Weed Control With Preemergence Herbicides in Azuki Bean

Three field experiments were completed over a three-year period (2019 to 2021) in Ontario, Canada to develop weed management programs in azuki bean with herbicides (pendimethalin, S-metolachlor, halosulfuron, and imazethapyr) applied alone and in combination, and metribuzin, applied preemergence (PRE). At 2 and 4 weeks after emergence (WAE), there was ≤ 8% azuki bean injury from the herbicide treatments evaluated, with the exception of the treatments that included S-metolachlor which caused up to 19% azuki bean injury. Pendimethalin (1080 g ai ha-1) and S-metolachlor (1600 g ai ha-1) controlled green foxtail 83-94% but provided poor control of common lambsquarters, wild mustard, redroot pigweed, common ragweed, and flower-of-an-hour. Imazethapyr (75 g ai ha-1) controlled common lambsquarters, wild mustard, redroot pigweed, and flower-of-an-hour 90-100% but provided 76-82% control of common ragweed and green foxtail. Halosulfuron (35 g ai ha-1) controlled wild mustard 100%, common ragweed 81-84%, common lambsquarters 77-83%, flower-of-an-hour 72-75%, redroot pigweed 59-72%, and green foxtail 19-23%. The tankmix of pendimethalin + S-metolachlor controlled green foxtail and common lambsquarters 87-97% but the control was only 23- 83% on wild mustard, redroot pigweed, common ragweed, and flower-of-an-hour. The tankmixes of pendimethalin + imazethapyr and pendimethalin + S-metolachlor + imazethapyr provided 90-100% control of common lambsquarters, wild mustard, redroot pigweed, flower-of-an-hour, and green foxtail, and 78-87% control of common ragweed. The tankmixes of pendimethalin + halosulfuron and pendimethalin + S-metolachlor + halosulfuron controlled common lambsquarters and wild mustard 91-100%, green foxtail 76-95%, flower-of-an-hour 70-94%, redroot pigweed 68-91%, and common ragweed 78-79%. Metribuzin (280 g ai ha-1) controlled common lambsquarters, wild mustard, redroot pigweed, common ragweed, flower-of-an-hour, and green foxtail up to 94, 98, 81, 58, 98, and 61% respectively; control improved to 99, 100, 97, 84, 99, and 83%, respectively when the rate was increased to 560 g ai ha-1. Generally, weed density and dry biomass reflected the level of weed control. Weed interference reduced azuki bean yield by 91% in this study. Generally, azuki bean yield reflected the level of weed control.