Fifty-six field plantings of `Baccus', `Citation', `Packman', and `Southern Comet' broccoli were made in Charleston, S.C., at 2-week intervals from February to November from 1990 to 1992. The objective was to determine broccoli's response to growing season mean (GSM) temperatures for several important market quality characteristics, such as head shape, color, density, leafiness, and bead size. Regression analysis determined whether quality was more affected by GSM minimum (min) or maximum (max) temperature for each head quality characteristic. Head leafiness and density of `Baccus' were insensitive to GSM min (7.0 to 23.5 °C) and GSM max (17.5 to 32.5 °C) temperatures experienced during these years. `Baccus' head color was unacceptable at <20.3 °C GSM max and head shape was unacceptable at <19.8 and >26.8 °C GSM max. `Citation' head color and leafiness were unacceptable at >20.5 and >20.2 °C GSM max, respectively. Head density of `Citation' was unacceptable at <19.2 and >28.9 °C GSM max and head shape was unacceptable at <18.4 and >25.7 °C GSM max. Quality of `Packman' was unacceptable for head color at <21.0 and >27.3 °C GSM max, head leafiness at >32.0 °C GSM max, head density at <8.4 and >18.0 °C GSM min, and head shape at >22.0 °C GSM max. `Southern Comet' head quality was unacceptable for head color at <9.2 and >16.5 °C GSM min, head leafiness at >32.0 °C GSM max, head density at <8.9 and >16.2 °C GSM min, and head shape at <21.0 and >25.3 °C GSM max. GSM min or max temperatures did not affect bead size of any cultivar during any planting time studied.
Robert J. Dufault
The purpose of this study was to investigate the effect of different cutting pressures (CP) of 3,6,9, or 12 spears per plant on `UC 157 F1' asparagus yield harvested in spring or forced in July or August. Ten-week-old seedlings were field planted in March, 1987 and forced to emerge from 1989 to 1993 by mowing fern in separate replicated plots in July or August. Forcing treatments were not spring-harvested. Harvesting was terminated if 1) 30 harvests had occurred or 2) 80% of all plants reached cutting pressure treatment levels before 30 harvests occurred. Forced yields were compared to normal spring harvests. Normal emergence time is from January to March. CP treatments affected yield more than harvest time (HT) during the first three harvest years, but, thereafter, HT treatments affected yield more than CP. The most productive HT/CP treatment combinations varied by harvest year as follows: 1989—spring at 9 to 12 spears per plant, July at 12 spears per plant, and August at 9 spears per plant; 1990—forcing in July or August at 12 spears per plant; 1991—forcing in July at 9 to 12 spears per plant; 1992—forcing in July or August at 9 to 12 spears; and 1993—forcing in August at 9 to 12 spears per plant. Total cumulative yields over the 5 year period were highest with forcing in July at 12 spears per plant and August at 9 spears per plant. The productive lifespan of spring-harvested `UC 157 F1' was only three years because of greater stand loss compared to summer forcing.
Ahmet Korkmaz and Robert J. Dufault
Watermelon [Citrullus lanatus (Thunb) Matsum. & Nakai.] seedlings may be repeatedly exposed to temperatures alternating between almost freezing and optimum soon after field transplanting. `Carnival', `Crimson Sweet', `Millionaire' and `Crimson Trio' watermelon transplants were exposed to cold temperature stress at 2 ± 1 °C in a walk-in cooler and then to 29 ± 5 °C 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 1998, transplants were exposed to 2 °C from 9 hours to 54 hours, and in 1999 from 9 to 81 hours. Early yields of all cultivars, except Carnival, significantly decreased with increasing hours of cold stress in both years. Total yields of `Carnival' decreased linearly in both years with a 10% yield reduction occurring from 14 to 15 hours of cold stress. `Crimson Sweet' yields were reduced in 1999 only, with 16 hours of cold stress reducing yield 10%.
