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HORTICULTURE  -  Specialty Crop Production + Physiology

Robert Dufault
Robert J. Dufault
Professor of Horticulture + CREC Interim Director

Updated 11 January, 2008

E-mail to Prof. Dufault 

Description of Duties

My appointment is 100% research in specialty food crop physiology and culture at the Coastal Research  and Education Center in Charleston.  Specialty food crops are characterized as high value commodities that are not subsidized by the federal government (wheat, feed grains, oilseeds, cotton, and rice) and can be classified into one or more of the following nine categories:

●Ethnically-significant crops, such as immigrant crops of European, Asian, Chinese, Latino origins, etc. that are novel or exotic to the region.

●Niche crops produced to capture vulnerable market windows in season or out of season, such as forced strawberries for Thanksgiving/Christmas season, forced summer/fall asparagus, etc.

●Boutique crops are high value crops requiring only small acreage to satisfy market demands ( i.e. medicinals), etc.

●Non-plant food commodities, such as aquaculture, small scale livestock (i.e. goats, baby beef, home flock poultry), etc.

●Unusual quality crops, such as organically-grown and/or phytochemically-nutritious and functional foods.

●Unusual varieties, such as heirloom vegetables, uncommon melons, tomatoes, peppers, apples, lettuce, B size potatoes, etc.

●Crops with substantial farm value-added, such as crops grown for special bottled relishes, aromatherapy, grapes for winery, etc.

●Ordinary crops (or unusual crops) grown using unique and highly specialized cultural practices, such as use of colored mulches, season extension with row covers and organically-grown, hydroponics, baby vegetables, etc.

● Intensively-managed crops, such as most fruits and vegetables.

 

For many years now, serious financial problems have forced many farmers into deep debt or even out of the farming business.  The search for specialty crops with greater revenue potential has become a major research emphasis in universities across the country.  Crops with the greatest economic value and climatic adaptability are needed to supplement the vegetable growers' traditional crop mix to insure a continuing income. Diversity of crop production is critical for a grower to survive “putting all his eggs in one basket”. Since graduating from Kansas State University in 1982, I have been worked professionally in vegetable physiological and cultural research on traditional and nontraditional crops in Minnesota, Texas, and South Carolina.  Each position has had different problems to solve, but my task in all cases was to develop a broader database on the feasibility of improved production practices of new crops to suit the climate unique to those areas and to provide new choices for growers.

Presently, most of my time is devoted to research on specialty food crop crops production, especially determining cultural practices for organic vegetables and forcing strawberries for Thanksgiving/Christmas/New Year’s holiday season.

My philosophy  in working with specialty food crops more than with traditional crops is that with ever mounting difficulties with the marketing of our traditional crops, like fresh market tomatoes, tobacco and row crops, growers are searching for more lucrative alternatives.  I feel that it is critical that more efficient production practices of these new crops, whether they use conventional or organic cultural approaches, need to be worked out thoroughly in our unique climate before the need arises. These research findings could be used to reduce risk to a very low level and avoid trial and error on the farmers' part which could mean financial hardship. Also, with "home-grown" research, growers can immediately begin production in a well-educated, directed manner. Extensive field research projects have identified as many of the potential problems of growing these crops and then developed cultural solutions to “get around” these pitfalls. 

 

Present Research Direction
  • To investigate and refine season extension and forcing fall/winter strawberries in high tunnels with photoselective nets for the Thanksgiving/Christmas/New Year’s holiday season.
  • Develop organic nutrient solutions to prescription feed organically grown vegetables and determine if organic vegetables are more nutritious (elemental content, antioxidants, phenols, etc) than conventionally-produced vegetables.

Rationale For Current Research Thrust In Organic Farming

 

Public awareness of the need for healthier foods has led to an increased demand for highly nutritious organic vegetables resulting in one of the fastest growing agricultural markets in the U.S.  There is an apparent and prevalent public opinion that organic foods are always more nutritious and “safer” than conventionally grown foods.  The science to either prove or disprove this opinion is questionable and more research is desperately needed to clarify this situation since conventional agriculture is considered a menace by some audiences. In order to conduct fair comparisons at the “grass root level”, organic and conventional produce need to be grown with similar nutrient levels for plant growth for a valid comparison.  Organic fertility is usually supplied by applying solid composted plant +/or animal matter. “Compost” rarely has the same nutrient content from lot to lot and because of that unreliability, precision commercial recommendations are difficult.  Compost is an “adjective” not a “noun” because there are many different types of composts and they all are different nutritionally.

 

It is difficult at present to produce organic crops on a large scale on infertile sands common in coastal SC using solid composts. In every case, the goal in commercial farming, whether organic or conventional should be, supply fertilizer exactly when the crop needs it. Nutrient deficiencies are common with organic crops because of slow fertilizer mineralization rates which become especially critical as the plant nears harvest. At present, comparison of the nutritional quality of conventional and organic vegetables is impaired since fertilizer composition and availability are radically different between organic and conventional systems.  In our research, we attempt to develop new methodology that will blend the best of conventional fertility cultural practices using organic nutrients fertigated according to plant need using drip irrigation systems. At present, there are not any organic fertilizers supplying plant available nitrates that can be delivered through drip irrigation systems.  Our research objective is to develop new methods of prescription feeding crops with organic nutrient solutions that we will bio-engineer in the lab for field use.  Once these new systems are developed, fair tests of the superiority of either organic or conventional vegetables may be possible and appropriate.

