2017 Volume 62 Issue 2 Pages 25-35
Field studies were conducted in Hiroshima Prefecture in 2014 and 2015 to evaluate the sequential application of herbicides for control of red morningglory (Ipomoea coccinea) in narrow-row (30 cm), late-planted soybean. The critical weed-free period ended by the fifth trifoliate leaf stage of soybean at the latest. The sequential application of dimethenamid/linuron mixture or flumioxazin plus alachlor as pre-emergence herbicides, followed by post-emergence application of bentazone plus quizalofop-ethyl at the second trifoliate leaf stage, and finally post-emergence directed application of glufosinate as at the fifth trifoliate leaf stage, suppressed I. coccinea dry weight to < 4 g m−2 under conventional tillage. Bentazone application provided insufficient control of I. coccinea but suppressed its growth, which limited plant growth above the spraying height during subsequent application of glufosinate. Thus, the three herbicide applications that included bentazone decreased dry weight of I. coccinea to only 1–5% of the two herbicide applications without bentazone. Total emergence and mean plant height of I. coccinea under strip tillage at high soil bulk density (1.3 g cm−3) were suppressed by 6–55% and 42–73%, respectively, relative to conventional tillage. Therefore, in high soil bulk density, the sequential application of dimethenamid/linuron mixture or flumioxazin plus alachlor as pre-emergence herbicides followed by a post-emergence directed application of glufosinate at the fifth trifoliate leaf stage of soybean suppressed I. coccinea dry weight to < 7 g m−2, which is comparable to conventional planting with three herbicide applications. These findings suggest that the number of herbicide applications to control I. coccinea can be reduced at high soil bulk density.
