T.M. Teynor1, D.H. Putnam2, E.S. Oplinger3, E.A. Oelke2, K.A. Kelling3, and J.D. Doll3
1Center for Alternative Plant and Animal Products, University of Minnesota, St. Paul, MN 55108.
Vernonia (Vernonia galamensis L.) or ironweed, is one of 6,500 wild plant species screened by the USDA for production of desirable seed oils. This potential oilseed crop is native to eastern Africa. There are over 1,000 species in the genus ranging from tropical herbaceous species to North American shrubs. Another vernonia species, V. anthelmintica Willd., was evaluated earlier during the 1950s for its vernolic (epoxy) acid content. Consistent problems with seed shattering, disease, and low yield of vernolic acid resulted in an end to further agronomic and breeding studies on this species. Developmental research on use of the oil and vernolic acid from Vernonia species has been conducted since the 1960s.
Vernonia seed contains about 40 to 42% oil of which 73 to 80% is vernolic acid. This is about 30% more vernolic acid than the best varieties of V. anthelmintica. Products that can be made from vernonia include epoxies for manufacturing adhesives, varnishes and paints, and industrial coatings. The low viscosity of vernonia oil would allow it to be used as a nonvolatile solvent in oil-based paints since it will become incorporated in the dry paint rather than evaporating into the air. Consequently, it is possible that emissions associated with photochemical pollution can be reduced by up to 160 million pounds per year if this crop is fully exploited.
Vernonia could also serve as a natural source of plasticizers and stabilizers (binders) for producing polyvinyl chloride (PVC plastic), which currently is manufactured from petroleum. The potential use of vernonia as a petroleum substitute is important since the demand for petroleum each year in the USA is approximately 8,500 pounds per person, of which about 500 pounds per person is needed for production of plastics and industrial petrochemicals. Some vernonia species have been reported to have medicinal properties.
Vernonia is an annual, herbaceous plant in the Compositae (Daisy) family. This plant will not flower until the daylengths are shorter, which is typical of most tropical plants. Plants are thornless and vary in height and number of flowers. Plant habits vary from those that are 8 in. tall with a single flower head, to those with vigorous, shrubby plants with multiple stems and flower heads that may reach 9 ft in height. The stems do not branch until after the terminal flower head is formed. The lavender terminal flowers, and lateral flowers that develop in the uppermost leaf axils, have a thistle-like appearance. If sufficient moisture is present for continued growth, the lateral branches with secondary flower heads will grow above the first-formed flower head. Brown seeds develop in seed heads that are 1 in. in diameter. Leaves are alternate and sessile, and have toothed margins with taper-pointed tips and wedge-shaped bases. Leaves are 1/4 to 2 in. wide and up to 10 in. in length. In Zimbabwe (southern Africa) the crop requires five to seven months from planting seed to harvest. However, in Zambia (central Africa) the seed was mature four months after planting. Plants observed by Gilbert (1986) in eastern Africa were shorter (8 in.) and apparently matured much earlier than four months after germination.
Vernonia is a crop adaptable to the latitudes within 20 degrees north or south of the equator since this comprises its natural distribution. It has also been grown successfully in Pakistan, which indicates a broader adaptation. Hawaii, Puerto Rico, and the semiarid areas of the subtropics and tropics, such as in Africa, Central and South America, Australia, and India, would be suitable growing regions. This crop is adaptable to areas with as little as 20 in. of annual rainfall. Sufficient moisture must be present to establish good stands and permit the first flower heads on each stem to mature. But rainfall levels that allow secondary flower heads to develop will result in poor uniformity of seed maturation and seed shattering during subsequent rainfall or harvesting.
The effort to develop this species as a new crop must concentrate on production areas where a short rainy season occurs during a period of four, or at most five months, to promote good growth and flowering. The subsequent period for seed development and maturation should have one or two months when there is very little or no precipitation. Dry conditions promote seed retention. It seems that natural selection has favored a plant type in vernonia that does not disperse seed at maturity, but rather will retain it until rainfall is adequate for germination and growth of the seedlings. Rainfall pattern is evidently more important than total amount for maximum productivity of vernonia.
Porous, well-drained soils are required to grow this crop successfully. Field trials in Zimbabwe on well-drained soil found that plants grow erect with a single stem until the first flower head appears, after which lateral branches develop. However, on poorly-drained soils the terminal growth stops before flowering and the upper portion of the plant dies. Branches will subsequently grow from the base of the plant, but also wither and die without flowering. Soil with intermediate drainage will produce plants that develop a few flower heads, but with very low seed yields.
Seeds germinate quickly, but seedling vigor is poor. A western African variety from northern Ghana has vigorous seedlings and could be used in developing varieties with better seedling vigor.
Considerable agronomic research was conducted on V. anthelmintica in the 1960s and 1970s. Research on this species was stopped when yields continued to be low due primarily to poor seed retention. Agronomic studies on V. galamensis began in Zimbabwe during 1983, which are currently unpublished. These studies used the unimproved, yet very uniform germplasm from Ethiopia. Additional vernonia germplasm is being collected in Zimbabwe for future evaluations.