 

Another advantage of our research is that more and more conventional farmers are transitioning to organic production. These farmers have used prescription feeding before with synthetic fertilizers and with our newly developed technology, they will now be able to grow crops more predictably and efficiently, now organically, using organic nutrient solutions.  There has been an increase in grower demands for organic based nutrient solutions to grow precisely nutritionally enriched vegetable.  This is a growing area of research and development in the fertilizer industry.  For the organic industry to grow and produce the quantity of crops expeditiously, better cultural practices are grossly needed to meet the ever-increasing demand for nutritious yet reasonably priced organic produce.

Rationale For Current Research Thrust In Forcing Strawberries In High Tunnels

 

In the U.S. from November through February, there is a lucrative market for strawberries since domestic supply is low and demand is high. During this time, unit price for strawberries is at its highest point during the year. Forced strawberry yields are far lower than traditional spring harvests and increasing this parameter would provide greater profitability. Environmental manipulation provides viable choice for crop improvement and the roles of light intensity, photoperiod, and temperature on strawberry production have been well investigated. Information on the effect of light quality is minimal, since light quality alteration is difficult under field conditions. The research proposed here will test the feasibility of using new technological approaches---photoselective nets, for manipulating quality of incident solar irradiation under field conditions to improve productivity and nutritional quality of forced strawberries in high tunnels. In relation to the value of holiday berries, there appears to be much room and potential to produce these very high value holiday berries in South Carolina during the holiday season rather than depending on berries from other states.

 

Physiological processes from seedling emergence to fruit production depend on both light quantity and quality. Manipulation of light for agricultural purposes has included (i) colored mulch; (ii) photoselective films; and (iii) photoselective nets. The first approach is based on reflecting light from the soil back to plants, while the second and third approaches deal with filtering sunlight to plants. The use of filters to change spectral distribution of the natural sunlight may directly influence photosynthesis by changing light absorption and/or the quantum yield of photosynthesis. Information on the effect of light quality is minimal, since light quality alteration is difficult under field conditions. The research proposed here will test the feasibility of photoselective nets and films, for manipulating quality of incident solar irradiation under field conditions to improve productivity and nutritional quality of forced strawberries in high tunnels. In my research, I will use photoselective nets called ChromatiNets. ChromatiNet® (Polysack, Inc, San Diego, CA) are a series of colored nets with special optical properties which improve the utilization of solar radiation by agricultural crops. ChromatiNet® enables growers (especially with ornamentals) to control vegetative growth characteristics, such as leaf size, branch length and plant height in plants, as well as the rate of maturation and flowering. This enables adaptation to market preferences, with clear economic advantages. These nets manipulate light quality composition, scatter light throughout the plant canopy and the transmitted light is composed of a mixture of natural, unmodified light passing through holes and spectrally-modified light passing through threads. These nets are available in a variety of shading intensities for use during the heat of summer (highest shading) or in winter (lowest shading). The nets vary in color and general activity on plants. Red nets increase vegetation and enhance earlier flowering, Yellow nets increase only vegetation, Pearl nets increase branching, Blue nets increase dwarfing and are used more with ornamentals. In an experiment in Israel, Red, Yellow, Pearl, Blue, Gray and Black nets were placed in early March over high tunnels open on the sides to allow good ventilation and bee activity.

 

 

Completed Research Highlights

 Asparagus - Summer forcing versus normal spring production - Domestic production of asparagus in the United States usually occurs from January to July with imports increasing from late summer through fall and early winter. Recently, Peru has dominated the US import market and produces asparagus year round. Forcing asparagus in late summer/fall may provide a lucrative niche enterprise for local growers. Short lifespan is a major problem with asparagus harvested in the spring in our area since excessive harvesting early in the lifespan, reduces yields and quality. Summer-forced plants, in contrast, yielded better and lived longer than those spring-harvested. Yield depends on the availability of accumulated carbohydrates in the storage roots produced by the fern in the previous season before spear harvest. Asparagus ferns’ growing season after spring harvest in coastal South Carolina lasts more than seven months. This “old” fern does not efficiently produce carbohydrates. Yearly repetitions of harvests and leaving old fern on plants throughout the late summer/fall can dangerously deplete stored root carbohydrates, reduce plant vigor, stand, yield and ultimately lifespan. The reason summer forcing systems work is that removal of old fern by midsummer allows new efficient fern to produce carbohydrates in the fall for storage and use the following spring.

Asparagus production in the humid southern States needs to be done differently than in the temperate northern States. Spring harvesting is more successful in the South if the grower mows down old fern by August 1st each year. New efficient fern will grow and produce carbohydrates for spring harvest in the late summer and fall.  Spring harvested fields should never be summer-forced and summer-forced fields should never be spring-harvested too.  If both types of production are desired, separate fields dedicated to spring harvesting and separate fields for summer forcing need to be planted.  Harvesting both in spring and again summer forcing is sure death for an asparagus field. The scheme for spring harvesting is: In the first year, plant crowns and encourage fern growth in the growing season. In year 2, do not harvest, but continue to grow large vigorous fern and in the 3rd year, the first limited harvest can begin. Spring asparagus can be harvested daily for 4, 5, 8, 10 weeks in year 1 through 4, respectively. Critical to successful spring asparagus production, fern has to be mowed down about mid-summer. Therefore, beginning in year 2 after planting crowns, each summer on August 1st, all the fern needs to be mowed down to get rid of old fern and replace it with new efficient fern. If a grower wants to try summer forcing, they should follow these guidelines:  In the first year, plant crowns and encourage fern growth in the growing season.  In year 2, do not harvest, but continue to grow large vigorous fern.  In the 3rd year, the fern is allowed to grow in spring and the first limited harvest can begin on August 1st. To induce the asparagus into production, the fern is mowed down and within 5 days, spears will emerge. Summer forced asparagus should be harvested 2, 3, 4, and 6 in the first through fourth years, respectively. The key to successful asparagus production, whether spring-harvested or summer-forced is 1: to diligently “grow” the fern after the harvest season to “make the crop” for the following year; and 2) do not over harvest the crop even though the price is excellent…over harvesting will reduce yield the following year.

