Various combinations of glyphosate and 2,4-D (± surfactant) were evaluated for control of Brazil pusley [Richardia brasiliensis (Moq.) Gomez]. Typical 2,4-D symptoms on plants were manifested within 2 to 3 days after treatment. Application of glyphosate alone had only marginal effects (14%) on Brazil pusley, but the addition of Induce® (nonionic surfactant) significantly increased control to 83% and reduced the fresh weight by 68%. Application of Landmaster®II or a tank-mix of glyphosate + 2,4-D (± surfactants) resulted in 96% to 100% control. Treatment with 2,4-D alone, or with Induce®, or L-77® (organosilicone surfactant) resulted in 84%, 90%, or 100% control, respectively. Very low fresh weights of Brazil pusley were recorded when 2,4-D +Induce® or L-77®, Landmaster®II (± surfactants), or the tank-mix (± surfactants) were applied. In the regrowth studies, shoot weight was greater following application of glyphosate with or without L-77® or Kinetic® (a blend of nonionic and organosilicone) than following other treatments. The fresh weight of the shoots in the regrowth study, recorded following the application of 2,4-D or Landmaster®II (± surfactants), was very low except when Kinetic® was added to Landmaster®II. No regrowth of shoots occurred following the tank-mix treatment. Similar observations were recorded for roots. Plants treated with 2,4-D did not regrow. The presence of 2,4-D in either formulation accelerated synergistic effect of the glyphosate to the target site. Therefore, 2,4-D could be used either as a component of a formulation or in a tank-mix with glyphosate to control Brazil pusley. Chemical names used: N-(phosphonomethyl glycine) (glyphosate); 2,4-dicholorophenoxyacetic acid (2,4-D).
Glyphosate is the most widely used herbicide for postemergence weed control in Florida citrus (Citrus spp.). Variation in susceptibility of certain weed species to glyphosate has been observed in last few years. Therefore, understanding the mechanism underlying such phenomenon is required. Experiments were conducted to evaluate differences in tolerance of four weed species to glyphosate by quantifying glyphosate efficacy, the amount of epicuticular wax, absorption, and translocation of carbon-14-labeled glyphosate (14C glyphosate). The results of glyphosate efficacy study suggested that application of glyphosate at 3 oz/acre resulted in 99%, 90%, and 84% control of florida beggarweed (Desmodium tortuosum), spanishneedles (Bidens bipinnata), and johnsongrass (Sorghum halepense), respectively. Increasing application rate and addition of nonionic surfactant (NIS) usually did not improve glyphosate efficacy. Ivyleaf morningglory (Ipomoea hederacea) was the most tolerant and resulted in 0% and 25% control when glyphosate applied at 3 and 24 oz/acre, respectively. Biomass reduction in all weed species reflected a similar trend to percent control in response to all glyphosate treatments. Glyphosate absorption and translocation in the weed species were differed with the quantity of wax extracted. Ivyleaf morningglory had the lowest leaf wax content (10.8 μg·cm−2) and showed less absorption (62% to 79%) and translocation (15% to 39%) of 14C-glyphosate compared with other weed species. The absorption of 14C-glyphosate was in the range of 87%, 71% to 83%, and 72% to 83%; and translocation was 34% to 50%, 32% to 52%, and 53% to 58% in florida beggarweed, spanishneedles, and johnsongrass, respectively. Increasing glyphosate application rate from 6 to 12 oz/acre and addition of NIS usually increased 14C-glyphosate translocation.