Since seed of vernonia is relatively small, a firm, level seedbed with few weeds should help promote the rapid establishment of a good stand as with most crops.
A seeding-date trial to determine the best planting time was conducted in Zimbabwe during 1985-1986. Seed was sown at mid-month from December to April, which is comparable to June through October in the northern hemisphere. All plants flowered and produced mature seed. The plot seeded in December flowered when plants were almost 9 ft tall, while the last plot seeded in April had flowering plants that were only 3 ft tall. This study indicated that later planting dates are preferred, if the number of frost-free days in the growing season will permit it.
Preliminary results of unpublished research on the effect of plant spacing conducted in Zimbabwe during 1985 and 1986, and continued in 1987 were inconclusive. More information was deemed necessary before reliable conclusions could be drawn.
Studies on the response to fertilizer were also performed in Zimbabwe, but will not be reported until further research is conducted in this area.
Varietal development for vernonia is still in the early stages. Wild types of vernonia are still being collected to obtain sufficient genetic resources to develop more productive varieties. No released varieties of V. galamensis have been reported.
Weed control after germination is a problem due to the poor seedling vigor. Recommendations for weed control by cultural or chemical methods are not currently available. No herbicides are currently cleared for use in vernonia.
No serious disease problems as yet have been reported for vernonia.
Insect damage has not been reported in research trials.
A standard harvesting method has not been reported. Perdue et al. (1986) mentioned that seeds will stay on plants for 30 or more days after ripening. Growers can therefore wait until most of the seeds are ripe before harvest, which is especially important when seed ripens unevenly among plants. More uniform ripening of the seeds was discovered to occur when plants were "topped" earlier in the growing season, that is, pruned back to a height of 6 in. above the ground. This practice promotes production of many lateral branches that tend to flower and develop seed at the same time, which results in more uniform ripening of seeds and a shorter time from planting to maturity.
Specific procedures for the drying and storage of vernonia have not been determined.
Vernonia has limited possibilities as an oilseed crop for the northern continental United States. This crop flowers and sets seed too late in the growing season because shorter days are required for flower initiation and development. Frosts follow flowering too quickly to allow complete seed development and maturation. Trial plantings conducted at Experiment, Georgia in the 1960s produced few flowers and no seed. Trials planted in greenhouses in Glenn Dale, Maryland flowered in November and seed matured in December, which is much too late for a field crop in that area. Failure of vernonia to produce a mature crop in preliminary field trials was due most likely to unsuitable environments with excessive moisture, poorly drained soil and/or insufficient length of growing season.
However, a variety was found in Nigeria during the 1980s, at about 11 degrees north and south of the equator, which flowers about six weeks earlier than any plants found previously. If a variety can be found that flowers early enough in the United States to allow for maturation of the seed, does not shatter readily, and is resistant to disease and insect problems, then this oilseed crop may be suitable for the Southwest when planted in late summer or early fall. Areas that do not have a well-defined, severe dry season and soils without good drainage should be avoided. On the other hand, Perdue (personal communication, 1991) did not feel there was good potential for growing vernonia in the southwestern USA due to low and variable yields. This crop is clearly not adapted or recommended for the Upper Midwest. Tropical and subtropical areas would be climates in which this potential oilseed crop could be grown.
Seed yields improved from 1,627 to over 2,200 lb/acre in Zimbabwe during 1986 to 1987. The yield of vernolic oil in the Zimbabwe trials (1987) was 891 lb/acre, which would mean that about 365,000 acres of vernonia would need to be planted to supply the solvent needs for the production of alkyd-resin paint in the United States. This production figure does not include the needs for paint production in other countries and the possible demands from other uses of vernonia oil. Researchers have indicated that seed yields can be doubled or tripled with better cultural practices and by breeding for improved varieties after more wild germplasm is collected and made available to plant breeders. Additional agronomic and utilization research on V. galamensis needs to continue before it can be established as a new crop.
The current market for vernonia is small. Utilization research for vernonia has shown there are at least three areas with strong potential markets: (1) as a plasticizer and stabilizer for polyvinyl chloride - a current market, (2) a component in protective coatings, and (3) use in interpenetrating polymer networks with polystyrene to make unique plastics. The best potential market for this crop in the near future is in development of epoxy coatings. By bringing the oil or seed to the international market, even if in small quantities, the agricultural sector would prove it can provide a reliable supply of seed. It has also been suggested that the oil should be extracted from the seed and refined in the producing countries before export, in order to realize a higher price for the product, and reduce shipping costs. Vernonia will not be considered seriously as a new industrial crop until a vernonia product is in commerce and agriculture has shown it can produce a reliable supply at a reasonable cost.
The information given in this publication is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no endorsement for one product over other similar products is implied by the Minnesota and Wisconsin Extension Services.