With these new, mature techniques, growers can begin to consider the economic feasibility of producing asparagus off-season in coastal SC as well as the standard spring crops. Spring production, coupled with summer and fall production schemes allows production from February to October.

Clover “living mulches” for weed control in organic production Herbicides are not labeled for medicinal crops or organic vegetables and besides tractor cultivation, weed control in these crops has to be done by hand and that is costly. Our objective has been to determine the best candidates for organic weed control by using living mulches. These crops are grown in the areas between plastic mulch beds in the field. The candidate crops must: 1) be very vigorous to choke out weeds; 2) be short in height to avoid competing with crops and not necessitate much mowing but must tolerate mowing with machinery to keep under control if necessary; 3) cover all the ground area, suppress and smother nutgrass; 4) be heat tolerant and not die during summer months; and 5) fix nitrogen to provide natural nitrogen fertility. Dutch White, Crimson Clover, Regal Ladino, Mt. Barker, Sweet White, Sweet Yellow, New Zealand, Nitro, Berseem, Overton, Rose, O’Connor, Kenland, Aliske, and Strawberry Salina were evaluated over three years and ‘Regal Ladino’ proved to be the best living mulch clover for weed control. When seeded in fall, ‘Regal Ladino” grows throughout the winter, grows vigorously through spring and summer, but dies by late August. ‘Regal Ladino’, however, leaves a thick mat of green manure on the soil’s surface in late summer after its decline. Another outstanding advantage of ‘Regal Ladino’ is its ability to suppress yellow nutsedge growth to a very high degree. Apparently this variety’s massive ground cover suppressed nutgrass emergence or possesses a high level of allelopathy that thwarted nutlet growth and development. Spring planting beds must be prepared in the fall and ‘Regal Ladino’ seed planted in October to allow germination and growth through winter for crop planting in March the following year. Spring planted Regal Ladino, however, is not recommended because warm climates apparently prevent seed germination.

Medicinal plants and commercial potential - Work was started in 1998 on cultural practices by many faculty at CREC on Echinacea purpurea and pallida, St. John’s Wort, valerian, and feverfew. We quickly found that St. John’s Wort and valerian were not climately-suited for production in coastal SC because of great susceptibility to Southern Blight. With all medicinals, the seed from available commercial sources are very heterogeneous and this variability within seed lots is evident in wide differences in plant growth habit, flowering and flower and leaf anatomy, biomass production and medicinal marker compound content (the chemical desired by the Dietary Supplement Industry). We have completed numerous studies on fertility (organic and inorganic), plant population, planting dates, harvesting pressure, etc., yet we have realized that inferior germplasm would limit the successful commercial production of specifically feverfew and Echinacea. Many available sources of germplasm from seed companies and the National Germplasm Repository were evaluated for ecotolerance throughout the spring, summer and fall growing season. Thousands of individual plants were sampled to discover those individual plants that contain high marker compound as well as ecotolerance. We have identified a handful of feverfew and E. purpurea individuals that have entered a breeding program with the objective of breeding new varieties of medicinals highly suited for production in the humid SC coastal region. To our disappointment, however, chemical analyses have indicated that marker compounds within these “super” plants are ephemeral and dynamic throughout the growing season. Hence, verification of germplasm superiority is impossible at this point, because of this enigma. Recently, we have detected “chronological windows” where marker compounds spike and if reproducible, all cultivars increase in marker compounds and developing new cultivars is unnecessary. For production to be successful, harvest dates need to be programmed into the cultural practices to target these spike dates.

Long-term effect of cold stress at transplanting on melon crops -  Exposure of plants of a tropical or subtropical nature, such as cucurbits, to low, chilling temperatures causes chilling injury in the form of stunted plant growth, wilting, necrotic lesions on leaves, and increased susceptibility to diseases and pathogens.  Growth reductions may be caused by several factors, including impaired photosynthesis, respiration, membrane integrity, and hormonal balance.  Melons transplanted very early in spring may be subjected to repeated chilling stress and the optimum air temperature for plant growth ranges from 20 to 320C, with 180C (minimum) and 350C (maximum).  Because one-half of the annual supply of the watermelons in the United States is consumed during the months of June and July, prices usually decline linearly during this time.  Therefore, the market demand dictates that growers supply watermelons early in the season in order to achieve higher prices and profits during the July 4th holiday.  Targeting late June and early July harvests in South Carolina, however,  requires field planting in early March before the last killing frost and optimum temperatures for plant growth.  Seedlings transplanted in the field may be exposed to temperatures cycling between chilling and optimal for weeks before the temperatures finally stabilize.  In some cases, frosts may destroy newly transplanted fields or stagnate early plant growth and establishment.  Therefore, it is hypothesized that exposure of watermelon seedlings to low temperatures may delay flowering, fruiting, and possibly reduce early and total yields and fruit quality. In order to insure early yields, muskmelon seedlings are transplanted in late winter or early spring before last frost date, making them very vulnerable to temperatures cycling between almost freezing and optimal temperatures. In our research study,  ‘Athena’, ‘Sugar Bowl’, ‘Eclipse’ muskmelon, and ‘Tesoro Dulce’ honeydew transplants were subjected to 2 ± 1oC in a walk-in cooler and then to 29 ± 5oC in a greenhouse before field planting to simulate temperature alternations that may occur after field transplanting.  In 1998, transplants were exposed to 20oC from 9 hours to 54 hours, and from 9 to 81 hours in 1999.  ‘Athena’ and ‘Sugar Bowl’ yielded less early melons in both years, whereas ‘Eclipse’ and ‘Tesoro Dulce’ early yields were only reduced in 1999.  Total yields of ‘Athena’ decreased linearly in both years with 10% yield reduction occurring with 12 to 21 cold stress hours.  Total yields of ‘Sugar Bowl’ decreased linearly in both years with 11 to 18 hours of cold stress causing 10% yield reduction in 1998 and 1999, respectively.  Although there was no significant relationship at the P=0.05 between cold stress and the yield of ‘Eclipse’ and ‘Tesoro Dulce’, their yields also decreased by as much as 42 and 41% with 81 hours of cold stress, respectively. Therefore, early planting before last frosts of all these muskmelon and honeydew cultivars should be done with caution since yield reductions are highly probable.

