated EC 70 values for dry weight reductions, weed species ranked by increasing imazamox sensitivity were giant salvinia (not calculable), water lettuce (533 g/ha), waterhyacinth (372 g/ha), parrotfeather (115 g/ha), creeping water primrose (116 g/ha), and alligatorweed (65 g/ha). Dry weights among all species were similar after treatment with 560 g/ha imazamox or imazapyr and were at least 79%, except for giant salvinia. Control of giant salvinia did not exceed 39% with imazamox or imazapyr but was 89% with glyphosate. Dry weight response of the other five species was equivalent between imazamox and glyphosate. Based on these results, five important invasive aquatic weeds were sensitive to imazamox, and future research should quantify the sensitivity under field conditions.