Browsing by Author "Dr. Jonathan R. Schultheis, Committee Chair"

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    Characterization of Diploid Watermelon Pollenizers and Utilization for Optimal Triploid Watermelon Production and Effects of Halosulfuron Post and Post-directed on Watermelon
    (2007-03-06) Dittmar, Peter James; Dr. John W. Wilcut, Committee Member; Dr. David W. Monks, Committee Co-Chair; Dr. Jonathan R. Schultheis, Committee Chair
    Characterization experiment. The objective of this research was to compare several cultigens' vegetative characteristics, staminate and pistillate flower output over time, and exterior and interior fruit characteristics. In experiments conducted during 2005 and 2006, 15 pollenizer cultigens were evaluated. Based on shorter vines and internodes, pollenizers which produced a more compact plant were 'Companion', 'Sidekick', 'TP91', 'TPS92', and 'WC5108-1216'. Those cultigens with a standard vine length (longer vines and internodes) were 'Ace', 'Jenny', 'High Set 11', 'Mickylee', 'Mini Pool', 'Nun6017', 'Pinnacle', 'Summer Flavor 800' ('SF800'), 'Super Pollenizer 1' ('SP1'), and 'WH6818'. The greatest quantity of staminate flowers produced over the 5 week period was obtained with 'Sidekick' and 'SP1'; the lowest number with 'TP91' and 'TPS92'. The number of pistillate flowers produced over time followed a similar pattern according to each cultigen's production of staminate flowers. Based on fruit production and quality, pollenizers with consumption market potential include 'Mickylee', 'SF800', 'Mini Pool', 'Jenny', and 'Pinnacle'. Other pollenizers, such as 'SP1', have a white flesh and thin rind and should be used strictly as a pollenizer. Based on staminate flower production, certain cultigens may potentially be superior pollenizers and increase triploid fruit yields. Utilization experiment. Studies were conducted to maximize triploid watermelon fruit yields and quality by optimizing the choice and use of pollenizers. Treatments included 'Companion', 'Super Pollenizer 1' ('SP1'), 'Summer Flavor 800' ('SF800'), and 'Mickylee' as the only pollen source (#1-4); and the various combinations of 'Companion', 'SF800', and 'SP1' using two pollenizer cultivars as pollen sources (#5-7). Planting arrangement was compared; 'SF800' in a hill (#8) versus an inter-planted field arrangement. Time of pollenizer establishment was evaluated by establishing 'SP1'three weeks after planting (#9) with the establishment of 'SP1' at time of triploid plant transplanting. A triploid planting with no pollenizer (#10) was included to determine if pollen movement occurred outside of the treatment area. Pollen movement was minimal among plots. For individual pollenizer treatments, 'Companion', 'SP1', and 'Mickylee' produced similar total yields. The lowest yields were obtained with the 'SF800' treatment. 'Companion' produced more large fruit than the individual pollenizer treatments. Combining the pollenizers generally did not enhance triploid yields or quality. Inter-planting of pollenizers resulted in better yields than if hill planted. The late planting of 'SP1' resulted in a high percentage of severe hollow heart. The selection of pollenizer, planting arrangement, and time of pollenizer establishment are all important considerations to optimizing triploid yield and quality. Halosulfuron study. Studies were conducted to determine the influence of halosulfuron postemergence-direct and postemergence on growth and yield of 'Precious Petite' and 'Tri-X-313' triploid watermelon. Treatments included a nontreated check, 39 g ai/ha halosulfuron applied to 25% distal or proximal region, and over the top. Two additional treatments were applied to 'Precious Petite' only: 50% distal or proximal. Watermelon treated with halosulfuron had chlorosis, shortened internodes and increased stem splitting. Halosulfuron POST over the top of watermelon caused the greatest injury. Halosulfuron directed to 25 or 50% (distal or proximal) of the plant caused less injury than halosulfuron applied over the top. Stem splitting was greatest with proximal application. Internode shortening was greatest with distal applications. However, 'Tri-X-313' in the 25% distal treatment produced similar total and marketable fruit weight as the nontreated check at Clinton. Fruit number did not differ among treatments for either cultivar. In 'Precious Petite', differences were found in the marketable fruit weight at Kinston. Plants in the nontreated check and 25% distal end treatment had greater marketable fruit weight than the 50% proximal and over the top treatments. Limiting halosulfuron to no more than 25% of the watermelon plant will likely improve crop tolerance.