In the case of watermelon, similar research was conducted.  ‘Carnival’ watermelon transplants were exposed to cyclic cold temperature stress at 2 ± 1oC in a walk-in cooler and then to 29 ± 5oC in a greenhouse immediately before field planting to simulate temperature alternations that may occur after field transplanting.  Cold-stressed transplants were field planted after all risk of ambient cold stress passed.  In 1997, transplants were exposed to 2oC from 3 hours to 81 hours.  In 1998, exposure to 2oC ranged from 9 to 81 hours.   In 1997, cold stress decreased seedling shoot fresh weight, root fresh and dry weights, leaf area, chlorophyll and carbohydrate contents but did not affect shoot dry weight or seedling height.  In 1998, all seedling growth characteristics decreased in response to longer cold stress treatments.  The plants cold stressed for up to 81 hours continued to transpire more even one week after transplanting.  In both years, vining, flowering, and fruit set were delayed significantly with increasing hours of cold stress. Although early yields were unaffected, total yields decreased linearly in both years with increasing hours of cold with 38 to 40 hours of cold stress reducing yield 10% in both years.  Therefore, ‘Carnival’ watermelon variety should not be planted very early in the season if cold stress is expected.

 

Muskmelon as a new crop - Before 1978, muskmelons were largely seasonal items that appeared in local markets for a few months and then disappeared as late-summer and fall crops were harvested. Today, imports during the winter and early spring help satisfy consumer demand for year-round supplies of melons. U.S. muskmelon per capita use has increased since 1992 from about 8.8 to 11 lbs by 2005. Although California, Texas, and Arizona are major suppliers of muskmelon and honeydew melons, areas such as South Carolina, could supply more of the eastern markets. Current commercial recommendations for melons in coastal SC suggest that the earliest and latest recommended planting dates are Mar 15 and May 15th, respectively.  To establish an early market, many growers transplant much earlier than recommended, thus facing the risk of chilling injury to establishing plants. Extending the season would also be desirable in order to maintain some degree of dominance in the market but late plantings are difficult because of adverse summer weather conditions and increased insect and disease pressures.  To accomplish long-term production, growers need to make frequent plantings and select cultivars that perform well and are best-suited to unique growing conditions throughout the late winter, spring and summer growing seasons. A major problem, however, is the lack of knowledge of how different cultivars interact with unique growing season climatic conditions (temperature, daylength, rainfall, humidity, etc.) relative to yield, quality, and disease. Muskmelons are a high value specialty crop and long-term high quality production is desired to attract and gain some dominance in the market. The objectives of this study were to determine: 1) if transplanting melons earlier than recommended mid-Mar planting dates is effective in producing significantly earlier yields; and 2) the best planting dates from early Feb to Jul on the yield and quality for long term production of Athena, Eclipse and Sugar Bowl muskmelon cultivars, and the honeydew  cultivar--Tesoro Dulce. Melons were transplanted in Charleston SC in 1998, 1999 and  2000 on Feb 12 and 26, Mar 12 and 26, Apr 9 and 23, May 7 and 21, Jun 4 and 18, and Jul 2 and required 130, 113,105, 88, 79, 70, 64, 60, 60, 59, and 56 days from transplanting to reach mean melon harvest date, respectively. Stands were reduced 67%, 41% and 22% in the Feb 12 and 25, and Mar 12 planting dates, respectively, but < 15% in all other planting dates. Field planting before the recommended commercial mid-Mar planting dates did not produce earlier melons. These results agree with the other work we completed where we simulated cold stress in coolers before field planting (see previous paragraph).  Plantings made on Feb 12 and 26, Mar 12 and 26, and Apr 9, reached mean melon harvest about the same time on June 23, 19, 20, 22 and 27, respectively. Marketable numbers/plot (pooled over cultivar) were greatest in the Mar 12 and 26 planting dates, but 46% lower in the Feb 12 planting date compared to the Mar 12 planting date.  Sugar content was strongly related to planting date (pooled over cultivar) with greatest sugar content in the Feb 26 and Mar 12 planting dates but gradually decreasing with later planting dates.  The most productive cultivar in all 11 planting dates was Eclipse followed by Athena (in 8 of 11 planting dates); Tesoro Dulce was productive in 7 of 11 planting dates, but Sugar Bowl was productive only in 2 of 11 planting dates.

