Cranberry Response To Sulfentrazone Rate, Timing, And Application Volume

The recent registration of sulfentrazone, a selective, soil-applied, PRE herbicide labeled for control of various weeds in cranberry, expanded the number of modes of action that could be used in the crop. A 2018 preliminary study in Massachusetts showed that high rates of sulfentrazone applied at the cabbage head stage reduced the number of flowering uprights (vertical stems) without impacting the final yield. To clarify the use patterns needed to promote crop safety when using sulfentrazone, six studies were conducted in New Jersey and Massachusetts in 2019 and 2020. Studies compared sulfentrazone applications made at two timings (spring dormant, SD; or cabbage head [CH] stage), two rates (280 and 420 g ai ha(-1)), and three application volumes simulating either chemigation (3,740 L ha(-1)) or boom application (190 L ha(-1) alone or followed by 0.25 cm water wash-off). Boom application studies in New Jersey in 2018 and 2019 did not show significant long-lasting injury (necrosis or stunting). However, a comprehensive observation of cranberry uprights 8 wk after treatment showed a high rate of terminal bud necrosis, a reduction in the number of reproductive structures, and the development of axillary shoots associated with a high rate of sulfentrazone applied at CH. A mitigation study conducted in 2019 and 2020 confirmed the safety of chemigated sulfentrazone at the high rate with no yield reduction, regardless of crop stage at application. Washing off the herbicide from the cranberry canopy immediately after boom application did prevent the necrosis of terminal bud and the related development of nonproductive secondary shoots. Considering the results of this study, application of sulfentrazone over the top of cranberry vine before scales of the terminal bud start loosening would be prudent practice at this time.