Florida ranks first and second as a producer of fresh market tomato (Solanum lycopersicum L.) and strawberry (Fragaria ×ananassa) crops with a total economic value of $426 and $307 million in 2019 (USDA-NASS, 2020), respectively. Weed control is a major production challenge in Florida, along with other challenges such as high production costs and foreign market competition (Guan et al., 2017; Yu et al., 2020). Yellow (Cyperus esculentus L.) and purple nutsedge (Cyperus rotundus L.) are especially problematic weed species in tomato and strawberry crops (Daugovish and Mochizuki, 2010; Yu et al., 2020). Nutsedge rhizomes grow rapidly under the plastic mulch and can produce multiple shoots in a few weeks (Webster, 2005b). Plastic mulches inhibit the emergence of grasses and broadleaf weeds but do not impede nutsedges, as their pointed shoot tips pierce plastic mulches (Gifford and Bayer, 1995; Webster, 2005b).
Several greenhouse studies have reported that nutsedge density, time of emergence, and resource competition affects the yield of tomatoes, bell peppers, and eggplants (Morales-Payan et al., 1997, 2003), whereas field studies conducted in Florida (Boyd, 2015; Boyd and Reed, 2016) reported that nutsedge growing on the bed did not reduce strawberry and tomato yield. Contrastingly, a field study reported a significant decrease in marketable yields of radish due to nutsedge interference in Florida (Santos et al., 1998). Although effects of nutsedge population on vegetable crop yields are inconsistent, uncontrolled populations spread rapidly, reduce crop quality, affect mulch integrity, and increase labor associated with harvest and mulch removal (Adcock et al., 2008; Preece and Read, 2005). Furthermore, the allelopathic effects of nutsedge tubers are known to affect the root and shoot growth of cucumbers and tomato (Alsaadawi and Salih, 2009).
A variety of PRE herbicides (may be applied on flat ground or raised beds before planting the crop) are registered in strawberry and vegetables, but none are effective on nutsedge species, and as a result, growers tend to rely on fumigants for weed control. However, fumigants are found to be more effective for long-term weed control when used in combination with herbicides applied PRE and POST (Yu et al., 2019). Several PRE herbicides, including sulfentrazone, S-metolachlor, and fomesafen, are registered in tomato and are applied on raised beds under the plastic mulch (Boyd et al., 2019; Mohseni-Moghadam and Doohan, 2017; Yu et al., 2020). However, various studies have reported that these chemicals have inconsistent effects on nutsedge control over time (Boyd and Reed, 2016; Johnson and Mullinix, 2005; Yu and Boyd, 2017; Yu et al., 2019).
Previous research has demonstrated that sulfentrazone alone applied on the top of raised beds right before installing plastic (PRE-t) did not effectively control purple nutsedge (Yu et al., 2020). Sulfentrazone was newly registered in 2016 for use in tomato and strawberry production in Florida, but how to best integrate sulfentrazone into current weed management programs is still unknown. We hypothesized that pretransplant application of sulfentrazone plus metribuzin on flat ground during fallow period and raised beds before installing plastic mulch fb halosulfuron POST directed basal application could decrease purple nutsedge establishment and provide control throughout the season.
To achieve this goal, we addressed the following objectives: 1) compare two rates of sulfentrazone to control weed populations, 2) compare single bed-top applications vs. a fallow application on flat ground 30 d before bed formation followed by applications on the bed top to control weeds, and 3) to determine the efficacy of sulfentrazone tank-mixed with other PRE products in controlling weeds in tomato and strawberry.
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