Robert J. Dufault and Brian Ward
Excessive cutting pressure (CP) early in the lifespan of an asparagus (Asparagus officinalis L.) plantation may weaken and reduce yields and quality. The objective of this research was to determine how increasing CP affects yield, quality, and survival of spring-harvested and summer-forced asparagus. `Jersey Gem' asparagus was harvested for 4 years (1999–2002) in spring or summer-forced on 1 Aug. using the following CP (weeks/year from 1st to 4th years, respectively): 2, 3, 4, 6 (low), 3, 4, 5, 7 (medium), and 4, 5, 8, 10 (high). In all harvest years, as CP increased, marketable number and weight increased. Yield in spring harvest seasons significantly increased with each increase in CP. In summer, yield significantly increased only when high CP was used with equivalent yields at low and medium CP. With summer forcing, there were 48% and 55% fewer large spears at medium and high CP, respectively, compared to the same CP used during spring harvest seasons. Stands tended to decrease with CP from 1997 to 2003, but these differences were not significant and not severe enough to kill the plants. Yearly root fructose concentrations (RFC) with all CP increased yearly from 1999 to 2001 and plateaued from 2002 to 2003. From 1999 to 2002, RFC increased 53%, 27%, 13%, and 13% in unharvested control, low, medium, and high CP, respectively, indicating that with a greater CP, RFC decreased. RFC in summer-forced asparagus was significantly less than spring-harvested in 83% of all sample months. RFC in spring-harvested asparagus was similar to unharvested asparagus in February, March, April, November, and December; however, in all other sample months, spring-harvested RFC was significantly lower than unharvested control plants. The highest CP scheme is appropriate for spring-harvested asparagus based on greatest marketable yields and acceptable cull losses. For summer-forced asparagus, the lowest CP scheme is more appropriate based on acceptable marketable yields and to avoid undue plant stress verified by unacceptably large cull losses mostly attributed to spindly spear size and lower RFC.
Ahmet Korkmaz and Robert J. Dufault
Muskmelon (Cucumis melo) seedlings are transplanted in late winter or early spring before last frost date to ensure early yields; however, this makes them very vulnerable to temperatures cycling between almost freezing and optimal temperatures. To simulate temperature alternations that may occur after field transplanting, `Athena', `Sugar Bowl', `Eclipse' muskmelon, and `Tesorro Dulce' honeydew (C. melo) transplants were subjected to 2 ± 1 °C (35.6 ± 1.8 °F) in a walk-in cooler and then to 29 ± 5 °C (84.2 ± 9.0 °F) in a greenhouse before field planting. In 1998, transplants were exposed to 2 °C for 9 to 54 hours, and for 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 hours of cold stress. 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. Therefore, early planting before last frosts of all these muskmelon and honeydew cultivars should be done with caution since reductions in early yields are highly probable.
Robert J. Dufault and Mark Farnham
The objectives of this study were 1) to identify high-quality broccoli cultivars for field production in spring, summer, and fall seasons; and 2) to illustrate dynamic changes in head quality of promising cultivars for a particular growing season compared to head quality over all seasons evaluated. Twenty-four hybrid cultivars were grown in spring, summer, and fall growing seasons 1993 to 1995 included `Arcadia', `Baccus', `Bonanza', `Citation', `Claudia', `Early Dawn', `Embassy', `Emerald City', `Everest', `Exselsior', `Galaxy', `Galleon', `Goliath', `Green Comet', `Green Duke', `Leprechaun', `Packman', `Paragon', `Skiff', `Southern Comet', `Sprinter', `Sultan', `Symphony', and `Viking'. Head density, color, leafiness, and shape, bead size, and consumer use were documented. `Symphony' performed best in Spring 1993 and 1994, and only `Paragon' tolerated heat in Summer 1993 and 1994. Fall climate in coastal South Carolina is most conducive to high-quality production versus spring and summer seasons, with the following cultivars producing superior heads in both years: `Symphony', `Embassy', `Galleon', `Galaxy', `Sultan', and `Emerald City'. Quality defects for each cultivar in each inappropriate growing season will be illustrated.
Ahmet Korkmaz and Robert J. Dufault
Cantaloupe seedlings may be repeatedly exposed in the field soon after transplanting to temperatures alternating between almost freezing and optimal temperatures. In the first year of a 2-year study, `Athena' cantaloupe seedlings were exposed in walk-in coolers to temperatures cycling from 2 °C for 3, 6, and 9 hours daily to 25 °C for the rest of the 24-h period. Cold stress was repeated for 1, 3, 6, and 9 days before field planting. In the second year, transplants were exposed to 2 °C for 3, 6, and 9 hours for 3, 6, and 9 days before field transplanting. The objective of this study was to determine the long-term effect of early season cold temperature exposure on seedling growth, earliness, yield and quality by simulating the cold/warm alternations possible in the field in coolers. Cold-stressed transplants were planted in the field after all risk of ambient cold stress was negligible. In both years, exposure to cycling cold temperatures generally did not effect total productivity and fruit quality, although seedling growth characteristics were reduced in response to longer cold-stress treatments. In the second year, early yield was reduced by exposure to increasing hours of cold stress, but this was not significant in the first year. Therefore, cold temperature stresses occurring in the field at transplanting have negligible effect on yield potential of `Athena' cantaloupe.
