Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2000
Publication Date: N/A
Citation: Interpretive Summary: We compared two new similar herbicides flumioxazin and sulfentrazone for their potential to injury soybean varieties and reduce yields. Fifteen soybean varieties that represent a wide range genetics were used in repeated greenhouse studies. We found injury from sulfentrazone was greater than injury from flumioxazin. Four of the varieties were markedly more sensitive than the other 11 varieties. We then took two of the more tolerant varieties and two of the more susceptible varieties and used them in field studies for two years to determine if the injury under field conditions caused any yield reduction. We determined early emergence and rate of emergence, as well as final stand of soybeans, compared with the untreated respective variety. In both years, both herbicides caused some injury at all rates, with injury and delay in soybean emergence being worse in one year(when we had more rainfall just after planting) than in the other year with more normal rainfall patterns. At normal use rates of each herbicide, yields were not reduced in either year, regardless of the degree of injury. At higher dosages, such as might occur with accidental overlapping of spray applications, yields of the sensitive varieties were reduced significantly. Our findings show substantial varietal difference in response to these herbicides, but also show that at normal rates of use, soybean yields will not likely be reduced. The results also show that flumioxazin provides more safety to soybeans than does sulfentrazone. These findings will be helpful to public and private sector personnel who are planning research or providing guidelines regarding soybean production and weed management.
Technical Abstract: Flumioxazin and sulfentrazone were compared for phytotoxicity on fifteen soybean varieties in a greenhouse study and four varieties in the field. In the greenhouse, injury from sulfentrazone was greater overall than with flumioxazin, 10% compared to 1%, respectively, at the normal use rates. The four varieties P9552, P91B01, P9362, and P9305 were more sensitive tolsulfentrazone than the eleven other varieties based on visual injury and plant height reductions. Visual injury symptoms consisted of stunting, crinkling of leaves, and chlorotic spots. Varieties P9305, P9306, P9352, and P9362 were compared in a field study with herbicide treatments of 105,210,and 420 g ai/ha flumioxazin or 224, 448, and 896 g ai/ha sulfentrazone with an untreated control of each variety for comparison. Emergence counts taken approximately 10 days after treatment (DAT) and stand counts at 21 days after emergence (DAE) were significantly reduced by most herbicide treatments on all varieties in 1998. The highest rate of each herbicide reduced the emergence and stand counts for most varieties in 1999. Visual injury was greater for variety P9305 than other varieties with most sulfentrazone treatments in both years and with flumioxazin in 1998. At normal use rates of each herbicide, yields were not significantly affected in either year. At higher rates, P9305 was most sensitive to the two herbicides as indicated by a reduction in yield. Rainfall immediately after applications and lower temperatures at emergency may have contributed to greater soybean injury in 1998.