Broadleaf weeds have become an increasing problem in Mid-South rice production over the last decade. The reasons for this are debatable. However, two contributing factors in Mississippi are the prevalence of the Clearfield rice system and the spread of herbicide-resistant Palmer amaranth.

Newpath and Beyond do not control hemp sesbania and volunteer soybean, which are both among the top 10 most common weeds of Mississippi rice. Most populations of Palmer amaranth in the rice-producing area of Mississippi are resistant to glyphosate and ALS-inhibiting herbicides like Newpath and Beyond. Herbicide resistance in Palmer amaranth populations in Mississippi have allowed this species to increase in importance. Consequently, Palmer amaranth is second in importance only to barnyardgrass as a weed of rice in Mississippi.

Currently, few broadleaf herbicides that exhibit soil residual activity are available for rice. Sharpen is a Group 14, or protoporphyrinogen oxidase (PPO) inhibiting herbicide, manufactured by BASF Corporation. It is labeled for fallow, preplant and preemergence application in a variety of grain crops. A preplant label for rice was approved for Sharpen in 2011; however, applications were restricted to 15 days prior to planting. Current labeling will allow in-season applications to rice in 2014.

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Sharpen efficacy in rice has been evaluated at the Delta Research and Extension Center in Stoneville since 2010. From 2012 to 2013, this research was coordinated by Garret Montgomery, a master’s student at Mississippi State University housed at the Delta Research and Extension Center. This research demonstrated that postemergence applications of Sharpen at 1 ounce per acre controlled hemp sesbania and ivyleaf morningglory as well as Aim, which is another PPO-inhibiting herbicide often applied postemergence for broadleaf weed control in rice.

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Sharpen efficacy as a postemergence treatment in rice was not impacted by the type of adjuvant in the Mississippi research. However, crop oil concentrate will be the recommended adjuvant to include with Sharpen to minimize early-season rice injury. Rice injury was observed following applications of Sharpen at two ounces per acre (twice the labeled rate), but this did not translate to delays in rice maturity or reductions in rough or milled rice yield. Rice injury following Sharpen applications was more severe when applications were made during cool and/or wet conditions.