Tip rot, or restricted end rot, is a new sweetpotato (Ipomoea batatas) disease/disorder in Mississippi with unknown etiology. Since pathogen isolations have been inconsistent, a relationship of this disorder with stress is proposed. This disease/disorder is manifested as a restricted lesion at or close to the proximal end of the storage root and appears after 2 to 4 weeks in storage. In many cases, the lesion necrosis expands internally. On-farm and research station studies with preharvest foliar applications of ethephon were conducted in Mississippi to determine the potential association of tip rot with ethephon-induced stress. In addition, the effects of ethephon rate and interval between application and harvest on tip rot were investigated. After 1 to 2 months in storage, tip rot incidence was observed mostly in storage roots from ethephon-treated plants. The increase in tip rot incidence was well correlated with ethephon rate. These results suggest that preharvest applications of ethephon trigger a response that results in the tip rot disorder.
Ramón A. Arancibia, Jeffrey L. Main, and Christopher A. Clark
Travis C. Teuton, John C. Sorochan, Christopher L. Main, and Thomas C. Mueller
The transition zone is one of the hardest places to maintain high-quality turfgrasses, and the overall research objective was to determine best management practices to establish new turf cultivars in this zone. Hybrid bluegrasses (P. arachnifera Torr. × P. pratensis L.) have been bred for heat and drought tolerance and may offer a new alternative to other turfgrasses. The specific cultivars examined in this research were ‘Thermal Blue®’ and ‘Dura Blue®’. Experiments were conducted during 2003, 2004, and 2005 in Knoxville, TN. ‘Thermal Blue’ was seeded at 50, 100, 150, 200, and 250 kg·ha−1 of seed. ‘Thermal Blue's’ ideal seeding rate was between 100 and 150 kg·ha−1 of seed in 2003 and 50 kg·ha−1 in 2004. ‘Thermal Blue’ was also seeded in January, April, July, and September of each year with 100 kg·ha−1 of seed. All seeding dates took ≈11 months to become well established. However, July seeding produced poor turf quality (less than 6) and was the only seeding date deemed unacceptable. ‘Thermal Blue’ and ‘Dura Blue’ were fertilized with ammonium nitrate at 100, 200, and 300 kg N/ha/year and urea formaldehyde at 200 and 300 kg N/ha/year starting in March of each year. These treatments were maintained at 2-, 3.5-, and 5-cm mowing heights. ‘Thermal Blue’ had higher quality evaluations and produced more clippings than ‘Dura Blue’ throughout the year. Higher fertility regimens increased quality evaluations in April but decreased quality evaluations in October. Increasing the mowing height improved turf quality and decreased biomass production for both grasses. A proposed optimum method for establishment included seeding ‘Thermal Blue’ in April at 150 kg·ha−1 and fertilizing with 300 kg·ha−1 of nitrogen and them mowing at 5-cm height. ‘Thermal Blue’ and ‘Dura Blue’ are adapted for the transition zone, but summer heat stress may cause turf quality decrease in the fall.
Travis C. Teuton, John C. Sorochan, Christopher L. Main, Thomas J. Samples, John M. Parham, and Thomas C. Mueller
‘Dura Blue’ and ‘Thermal Blue’ hybrid bluegrass have been selected for heat and drought tolerance. These grasses offer alternatives to traditional Kentucky bluegrass and tall fescue in the transition zone. Experiments were conducted in two locations during 2003 and 2004 at the University of Tennessee in Knoxville, Tenn. Nitrogen (N) was applied at 50, 150, or 300 kg·ha−1 N per year to ‘Apollo’ Kentucky bluegrass, ‘Dura Blue’, and ‘Thermal Blue’ hybrid bluegrass, and ‘Dynasty’ and ‘Kentucky 31’ tall fescue. The main effects of turfgrass and N were significant for color and quality observations. However, their interactions were not significant; therefore, only the main effects are shown. Acceptable turfgrass color (>6) and quality (>6) was observed for all varieties in May, August, and November. All N regimens showed acceptable turfgrass color and quality. However, 150 kg·ha−1 N per year was required to achieve optimum color and quality. ‘Kentucky 31’ produced higher clipping dry weights when N was applied at 50 kg·ha−1 per year than the other varieties. Nitrogen applied at 150 and 300 kg·ha−1 per year on ‘Kentucky 31’ and ‘Thermal Blue’ produced higher clipping dry weights than the other varieties. ‘Dynasty’ and ‘Kentucky 31’ had similar brown patch incidences at each nitrogen level. Increases in brown patch incidence occurred as N levels decreased from 300 (21%) to 50 kg·ha−1 per year (31%) for ‘Dynasty’ and ‘Kentucky 31’. Dollar spot incidence occurred on all bluegrass varieties from 7% to 24%. However, dollar spot decreased with increased N fertility. All turfgrass species tested were acceptable for use in the transition zone.
Christopher A. Clark, Washington L. da Silva, Ramón A. Arancibia, Jeff L. Main, Jonathan R. Schultheis, Zvezdana Pesic van-Esbroeck, Chen Jiang, and Joy Smith
Two distinct syndromes have emerged in some production areas that have caused losses of sweetpotato (Ipomoea batatas) storage roots during postharvest storage: a complex of fungal rots (end rots) progressing from either end of storage roots and a necrotic reaction (internal necrosis) progressing internally from the proximal end of storage roots. This study was conducted in multiple environments to evaluate whether the use of preharvest ethephon application and storage with or without curing after harvest could be used to screen sweetpotato breeding lines for susceptibility/resistance to these two disorders. Treating vines with ethephon 2 weeks before harvest and placing harvested roots directly into storage at 60 °F without curing resulted in the greatest incidence of end rots in each state and there were significant differences in incidence among the sweetpotato genotypes evaluated. However, when ethephon was not used and roots were cured immediately after harvest, the incidence of end rots was low in all the genotypes evaluated except for one breeding line. Incidence and severity of internal necrosis were greatest when ethephon was applied preharvest and roots were cured immediately after harvest, but two cultivars, Hatteras and Covington, had significantly more internal necrosis than all others.