Risk of agricultural pollution - Nitrate fertilizer leaching and removal through phytoremediation - Nitrate fertilizers are used heavily in vegetable crop production have a high probability of leaching in our sandy soils into deep soil profiles and possibly polluting ground water and well water in regions in the Southeast US.  Areas in the Southeast, especially coastal areas, receive up to 52 inches of rain water per year which exacerbates fertilizer leaching. It has been reported by the Clemson University’s Department of Pesticide Regulation that many wells in the state have more than 10ppm nitrates, which has been deemed intolerable and may cause brain damage if ingested by infants. Beginning in 1998, we studied studying nitrate fertilizer soil dynamics in various vegetable production schemes using high fertility rates. In an attempt to remediate and remove leached nitrates, cover crops such as kenaf and sudan grass were grown as succession crops (phytoremediation) after heavily fertilized vegetable crops.  Eight foot deep soil samples were taken quarterly to monitor nitrate movement. We found that both kenaf and sudan grass removed nitrates that leached to a 4 foot depth, moved them to shallow areas near the soil surface and available for reuse by crops planted in rotation. These techniques verify an environmentally-friendly way to clean agricultural soils of excessive nitrates and avoid vegetable growers from being branded as “polluters”. Shallow wells were drilled in the field plots and sampled quarterly throughout the experimental period and we have found that high nitrates persisted in wells drilled in the field plots for at least 3 years. In March 2005, nitrate levels finally fell below the 10ppm acceptable level and this final cleansing of the soil required about 4 years.

Romaine lettuce as a new crop - Over the past 15 years, romaine lettuce (also known as Cos) has become one of the US=s most popular vegetables in terms of production, consumption, and exports.  US romaine per capita consumption has tripled since 1994, when it averaged 2.2 lbs, but by 2004, per capita use has reached a record 8.2 lbs. Although California, New Jersey, and Arizona are the dominant suppliers of romaine lettuce, areas such as South Carolina, could supply Southeast markets for fall, winter and spring production. To capture significant portions of the market, long-term production from fall to spring would be desirable. Romaine lettuce grows well in the Charleston SC area and >Parris Island Cos= cultivar was developed by Clemson University/USDA in 1955 to met local demands. In order to meet the changing market demands during the season, growers need to make frequent plantings and select cultivars that perform well and are best-suited to unique growing conditions throughout the fall, winter and spring growing seasons. A major problem, however, is the lack of knowledge of how different cultivars interact with unique growing season climatic conditions (temperature, daylength, rainfall, humidity, etc.)  relative to yield, quality, heat and cold, disease and bolting tolerances. In order for planting date and cultivar selections for commercial production to be successful in any locality, research needs to be done near potential commercial production sites. The objective of this study was to determine the best combination of planting dates and cultivars on yield and quality for long-term production of romaine lettuce. Green Forest (GF), Apache (AP), Darkland (DK), Green Tower (GT), Ideal Cos (IC) and Tall Guzmaine (TG) were successfully grown to harvest maturity on nineteen planting dates from Sept 1998 to Apr 2001. Lettuce planted in Sept and Apr, required as little as 47 and 49 days, respectively, to reach harvest (all cultivars harvested on the same day). Lettuce planted in Oct, Nov, Feb and Mar, required 64, 66, 75, and 67 days to reach harvest, respectively, but in the coldest planting dates of Dec and Jan, 90 and 98 days, respectively, were needed to reach maturity.  Of the eight planting dates evaluated, marketable numbers/plot (pooled over cultivars) were greatest in the Sept, followed by Apr (-8% decrease from Sept PD) > Mar (-13%) > Oct (-17%) > Nov (-21%) > Dec = Jan = Feb (~ -30%).  Heads weighed the most in Sept > Jan = Feb (-7% decrease from Sept PD) > Mar = Apr   (-14%) > Oct (-21%) > Dec (-25%) > Nov (-31%).  Cull yields (heads/plot) were greatest in Apr > Dec (-5% decrease from Apr) > Jan = Feb (-16%) > Nov (-27%) > Oct (-34%) > Mar (-44%) > Sept (-49%). Two out of three Nov planting dates were lost to freezing damage and this planting date should be avoided.  Significant bolting occurred primarily in the Sept and Oct planting dates with negligible bolting in the Nov, Dec and Jan planting dates, but bolting recurred again in the Feb, Mar and Apr planting dates. Marketable numbers/plot (pooled over all planting dates) were greatest for GF > GT (-7% decrease from GF) > AP (-8%) > IC (-9%) > DK (-11%) > TG (-21%). GF yielded the most marketable heads in 6 out of 8 planting dates. The best performing cultivar(s) by planting date were: Sept and Feb = GF and IC; Oct = TG; Nov = AP; Dec, Jan, Mar and Apr = GF.

Shrimp biosolids - Waste product from aquaculture, but a fertilizer for vegetables - Terrestrial shrimp lagoons are used to cultivate shrimp rather than fishing in the open ocean. As part of shrimp cultivation, the lagoons are drained into retention ponds after shrimp harvest and a rich sediment of shrimp fecal matter and decomposed shrimp food remain on the lagoon bottom. Normally these shrimp biosolids (SB) are bulldozed out of the ponds and placed in landfills as waste. SB soil tests indicate that the material is nutrient-rich and may be a useful fertilizer in vegetable production. Analysis of SB indicated a 6.8 pH, a cation exchange capacity of 8.00, 1996 ppm nitrates and many useful nutrients for plant growth, but also contained high Na and dissolved solids indicating that this material must be diluted in the soil solution or leached with water before use to prevent salinity problems.  SB has value as a fertility source, but SB used alone needs to be amended with commercial fertilizers to provide complete nutrition. The salt content of SB used in conjunction with inorganic fertilizers needs to be considered carefully, especially with moderately salt sensitive plants.  Before commercial use on other vegetable crops, individual trials need to be completed to avoid potential yield suppressions from excessive salts before SB is used on other vegetable crops. SB should be considered a valuable organic fertilizer and not a waste product. With proper flushing of salts, this material has a place in vegetable production or landscape use.

