Herbicide tolerance by vernonia grown in the temperate zone

Abstract

Vernonia galamensis (Cass.) Less., a plant of semi-arid, equatorial origin, has significant quantities of epoxy fatty acids in its seed oil. This vernolic fatty acid has potential use in alkyd resin and oil-based paints and coatings formulations with low volatile organic compound emission. Improved agronomic practices are needed to commercialize vernonia in the temperate zones. Vernonia must be planted in the spring in temperate latitudes because it is not frost tolerant. Thus, it must compete with aggressive summer annual weeds during its germination and early vegetative growth period. Once established, vernonia is vigorous and can compete against weeds, but weed control is very critical when the vernonia plants are young. To avoid the high cost of hand weeding, identification and registration of appropriate pre- plant incorporated (PPI), pre-emergence (PRE), or early post-emergence (POST) herbicides are necessary. Two years of herbicide studies in the field and greenhouse have identified the reaction of vernonia to PPI, PRE, POST, and layby (LAY) herbicides in terms of tolerance and non-tolerance. Information about non-tolerant herbicides is essential since vernonia, in some cases, may pose a threat as a new crop weed. Based on the conditions of these experiments, herbicide compounds that appear to be excellent candidates for registration include, PPI: trifluralin, benefin, ethalfluralin, and pendimethalin; PRE: pendimethalin, DCPA, metolachlor, napropamide; POST: fluazifop, pronamide, and sethoxydim; LAY: pendimethalin and DCPA. Rates and timing of application are very important for some materials. A potential, but less likely, herbicide includes PRE: propachlor. Materials that have little or no potential as herbicides for vernonia production include the following: PPI: EPTC; PRE: metribuzin, oryzalin, atrazine, and diuron; POST: clopyralid, bromoxynil, dicamba, oxyfluorfen, 2,4-D, and 2,4-DB. In addition to crop tolerance, the usefulness of a given herbicide will also depend on weed species that are competitors at a specific crop location.