Sequential application of herbicides for Alternanthera philoxeroides in transplanted rice fields to reduce below-ground propagules

• Published in: Journal of Weed Science and Technology Vol. 69; no. 1; pp. 8 - 18
• Main Authors: Ihara, Nozomi, Mineta, Takuya, Yoshimura, Yasuyuki, Matsuhashi, Saeko, Koarai, Akira
• Format: Journal Article
• Language: English; Japanese
• Published: The Weed Science Society of Japan 2024
• Subjects: florpyrauxifen-benzyl; herbicidal effects on below-ground propagules; pyraclonil; sequential application of two herbicides; transplanted paddy rice cultivation
• ISSN: 0372-798X; 1882-4757
• DOI: 10.3719/weed.69.8

To develop effective herbicide control methods for alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.) in the context of transplanted paddy rice cultivation, six herbicide treatments were tested in small-scale plots (2.7 m2) in 2021 and 2022. The tests were conducted in farm paddy fields in Chiba prefecture, Japan, where alligatorweed emerges naturally. Dry weights of regenerated alligatorweed from adjusted stem fragments and above- and below-ground naturally emerged alligatorweed were measured. Two types of sequential herbicides applications were determined to be effective. The first approach entailed applying pyraclonil in the post-regeneration stage of the weed, followed by the application of a mixture of florpyrauxifen-benzyl, penoxsulam, and benzobicyclon approximately 20 days after transplanting. The second approach entailed applying a mixture of imazosulfuron, oxaziclomefone, pyraclonil, and bromobutide in the post-regeneration stage of the weed, followed by florpyrauxifen-benzyl approximately 40 days after transplanting. These sequential applications reduced the dry weights of regenerated plants from stem fragments to 6% or lower compared with those in an untreated plot, while the above- and below-ground naturally emerged weeds to 8% or lower compared with those in an untreated plot. The effectiveness of the sequential applications of the two herbicides varied little depending on treatment years or targeted parts of the weed. Furthermore, 2 consecutive years of effective sequential applications in actual-scale fields of 5 a (500 m2) significantly reduced the dry weight of below-ground propagules of alligatorweed. The 2 consecutive years of the effective sequential application of herbicides enabled conventional weed management in the following year.