Sweetgrass - Domestication of a wild plant used in African-coiled basketry - Sweetgrass (Muhlenbergia filipes) is the main raw material in the construction of sweetgrass baskets by the descendants of enslaved Africans in the low country of the Southeast US. Natural sweetgrass usually grows behind the first dune along the ocean, but urbanization and beach front community construction, have destroyed many of the natural stands threatening the continuance of this ancient African-American folk art. Through research, trial and error, we have gained a fundamental understanding of how to grow sweetgrass in inland locations as a row crop.  Our grand experiment to grow vast acreage at Dill and McLeod Plantation was feasible, but maintenance of these plantings was not possible through a gross lack of volunteers from the basket making community. Sweetgrass plants in cultivation are short-lived perennials and within a three to five year period, many of the plants decline and need to be replaced. Especially critical, in the first year of planting in April when temperatures are warm, sweetgrass transplants need to be watered regularly to become established. In the first year of growth, fertilizer can occasionally be applied to enhance growth and vigorous root systems. In the years to follow, if the sweetgrass is grown for basketry, no fertilizer can be added since fertilizer causes the leaf blades to become weak and impossible to pull and totally useless in basketmaking. Sweetgrass quality improves with “benign neglect” and in those years after first planting, all that sweetgrass needs is weeding and fire ant control, but no fertilizer. If sweetgrass is grown strictly for ornamental value, it can be fertilized along with flowering plants in the landscape. Through the research and experience gained, I feel the best salvation to conquer supply problems should be an individual basis. Sweetgrass can be grown easily and successfully by individual basketmakers in their own backyards similar to a vegetable garden. A small 20 foot by 20 foot patch should sustain the yearly needs of an active basketmaker. A 50 foot x 50 foot sweetgrass garden was planted as a demonstration at CREC, viewed with approval by basketmakers and also harvested by basketmakers. The solution to sweetgrass shortage is solved; however, individuals have to grow their own plants on their own land, take ownership of those plants, not depend on native populations and wait for others to plant mass plantings of sweetgrass on lands of benevolent donors. There is a common belief that sweetgrass has to come from coastal beaches and dune areas, but with proper home cultivation, high quality sweetgrass is easily grown..

Education

1976   Norwich University - Biology, B.S.
1978   University of Vermont - Plant Science, M.S.
1982   Kansas State University - Horticulture, Ph.D.
 

Post Graduate Employment

1984 - 1986   Texas A & M University, Dept. of Horticulture - Assistant Professor
1982 - 1984   University of Minnesota, Dept. of Horticulture - Research Scientist
 

Professional Society Offices/Appointments

2003 - 2006  Board Member American Plasticulture Society

2001 - 2002  Chairman        Vegetable Crop Research Publication Award Committee   Amer. Soc. Hort. Sci.
2000 - 2001  Chairman        Herbs, Spices, Medicinal Plants Working Group               Amer. Soc. Hort. Sci.

1988 - 1989  Chairman        Seedling Establishment Working Group                           Amer. Soc. Hort. Sci.
1991 - 1992  Chairman        Seedling Establishment Working Group                           Amer. Soc. Hort. Sci.

Grants and Contracts

  • 2007-2008 Primary investigator in a grant from the Southern Region Small Fruit Consortium on forcing holiday strawberries with ChromatiNets.
  • 2005-2007 Primary investigator in a grant from a major medicinal plant processor to demonstrate the production of large scale commercial feverfew plantings.
  • 2005-2006 Co-investigator in a grant from the US Army Corps of Engineers to restore native plant populations on renourished beaches in Charleston, SC.
  • 2002 - 2004 Co-investigator in grants from the USDA Federal-State Marketing Improvement Program and USDA Specialty Grant Program to evaluate the production and development of nutraceuticals as alternative crops: Part II Refinement of quality standards for certification and branding.
  • 2002 - 2004 Primary investigator in SC Specialty Crop Grant Program evaluating cultural practices for medicinal plant production.
  • 2000 - 2002 Co-investigator in grants from the USDA Federal-State Marketing Improvement Program and USDA Specialty Grant Program to evaluate the production and development of nutraceuticals as alternative crops.
  • 2000 - 2002 Co-investigator in a grant from Clemson University's IPM Program to evaluate the management of pests on medicinal plants and influence of pest damage on marker compounds.
  • 2001 - 2003 Primary investigator in a grant from the Southern Region Small Fruit Consortium to evaluate off-season forcing of strawberries.
  • 1999 - 2002 Primary investigator in a grant from the National Crop Insurance to evaluate the effect of simulated hail damage to earliness, yield and quality of cauliflower.
  • 1999 - 2000 Primary investigator in a grant from Clemson University School Director to evaluate the potential of forcing strawberries for winter production with row covers.
  • 1998 Primary investigator in a grant from the Frost B-Gone Co. to determine the influence of Frost B-Gone in reducing the effect of cold temperature injury on tomatoes and watermelon.
  • 1998 - 2000 Primary investigator in grant from Clemson University's 2 x 4 funding to evaluate the status of potential fertilizer pollution from vegetable production and nitrate removal with cover crops using phytoremediation techniques.
  • 1998 - 2000 Co-investigator in a grant from Clemson University's 2 x 4 funding to evaluate the production potential for medicinal plants in SC.
  • 1995 - 1998 Co-investigator in a grant from the Seagrant Consortium to evaluate the potential of sludge from shrimp production lagoons as a fertilizer for vegetable crops.
  • 1986 - 1998 Co-investigator in a grant from USDA Science and Education to evaluate alternative cropping systems.
  • 1994 Primary investigator in a grant from the Trident Community Foundation for expansion of expansion of sweetgrass plantations at McLeod Plantation, James Island, SC.
  • 1994 Primary investigator in a grant from the Agricultural Society of South Carolina for expansion of sweetgrass plantations at McLeod Plantation, James Island, SC.
  • 1993 Primary investigator in a grant from the Seagrant Consortium to study rapid multiplication of sweetgrass plants.
  • 1992 Primary investigator in a grant from Miller Chemical and Fertilization Corp. to study effect of Cytokin on watermelon earliness, yield and quality.
  • 1992 Primary investigator in a grant from Microflo Co. to study the effect of plant growth regulators on tomato and cantaloupe.
  • 1991 Primary investigator in a grant from Miller Chemical and Fertilization Corp. to study the effect of Cytokin on watermelon earliness, yield and quality.
  • 1991 Primary investigator in a grant from PBT Co. to study the effect of Cytokin on watermelon earliness, yield and quality.
  • 1991 Primary investigator in a grant from Clemson Experiment Station, Special Provost Funds.
  • 1989 Primary investigator in a grant from the Agricultural Society of South Carolina to study the potential of Gerbera daisies for cut flower production.
  • 1987 Primary investigator in a grant from Asgrow Seed Company to study the relative maturity of broccoli varieties.
  • 1985 Primary investigator in a grant from the South Texas Melon Committee to study the carryover of fall-applied herbicides on spring muskmelon production.
  • 1985 Primary investigator in a grant from the Director of Research, Expanded Research Funds, Texas A&M University, to study the effect of herbivore feeding and salinity on growth of crucifers.
  • 1985 Primary investigator in a grant from Sierra Co. to study the potential for using Osmocote in the production of celery transplants.
  • 1984 Primary investigator in a grant to the South Texas Melon Committee to study the carryover of spring-applied herbicides in muskmelon production in fall.

