ACCESSION NO: 0190079 SUBFILE: CRIS
PROJ NO: LAB93535 AGENCY: CSREES LA.B
PROJ TYPE: HATCH PROJ STATUS: NEW
START: 01 OCT 2001 TERM: 30 SEP 2006 FY: 2004
INVESTIGATOR: Holcomb, G. E.
PERFORMING INSTITUTION:
PLANT PATHOLOGY & CROP PHYSIOLOGY
LOUISIANA STATE UNIVERSITY
BATON ROUGE, LOUISIANA 70893
Etiology, Biology and Management of Diseases of Ornamental Plants and Turfgrasses
NON-TECHNICAL SUMMARY: Disease problems cause serious losses of ornamental plants in nurseries, garden centers and landscapes. This project addresses diseases problems, their cause and control, on ornamental plants and turfgrasses.
OBJECTIVES: General objectives are (1) to identify and evaluate potentially important diseases to include pathogen identification (etiology) and disease biology regarding occurrence, development and spread, and (2) to evaluate disease management practices. Specific objectives are (1) evaluate cultivars for disease resistance/susceptibility, (2) determine the lowest effective rate of sodium bicarbonate that will control ball moss, (3) conduct pathogenicity tests with camellia pathogen Guignardia camelliae, (4) determine the cause of these diseases: Cassia virus disease, St. Augustinegrass leaf spot, leaf spot of Melampodium, blight of Catharanthus, leaf spot of crape myrtle and flower blight of oleander, and (5) evaluate systemically acquired immunity inducing agents for controlling leaf spot diseases.
APPROACH: Applied and basic research techniques including laboratory, greenhouse and field facilities will be used to address the objectives outlined.
PROGRESS: 2004/01 TO 2004/12
Seven ornamental plant species and 239 cultivars were evaluated for resistance/susceptibility to leaf spot, flower blight and rust diseases during 2004. Crape myrtle cultivar Miami was very susceptible to Cercospora leaf spot defoliation at two different sites while cultivars Acoma, Basham's Party Pink, Tuskegee and Tonto showed only minor defoliation at both sites. Rose cultivars Carefree Delight and Knock Out again showed good resistance to black spot, whereas cultivars Friendship, Tropicana, Arkansas and Bewitched were severely defoliated. Madagascar periwinkle cultivar Victory Blue was the most severely affected by Choanephora flower spot/blight and Titan Polka Dot was least affected. Alternaria leaf spot was most severe on Madagascar periwinkle cultivar Victory Lavender and least severe on cultivar Titan Polka Dot. Marigold cultivars Inca II Orange and Primrose were severely infected with Choanephora flower blight, but cultivars Aspen Flame and Aspen Orange showed only minor disease. For the second year in a row, daylily cultivars Judith and Leebea Orange Crush were severely infected with leaf rust, while Bitsy, Black Eyed Stella and Lullaby Baby were free of rust. In south Louisiana, daylily rust ratings should not be taken until November to obtain the most accurate results regarding cultivar susceptibility. It was found that several Earth Kind Rose cultivars were highly susceptibile to powdery mildew (Clotilde Soupert, Souvenir de St. Anne's, Georgetown Tea and Sarah Jones) and should not be grown in south Louisiana. Tests were conducted, at the request of Monrovia Nursery, that showed mimosa cultivar Bourbi (a recent introduction from Monrovia) to be susceptible to Fusarium wilt. Fresh weight of the green alga Cephaleuros virescens, grown in vitro, was greater when grown with sucrose than with dextrose and doubled when sucrose was increased from 10 to 40 g/L. Commercial pine bark leachates (30-day-old) significantly reduced mycelial growth of Ciborinia camelliae (camellia flower blight pathogen) at concentrations of 12.5 to 100% when added to the growth medium. After 82 days, these leachates were no longer effective in reducing mycelial growth except at 50% concentration and when filter sterilized (vs. steam sterilization).
IMPACT: 2004/01 TO 2004/12
Plant cultivar susceptibility information is of great value to production and retail nurseries, landscape businesses, homeowners, and extension and research personnel because the planting of resistant materials reduces production costs and losses. Information on daylily cultivar resistance to rust is currently of great interest since the disease has been in the United States for only about 4 years, but already occurs over the entire United States. Daylily growers are anxious for any information on cultivar susceptibility. Pathogenicity tests with the alga Cephaleuros have never been accomplished, because the alga has never been induced to sporulate in culture. Growth studies cited here are directed toward that goal. The negative effects of pine bark leachates on mycelial growth of the camellia flower blight fungus suggests that pine bark used as a mulch may reduce inoculum levels of this important pathogen.
PUBLICATIONS: 2004/01 TO 2004/12
1. Holcomb, G. E. 2004. First report of southern blight of Ruellia brittoniana caused by Sclerotium rolfsii in Louisiana. Plant Disease 88:770.
2. Holcomb, G. E., Owings, A. and Witcher, A. 2004. Reaction of Viola spp. cultivars to Botrytis flower spot/blight, 2003. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 19:O006. DOI: 10.1094/BC19. The American Phytopathological Society, St. Paul, MN.
3. Holcomb, G. E., Owings, A. and Witcher, A. 2004. Reaction of vinca Madagascar periwinkle) cultivars to web blight, 2003. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 19:O005. DOI: 10.1094/BC19. The American Phytopathological Society, St. Paul, MN.
4. Holcomb, G. E., Owings, A. and Witcher, A. 2004. Reaction of rainbow pink cultivars to Alternaria leaf spot, 2003. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 19:O003. DOI: 10.1094/BC19. The American Phytopathological Society, St. Paul, MN.
5. Holcomb, G. E., Owings, A. and Witcher, A. 2004. Reaction of daylily cultivars to natural rust infection, 2003. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 19:O002. DOI: 10.1094/BC19. The American Phytopathological Society, St. Paul, MN.
6. Holcomb, G. E., Raiford, T. and Witcher, A. 2004. Reaction of rose cultivars to black spot disease, 2003. Biological and Cultural Tests for Control of Plant Diseases (online.) Report 19:O004. DOI: 10.1094/BC19. The American Phytopathological Society, St. Paul, MN.
7. Holcomb, G. E. 2004. SAD and Palmetto. Louisiana Turfgrass Bulletin 4(2):1.
8. Owings, A., Holcomb, G. Witcher, A. and Bush, E. 2004. All America daylilies: Landscape performance and rust observations. Proc. Southern Nursery Assoc. Res. Conf. 49:414-417.
9. Owings, A., Holcomb, G., Bates, D. and Witcher, A. 2004. Fall and spring landscape performance of African marigold varieties. La. State Hort. Soc. J. 1:1-2.
10. Owings, A., Bush, E., Bates, D. and Holcomb, G. 2004. Landscape performance of miniature and dwarf crape myrtle cultivars. La. State Hort. Soc. J. 1:11-12.
PROJECT CONTACT:
Name: Holcomb, G. E.
Phone: 225-578-1386
Fax: 225-578-1415
E-mail: gholcomb@agcenter.lsu.edu