Ahmet Korkmaz and Robert J. Dufault
Watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) seedlings transplanted before the last frost date may be exposed to temperatures alternating between freezing and optimal until field temperatures finally stabilize. Cold stress may ultimately reduce growth and yield. To simulate such temperature alternations that occur naturally after field transplanting, diploid `Carnival' watermelon seedlings were exposed immediately before field planting to cyclic cold temperature stress at 2 ± 1 °C then transferred to a greenhouse at 29 ± 5 °C. In 1997, transplants were exposed to 2 °C from 3 to 81 hours and in 1998, exposure ranged from 9 to 81 hours. Cold-stressed seedlings were field planted after all potential risk of cold stress in the field had passed. In 1997, cold stress decreased seedling shoot and root fresh and dry weights, leaf area, chlorophyll and carbohydrate contents but not seedling height. In 1998, all seedling growth variables decreased in response to longer durations of cold stress. Plants cold stressed for up to 81 hours transpired more for 1 week after transplanting than those exposed to shorter periods of cold stress. In both years, vining (date first runner touched the ground), flowering, and fruit set were delayed significantly as cold stress hours increased. 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. Data indicate that `Carnival' watermelon transplants exposed to cold stress soon after transplanting may suffer yield reductions.
Ahmet Korkmaz and Robert J. Dufault
For the earliest yields of spring melons, muskmelon [Cucumis melo L. (Reticulatus Group)] fields in the southeast United States may be transplanted in late winter before the last frost date. Seedlings may be exposed to cold temperatures cycling between almost freezing and optimal for weeks before warm weather predominates and such exposure may reduce later growth and yields. To test whether cold stress may reduce growth and yield, `Athena' muskmelon seedlings were subjected to cold stress at 2 ± 1 °C then transferred to a greenhouse at 29 ± 5 °C before field transplanting. In 1997, cold exposure durations were 3, 6, or 9 h and were repeated (frequency) for 1, 3, 6, or 9 d before transplanting. In 1998, duration levels were not changed but frequencies were 3, 6, or 9 d. In 1997, as cold stress increased, seedling shoot and root fresh and dry weights, height, leaf area, and leaf chlorophyll content decreased linearly, but shoot carbohydrates decreased curvilinearly and stabilized with ≈54 hours cold stress. In 1998, all seedling growth characteristics except leaf chlorophyll content decreased linearly as cold stress exposure increased. Leaf chlorophyll content decreased curvilinearly as cold stress increased to 36 h, but leveled off with more hours of cold stress. Even 1 week after transplanting, plants exposed to cold stress for up to 81 h continued to transpire more than control plants. In both years, vining (date first runner touched the ground) and male and female flowering were delayed significantly with increasing cold stress, but fruit set was affected only in 1998. Cold stress in 1998 delayed earliness with early fruit weight and number per plot decreasing as cold stress exposure increased. Total yields decreased linearly in both years as cold stress increased with 21 to 32 hours causing 10% yield reduction in 1997 and 1998, respectively. Results indicate a potential risk exists for yield reduction if `Athena' muskmelon is planted weeks before last frost dates.
Robert J. Dufault, S. Hopkins, and P. Sandifer
Our objectives were to determine 1) if shrimp sludge has any value as a soil amendment in broccoli production and 2) an appropriate rate of sludge for head production. Four levels of N–P–K per 15-L pot (in grams; 2.0 N–0.07 P–1.4 K; 4.0 N–0.14 P–2.8 K; or 6.0 N–0.21 P–4.2 K; and 0.0 N–P–K) were factorially combined and replicated 10 times with four volumes of shrimp sludge (0%, 10%, 20%, and 40% v/w in 15-L pots blended with 100%, 90%, 80%, and 60% Metro Mix 300, respectively). Four-week-old `Emerald City' broccoli transplants were planted into sludge + media–fertilizer mixtures on 12–14–95 and were grown to harvest maturity in a greenhouse. As sludge volume increased, the days to harvest, plant height, and root fresh weight: head fresh weight ratio decreased, but leaf number, fresh weight and area, head fresh weight, stem diameter, and shoot: root fresh weight ratio increased. As N–P–K rate increased, leaf number, area, and fresh weight, stem diameter, head fresh weight, and shoot: root fresh weight ratio increased, but root: head fresh weight ratio and plant height decreased. Using head fresh weight as the determinant, heaviest heads were optimized with 20% sludge and 4.0g N–0.14g P–2.8g K per 15-L pot. Sludge alone or N–P–K alone did not produce the heaviest broccoli heads as using combinations of sludge and N–P–K in a fertility program.