Publications

·            Dufault, R. and B. Ward. 2008. Dynamic relationships between field temperatures and Romaine lettuce yield and quality. Scientia Horticulturae (In review).

·            Dufault, R., Hester, A. and B. Ward. 2008. Influence of organic and synthetic fertility on nitrate runoff and leaching, soil fertility and sweet corn yield and quality. Communications Soil Science Plant Analysis 39:(3+4) In press

·            Hassell, R., T. Phillips, R. Dufault and J. Ballington. 2006. Fall transplanting date affects strawberry cultivar performance. International Journal Fruit   Science 6(2):73-85.

·         Dufault, R., A. Korkmaz, B. Ward and R. Hassell. 2006. Planting date and cultivar affect melon quality and yield. HortScience 41(7):1-6.

·         Dufault, R., B. Ward and R. Hassell. 2006. Planting date and cultivar affect romaine lettuce yield and head quality. HortScience 41(3):640-645.

·         Rushing, J., R. Dufault, R. Hassell and B. Merle Shepard. 2005. Impact of GAP and GMP on feverfew plant marketability. HortScience 40(3):894.

·         Dufault, R. and B. Ward. 2005. Impact of cutting pressure on yield, quality, root carbohydrates and survival of spring-harvested and summer-forced asparagus in coastal South Carolina. HortScience 40(5): 1327-1332.

·         Dufault, R. 2005. Sweetgrass and its use in African-American folk art. Encyclopedia of Plant and Crop Sciences, Marcel Dekker, Inc., N.Y.

·         Rushing, J., R. J. Dufault and R. L. Hassell. 2004. Drying temperature and developmental stage at harvest influence the parthenolide content of feverfew leaves and stems. Acta Hort. 629:167-173.

·         Dufault, R. and B. Ward. 2004. Influence of defoliation timing and severity on cauliflower earliness, yield and quality.  Acta Hort. 618:421-426.

·      Hassell, R., R. Dufault and T. Phillips. 2004. Relationship among seed size, mother plant age and temperature on of Echinacea angustifolia, pallida and purpurea. Acta Hort. 629:239-243.

·      Hassell, R., R. Dufault, T. Phillips and T. Hale. 2004. Influence of temperature gradients on pale and purple coneflower, and valerian germination. HortTechnol 14(2):1-4.

·      Korkmaz, A. and R. Dufault. 2004. Differential cold stress duration and frequency treatments on muskmelon and field growth and yield. European J. Hort. Sci. 69:12-20.

·      Korkmaz, A. and R. Dufault. 2003. Short-term cyclic cold temperature stress on watermelon yield. HortScience 37(3):487-489.

·      Korkmaz, A. and R. Dufault. 2003. Influence of short-term cyclic cold temperature stress on muskmelon and honeydew yield. HortTechnol. 13(1):67-70.

·      Hassell, R., R. Dufault and T. Phillips. 2003. Low temperature response of su, se and sh2 sweet corn cultivars. HortTechnol. 13(1):136-141.

·      Dufault, R., J. Rushing, R. Hassell, M. Shepard and G. McCutcheon. 2002. Influence of fertility on the growth and marker compound of field-grown Echinacea species and feverfew. Scientia Horticulturae 1890:1-9.

·      Korkmaz, A. and R. Dufault. 2002. Short-term cyclic cold temperature stress on watermelon yield. HortScience 37(3):487-489.

·      Dufault, R. and A. Korkmaz. 2001. Potential of biosolids from shrimp aquaculture as a fertilizer for broccoli production.  J. Compost Science &  Utilization 9(2):107-114.

