Weed competition is a main factor limiting sweetpotato [Ipomoea batatas (L.) Lam] production. Yellow nutsedge (Cyperus esculentus L.) is a problematic weed to control due to its ability to quickly infest a field and generate high numbers of tubes and shoots. Compounding this is the lack of a registered herbicide for selective postemergence control of yellow nutsedge. Research was conducted to evaluate the bentazon dose response of two sweetpotato cultivars and one advanced clone and to evaluate the plant hormone melatonin to determine its ability to safen bentazon post emergence. Bioassays using Murashige and Skoog (MS) media supplemented with melatonin (0.232 g a.i./L and 0.023 g a.i./L) and bentazon (0.24 g a.i./L) were conducted to evaluate the effect of bentazon on sweetpotato and to determine the interactive response of the Beauregard cultivar to bentazon and exogenous applications of melatonin. Beauregard swas the most tolerant cultivar and required dosages of bentazon that were two-times higher to cause the same injury compared with other cultivars. MS media containing melatonin and bentazon showed fewer injuries and higher plant mass than plants treated with bentazon alone. These results indicate that sweetpotato injury caused by bentazon may be reduced by melatonin.

The intensive use of herbicides in agriculture has led to the appearance of resistant weed biotypes. Resistance is the inherited ability of a plant to survive following application of an herbicide dose which should be lethal. Morphophysiological weed traits help defining the risk to evolve resistance. These traits are not exclusive to the species but may be innate to botanical order, family, or genus. Four reference countries were screened about the nature of resistance-Australia, Canada, France, and the United States-and the data were used for predictions in the Brazilian scenario. Most weed species with resistant biotypes in the reference countries seem to be native to the continent. The most important botanical families with resistant biotypes in the reference countries were also among the first ones to develop resistance in these countries. There was a predominance of C3 species over C4 in the number of plant species with resistant biotypes in the reference countries. In Brazil, three orders are considered as high risk (Gentianales, Lamiales, and Solanales), besides the six already present. Furthermore, eight botanical families present superior risk to evolve resistance and for five of them (Caryophyllaceae, Polygonaceae, Rubiaceae, Convolvulaceae, and Solanaceae), resistance cases have not been reported to date in Brazil.

Poor competitive ability and limited herbicide options make weed management of Brassica crops difficult. Growers often adopt the use of transplants, which is less efficient in terms of time, material, and labor when compared with direct seeding, resulting in higher prices per unit. Seed treatment with protective compounds could decrease crop injury from preemergent (PRE) herbicides making it profitable to direct-seed Brassica plants for production. Research was conducted to evaluate the ability of three candidate safeners [24-epibrassinolide, melatonin, and ascorbic acid (AsA)] to reduce injury caused by four herbicides (S-metolachlor, pyroxasulfone, halosulfuron, and mesotrione) applied PRE on the collard green cultivar Top Bunch and turnip cultivar Purple Top White Globe. Two independent greenhouse trials were conducted at the Clemson University Coastal Research and Education Center in Charleston, SC. Visual injury of the treated plants was evaluated weekly and dry mass was collected 21 days after treatment. Seed treatment did not reduce injury efficiently caused by pyroxasulfone, halosulfuron, and mesotrione; all doses were lethal for both crops. However, collard seeds treated using melatonin and AsA had 66% and 54% less injury caused by S-metolachlor at 514 g⋅ha–1 a.i., respectively. On turnips, melatonin was the only treatment that reduced the S-metolachlor damage on seedlings, with 43% less injury than untreated seedlings. Plant injury and plant weight correlated significantly for both Brassica crops. The reduction in injury caused by S-metolachlor when seeds were treated with melatonin and AsA validated those compounds’ protective ability. Seed treatment with melatonin could be combined with PRE applications of S-metolachlor to overcome the low weed competitive ability of these species early in the season.

Due to excessive crop damage, currently, there are no selective postemergent (POST) herbicides registered for sweetpotato [Ipomoea batatas (L.) Lam] to control broadleaves and nutsedge species. Expansion of bentazon and mesotrione herbicide labels to include sweetpotato would be beneficial for growers. Two experiments were conducted. The first evaluated the dose response of sweetpotato cultivars Beauregard and Covington to bentazon (514, 1,028, and 1,542, g a.i. ha -1 ) and mesotrione (105, 210, and 315 g a.i. ha -1 ) when melatonin, 24-epibrassinolide, or ascorbic acid (AsA) were included in the tank mix. The second experiment evaluated the efficiency of bentazon and mesotrione for control of yellow nutsedge (Cyperus esculentus L.) and Palmer amaranth (Amaranthus palmeri S. Wats.), when different doses of melatonin, 24-epibrassinolide, or AsA were added to each herbicide. In the first experiment, when treated with herbicide alone, Beauregard exhibited injury levels lower than Covington for both herbicides. No injury was observed when plants were treated with plant hormones or AsA alone. At the lowest dose of bentazon and mesotrione, the addition of AsA or plant hormones in the tank mix significantly reduced percentage injury and increased plant tolerance, requiring higher doses of herbicide to cause 10, 20, and 30% injury. In the second experiment, the addition of plant hormones and AsA in the tank mix had no antagonistic effect on herbicide effectiveness, exhibiting similar levels of injuries as herbicides application alone. These results suggest that the use of plant hormones and AsA could improve sweetpotato tolerance to POST applications of bentazon and mesotrione without reducing herbicide effectiveness. INTRODUCTIONSweetpotato [Ipomoea batatas (L.) Lam] production in the United States has increased by 37.6% from 2012 to 2017, reaching an estimated value of US$654 million in 2018 (USDA,