Florida strawberry growers apply the nonselective herbicide paraquat for crop termination. Alternative herbicides are desirable because of recent label restrictions on paraquat use and the occurrence of three paraquat-resistant weed species found in strawberry fields. Field experiments were conducted at the Gulf Coast Research and Education Center at Balm, FL, to compare the efficacy of diquat, paraquat, and glufosinate and determine the optimal rate for strawberry termination. Peak control occurred at 14 d after treatment and strawberry foliage desiccation increased as herbicide rate increased. The highest rate of diquat (2,240 g ai ha−1) and paraquat (2240 g ai ha−1) provided 59% and 79% strawberry control, respectively, and 39% and 77% strawberry foliage desiccation, respectively. The highest rate of glufosinate (2,624 g ai ha−1) provided 82% and 84% strawberry control and desiccation, respectively. Regression analysis determined the rates required to provide 50% strawberry control measured 1,100, 650, and 550 g ha−1 for diquat, paraquat, and glufosinate, respectively, whereas the rates required to provide 80% strawberry control were greater than 2,240 g ha−1 for the first two herbicides and 2,020 g ha−1 for glufosinate. Herbicide rates required to provide 50% strawberry foliage desiccation measured 480, 550, and 330 g ha−1 for diquat, paraquat, and glufosinate, respectively, whereas the rates required to provide 80% strawberry foliage desiccation were greater than 2,240 g ha−1 for the first two herbicides and 1150 g ha−1 for glufosinate. Overall, these results indicate glufosinate is the most effective herbicide for strawberry termination, whereas diquat is the least effective herbicide.

Research was conducted from 2013 to 2015 across three sites in Mississippi to evaluate corn response to sublethal paraquat or fomesafen (105 and 35 g ai ha−1, respectively) applied PRE, or to corn at the V1, V3, V5, V7, or V9 growth stages. Fomesafen injury to corn at three d after treatment (DAT) ranged from 0% to 38%, and declined over time. Compared with the nontreated control (NTC), corn height 14 DAT was reduced approximately 15% due to fomesafen exposure at V5 or V7. Exposure at V1 or V7 resulted in 1,220 and 1,110 kg ha−1 yield losses, respectively, compared with the NTC, but yield losses were not observed at any other growth stage. Fomesafen exposure at any growth stage did not affect corn ear length or number of kernel rows relative to the NTC. Paraquat injury to corn ranged from 26% to 65%, depending on growth stage and evaluation interval. Corn exposure to paraquat at V3 or V5 consistently caused greater injury across evaluation intervals, compared with other growth stages. POST timings of paraquat exposure resulted in corn height reductions of 13% to 50%, except at V7, which was most likely due to rapid internode elongation at that stage. Likewise, yield loss occurred after all exposure times of paraquat except PRE, compared with the NTC. Corn yield was reduced 1,740 to 5,120 kg ha−1 compared with the NTC, generally worsening as exposure time was delayed. Paraquat exposure did not reduce corn ear length, compared with the NTC, at any growth stage. However, paraquat exposure at V3 or V5 was associated with reduction of kernel rows by 1.1 and 1.7, respectively, relative to the NTC. Paraquat and fomesafen applications near corn should be avoided if conditions are conducive for off-target movement, because significant injury and yield loss can result.

Weed management is often difficult and expensive in organic production systems. Clove oil is an essential oil that functions as a contact herbicide and may provide an additional weed management tool for use on organic farms. Burning nettle, purslane, and rye responses to 5, 10, 20, 40, and 80% v/v clove oil mixture applied in spray volumes of 281 and 468 L/ha were examined. Log-logistic curves were fitted to the nettle and purslane data to determine the herbicide dose required to reduce plant dry weight 50% (GR50) and 90% (GR90). A three-parameter Gaussian curve was fitted to the rye data. The GR50 and GR90 were largely unaffected by spray volume. Nettle dry weight was reduced by 90% with 12 to 61 L clove oil/ha, whereas 21 to 38 L clove oil/ha were required to reduce purslane biomass to the same level. Rye was not effectively controlled by clove oil. Clove oil controls broadleaf weeds at high concentrations, but its cost makes broadcast applications prohibitive, even in high-value vegetable production systems.