·      Korkmaz, A. and R. Dufault. 2001. Developmental consequences of cold temperature stresses at transplanting on seedling and field growth and yield. I. muskmelon. J. Amer. Soc. Hort. Sci. 126(4):404-409.

·      Korkmaz, A. and R. Dufault. 2001. Developmental consequences of cold temperature stresses at transplanting on seedling and field growth and yield. II. watermelon. J. Amer. Soc. Hort. Sci. 126(4):410-413.

·      Hassell, R., Dufault, R. and T. Phillips. 2001. Influence of temperature gradients on triploid and diploid watermelon seed germination. HortTechnol. 11(4):570-574.

·      Dufault, R. and A. Korkmaz. 2000. Potential of biosolids from shrimp aquaculture as a fertilizer for bell pepper production. J. Compost Science and Utilization. 8(4):310:319.

·      Dufault, R., D. Decoteau, J. Garrett, K. Batal, D, Granberry, J. Davis, G. Hoyt, and D. Sanders. 2000. Influence of cover crops and inorganic nitrogen fertilizers on tomato and bean crops grown in rotation. J. Vegetable Production. 6(2):13-25.

·      Dufault, R., Hassell, R., Rushing, J., Shepard, M., McCutcheon, G. and T. Keinath. 2000. Revival of herbalism and its roots in medicine. 1999. J. Agromedicine 7(2):21-29.

·      Dufault, R., Hassell, R., Rushing, J., Shepard, M., McCutcheon, G. and T. Keinath. 2000. Dilemma of regulating dietary supplements.  J. Agromedicine 7(2):69-80.

·      Keinath, A.P., J.W. Rushing and R.J. Dufault, 1999. First report of Southern Blight by Scerotium rolsii on St. John's Wort. Plant Disease Note 83(7):696.

·      Simmons, A., G. McCutcheon, B. Shepard, R. Dufault, R. Hassell, and J. Rushing. 1999. Bemisia argentifolii (Homoptera: Aleyrodidae) attacking species of medicinal herbal plants. Ann. Entomol. Soc. America 93(4):856-861.

·      Dufault, R. 1999. Mother stalk culture does not improve plant survival or yield of spring and summer-forced asparagus in SC. HortScience 34(2):225-228.

·      Dufault, R. 1998. Vegetable transplant nutrition. HortTechnol. 8(4):515-523.

·      Perry, K., Yihau, W., Sanders, D., Garrett, J., Decoteau, D., Nagata, R., Dufault, R., Batal, K., Granberry, D., and W. McLaurin. 1997. Heat units to predict tomato harvest in the southeast USA. Agricultural Forest Meteor. 84:249-254.

·      Dufault, R. 1997. Determination of heat unit requirements for broccoli harvest in coastal South Carolina. J. Amer. Soc. Hort. Sci. 122 (2):169-174.

·      Dufault, R. 1996. Dynamic relationships between field temperatures and broccoli head quality. J. Amer. Soc. Hort. Sci. 121(4):705-710.

·      Dufault, R. 1996. Forcing summer asparagus in South Carolina. Acta Hort. 415:175-182.

·      Dufault, R. 1996. Relationship between soil temperatures and spring asparagus spear emergence in coastal South Carolina. Acta Hort. 415:157-161.

·      Dufault, R. 1995. Harvest pressures affect yield of asparagus forced in summer in coastal South Carolina. J. Amer. Soc. Hort. Sci. 120(1):14-20.

·      Hodges, L., D. Sanders, K. Perry, K. Eskridge, K. Batal, D. Granberry, W. McLaurin, D. Decoteau, R. Dufault, J. Garrett and R. Nagata. 1995. Adaptability and reliability of yield for four pepper cultivars across three Southeastern states. HortScience 30(6):1205-1210.

·      Schultheis, J. and R. Dufault. 1994. Watermelon seedling growth, yield and quality following pretransplant nutritional conditioning. HortScience 29(11):1264-1268.

·      Dufault, R. and J. Schultheis. 1994. Bell pepper seedling growth, earliness, yield and quality following pretransplant nutritional conditioning. HortScience 29(9):999-1001.

·      Dufault, R. 1994. Impact of forcing summer asparagus in coastal South Carolina on yield, quality and recovery from harvest pressure. J. Amer. Soc. Hort. Sci. 119(3):396-402.

·      Dufault, R. 1994. Long-term consequences and significance of short-term pretransplant nutritional conditioning. HortTechnol. 4(1):41-42.

·      Perry, K., D. Sanders, D. Granberry, T. Garrett, D. Decoteau, R. Nagata, R. Dufault, K. Batal, and W. McLaurin. 1994. Determination of heat unit requirements for harvest of peppers with an evaluation of solar radiation and day length as model parameters. Ag. Forest Meteorology 65:197-205.

·      Dufault, R., D. Decoteau, T. Garrett, R. Nagata, K. Batal, W. McLaurin, D. Granberry, K. Perry, and D. Sanders. 1992. Scheduling collard planting dates regionally to lengthen the production period.  HortTechnol. 2(1):64-66.

·      Dufault, R., D. Decoteau, T. Garrett, R. Nagata, K. Batal, W. McLaurin, D. Granberry, K. Perry, and D. Sanders. 1991.  Determination of heat unit requirements for collard harvest in the Southeastern United States.  J. Amer. Soc. Hort. Sci. 114(6):899-903.

·      Melton, R. and R. Dufault.  1991. Tomato seedling growth, earliness, yield and quality following pretransplant nutritional conditioning and low temperatures. J. Amer. Soc. Hort. Sci. 116(3)