Understanding the persistence of PRE-applied pendimethalin is important in determining timing of subsequent weed management programs in sugarcane on organic soils in the Everglades Agricultural Area (EAA). Dissipation of oil- and water-based pendimethalin formulations applied PRE at 2, 4, and 8 kg ai ha−1 were compared in 2011 and 2012 on organic soils in the EAA. The rate of dissipation of both formulations was very similar. Both formulations had an initial rapid rate of dissipation followed by a slower rate of dissipation. However, the initial amount of pendimethalin in the soil was higher with the water-based compared to the oil-based formulation, most likely because of the lower volatility of the water-based formulation. The half-lives (DT50s) of the oil-based formulation were 32, 18, and 10 d and 8, 8, and 12 d at 2, 4, and 8 kg ha−1, respectively, in 2011 and 2012, respectively. The DT50s of the water-based formulation were 20, 13, and 10 d and 12, 12, and 14 d at 2, 4, and 8 kg ha−1, respectively in 2011 and 2012, respectively. These DT50 values were attributed to low soil water content as well as the absence of incorporation following application. Our results suggest that dissipation of pendimethalin is rapid on organic soils irrespective of the formulation when applied under dry soil conditions with no incorporation into the soil.

Giant reed has been proposed as a bioenergy crop in the sugarcane production region of south Florida, where it has a high invasive potential. In an effort to limit future invasion of giant reed escapes in sugarcane, currently labeled sugarcane herbicides asulam and trifloxysulfuron were evaluated for its management. Greenhouse and field dose–response studies were conducted at the Everglades Research and Education Center in Belle Glade, FL, between 2010 and 2011. Herbicides were applied at rates ranging from 0.46 to 7.4 kg ha−1 asulam and 2 to 32 g ha−1 trifloxysulfuron, which represent 0.125× to 2× sugarcane labeled use rates, respectively. In the greenhouse, asulam and trifloxysulfuron reduced giant reed relative shoot dry weight by a maximum of 50% at 21 d after treatment (DAT). The probability of giant reed resprouting 35 d following herbicide treatment was greater for trifloxysulfuron when compared with asulam. In the field, it was predicted that a maximum of 69 and 55% giant reed control occurred with application of asulam and trifloxysulfuron, respectively, at 14 DAT. Relative shoot dry weight of giant reed treated with asulam and trifloxysulfuron was reduced by a maximum of 43% at 42 DAT. Application of asulam and trifloxysulfuron did not provide complete control of giant reed at twice the labeled sugarcane use rate, indicating that control of established giant reed in sugarcane with currently available herbicides would not be an option.

Elephantgrass has been proposed as a potential feedstock for biofuel production in south Florida. To limit future invasion of escapes in sugarcane and vegetables, the response of newly established elephantgrass to glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron was determined using dose–response curves. Log-logistic models were used to determine the herbicide dose required to produce 90% growth reduction (GR90). The GR90 values for shoot biomass at 21 d after treatment (DAT) were 477 g ae ha−1 of glyphosate, 262 g ai ha−1 of clethodim, 381 g ai ha−1 of sethoxydim, 12 kg ai ha−1 of asulam, and 94 g ai ha−1 of trifloxysulfuron. The GR90 values for root biomass at 35 DAT were 570 g ae ha−1 of glyphosate, 257 g ai ha−1 of clethodim, 432 g ai ha−1 of sethoxydim, 17 kg ai ha−1 of asulam, and 183 g ai ha−1 of trifloxysulfuron. Elephantgrass was predicted to exhibit 97, 98, 75, 1, and 5% mortality after application of glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron, respectively, at the label use rates 35 DAT. Results suggest that glyphosate and clethodim will provide control of newly established elephantgrass at label use rates for spot treatments and in vegetables, respectively. Rates higher than the label use rate of sethoxydim will be required to provide acceptable control of newly established elephantgrass in vegetables. However, newly established elephantgrass was not controlled by asulam and trifloxysulfuron at label use rates, implying that control of escapes will be difficult in sugarcane.