Waterhyacinth [Eichhornia crassipes (Mart.) Solms] has been the focus of national legislation efforts and has been listed as noxious, invasive, potentially invasive, or prohibited by at least seven U.S. states. Auxinic herbicides are one of the most effective control methods labeled for use in aquatic sites. In the United States, florpyrauxifen-benzyl, a synthetic auxin, was recently (2018) registered for use in aquatic sites, but limited information has been published on efficacy, especially differences between the two formulations. Therefore, the purpose of this work was to evaluate two formulations of florpyrauxifen-benzyl—suspension concentrate (SC) and emulsifiable concentrate (EC)—at three rates each (14.8, 29.5, and 58.9 g ai ha−1) for control of E. crassipes under outdoor and greenhouse conditions. All rates of each florpyrauxifen-benzyl formulation reduced E. crassipes biomass by 90% to 100% when compared with nontreated plants at 5 wk after treatment. Based on plant recovery in the outdoor trial, there was some evidence that the lowest rate (14.8 g ai ha−1) of florpyrauxifen-benzyl SC and EC may not be as efficacious at reducing E. crassipes biomass as the SC and EC formulations when applied at 29.5 and 58.9 g ai ha−1. Future work should evaluate the florpyrauxifen-benzyl rates tested in this research against E. crassipes in field trials and/or an operational setting to confirm findings.

The absorption and translocation of 14C-terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] and 14C-fluometuron [1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl) urea] in cotton (Gossypium hirsutum L. ‘SJ-1′) and snapbean (Phaseolus vulgaris L. ‘Tenderette’) were studied. 14C-terbutryn supplied to the roots accumulated in the root system of both species. However, snapbean plants (sensitive) absorbed and translocated more 14C to the shoots than cotton (tolerant), followed by rapid distribution in the leaf mesophyll tissue. In cotton, the translocated 14C-terbutryn accumulated in stems, petioles, and leaf veins. Excised cotton roots absorbed more 14C-terbutryn than excised snapbean roots. The uptake and distribution pattern of root-applied 14C-fluometuron was similar in both species. Foliar application to the primary leaf of snapbeans and to one cotyledon of cotton resulted in 2% of 14C-terbutryn transported acropetally to younger leaves with no basipetal movement. Translocation of 14C-fluometuron from the site of foliar application was two or three times faster than terbutryn with significant basipetal transport in both species.

Lanolin or lanolin + corn (Zea mays L.) starch rings are often used as barriers on leaves to prevent runoff of foliarly applied 14C-herbicide treatments. A preliminary experiment showed that 64 and 90% of the applied 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 57 and 87% of the applied glyphosate [N-(phosphonomethyl)glycine] was adsorbed to or absorbed into a lanolin and lanolin + starch ring, respectively, during 6 days on a glass slide. Absorption and translocation of 2,4-D in hemp dogbane (Apocynum cannabinum L.) was decreased from 26% down to 16 or 17% of the total applied when a lanolin or lanolin + starch ring was used. Glyphosate absorption and translocation increased with the lanolin ring but not with the lanolin + starch ring. Distribution of the translocated 2,4-D and glyphosate was also altered by use of the ring barriers. Results indicate that one should avoid use of the lanolin ring in 14C-herbicide absorption studies to simulate field conditions.

Following a precultivation with pedospheric nitrogen nutrition, nitrate or ammonium solutions were supplied to the shoots of Ricinus plants by spraying (during the experimental period) resulting in an increase of biotic/organic and abiotic/inorganic particles on the surface, which significantly increased wetting of the leaf surfaces. The distribution of particles on the surface of sprayed leaves, in particular crystals around and in stomata, indicated the possible entry of nutrients via thin water films through the stomatal pores in addition to diffusion through the cuticle. Ammonium was taken up more readily than nitrate by the foliage, but both at relatively low rates which caused N limitation. Interestingly, the inorganic N, both in the form of nitrate and even ammonium, was entirely assimilated in the shoots; phloem transport of inorganic N to the root was negligible. The flows of malate, and the acidification of the apoplastic washing solution of leaves in ammonium-sprayed plants pointed to the role of metabolism of malate and excretion of protons in maintaining pH during ammonium assimilation in the shoot. Ammonium-sprayed plants incorporated the N in the same amounts in shoots and roots, only 38% of the shoot-borne N being recycled in the xylem. In nitrate-sprayed plants the root was not only favoured in N partitioning, but even a net export of previously incorporated N from the shoots occurred which reflected the N limitation. The N limitation also affected carbon metabolism, in particular the flows of C, incorporation in the shoot and photosynthesis, which were decreased when compared with data from recent experiments with pedospheric well fed Ricinus. However, there was little difference in C flows between nitrate and ammonium-sprayed plants with respect to respiration, C partitioning and, most interestingly, in relative stimulation of root growth. The loss of C from dark respiration of the shoots was high on a f. wt basis as well as in relative terms, owing to exclusive N assimilation in the shoot. In general the plants invested untargeted increases in root growth as a result of N limitation irrespective of the imposed artificial treatment which made the shoot the site of mineral N uptake.