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    Effects of Grower Management Practices and Field Characteristics on Insect Damage to Sweetpotato (Ipomoea batatas (L. Lam.) Roots.
    (2005-10-31) Brill, Nancy; Dr. Kenneth A. Sorensen, Committee Member; Dr. George G. Kennedy, Committee Member; Dr. David W. Monks, Committee Member; Dr. Jonathan R. Schultheis, Committee Chair
    On-farm research studies were conducted with North Carolina sweetpotato growers to determine relationships between grower management practices and field characteristics with insect damage to sweetpotato roots. Injury by wireworm, Diabrotica spp., and Systena spp. (WDS) complex, sweetpotato flea beetle, white grubs, and whitefringed beetle was categorized by the incidence of roots injured by those species and the severity of injury on damaged roots. Severity was determined by measuring the length of sweetpotato flea beetle tunneling, the number of WDS holes and the diameter of WDS holes. The incidence of the overall insect damage, or injury by any species, was also obtained. Field locations for these projects served as replications. Questionnaire: In 2002 and 2003, sixteen sweetpotato growers provided twenty-six field locations where roots were sampled, graded, and assessed for insect damage. Growers responded to a questionnaire about these field locations. The cultural practices, tillage practices, and pesticides used by growers, as well as the weeds, soil drainage class, and rainfall amounts in those fields, were related to the insect damage on the sampled roots. Approximately 25% of North Carolina's planted sweetpotato acreage was represented by the project conducted in 2002 and 2003. Whitefringed beetle and white grubs caused the least amount of insect damage, 3.0% and 4.6%, respectively. Sweetpotato flea beetle damage averaged 18%, while the most damage, 29%, was caused by WDS. The cultural practices, pesticides used, and tillage practices varied considerably among the 26 field locations used for the questionnaire, indicating that, due to the high amount (average of 43%) of overall insect damage, current management practices used by sweetpotato growers are ineffective for controlling injury to sweetpotato roots by soil-borne insects. Growers who rotated sweetpotato crops with cotton, delayed the planting and harvest time, subsoiled their fields, and cultivated more than 3 times during the growing season had higher amounts of insect damaged roots from their fields. Overall insect damage on roots from fields in which chlorpyrifos was used was high, about 30%, even though that amount was less than the incidence of damaged roots from fields where chlorpyrifos was not applied (75%). If growers used herbicides they had less WDS damaged roots, although the use of the EPTC herbicide resulted in more grub and whitefringed beetle damage. Roots from poorly drained soils had more WDS damage than roots from well drained soils. Rainfall was positively correlated to the amount of sweetpotato flea beetle damaged roots. Time of planting and harvest study: In 2003 and 2004, six sweetpotato growers provided thirteen field locations where sweetpotatoes were planted early (on or before 28 May) and late (after 16 June). Roots were sampled in each of the fields at approximately 90, 105, and 120 days after each planting time, graded, and scored for insect damage. Yield was also obtained. An early planting and early harvest resulted in the least amount of sweetpotato flea beetle and grub damage, 16% and 1.7%, respectively, although grub damage was also low (1.7%) with a late planting and late harvest time. However, if growers planted late, sweetpotato flea beetle and overall insect damage was high (approximately 45 to 50%) regardless of when roots were harvested. The diameter of WDS holes was larger on roots harvested later in the growing season. The highest yield of number one grade roots, 21 t/ha, was obtained with a late harvest (120 DAP). These results suggest that growers will need to balance decisions between potential losses in yield, or more insect damaged roots, depending on the time that sweetpotatoes are planted and harvested.