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Fighting Foliar Diseases Using Tools: Forecasters and Environmentally-Friendly Fungicides

Fighting Foliar Diseases Using Tools: Forecasters and Environmentally-Friendly Fungicides

M.K. Hausbeck, Michigan State University; M. Daughtrey, Cornell University, NY; L. Barnes, Texas A&M University

  1. INDUSTRY NEEDS ADDRESSED:

    Disease epidemics of Botrytis, powdery mildew (PM) and downy mildew (DM) can occur on floriculture crops without warning and vary in severity. Fungicides currently in use are at risk due to development of resistance by disease-causing organisms and pending regulatory action such as implementation of the Food Quality Protection Act. Further research on fungicides would not only identify effective products, but may provide new products with different modes of action that can be used in a management program aimed to delay the development of fungicide resistance in the pathogen. Increased knowledge regarding the influence of the environment on targeted pathogens and testing of disease forecasting systems currently available for agronomic crops may allow development of a system suitable for floriculture that would enable growers to time fungicide sprays and improve
    disease control.

  2. RESEARCH CONDUCTED, SPECIFIC RESULTS, AND BENEFITS TO THE INDUSTRY.

    Epidemiology and management of PM:

    A 2000-2001 fungicide trial in a Florida grower-cooperator field examining the efficacy of productsin controlling PM of gerbera daisies (see graph, right).Compass 50WG + Latron B-1956 completely prevented the development of PM. Applications of Insignia, Nova 40WP, Terraguard 50W, or Eagle 20 limited PM development to 1% of the plants infected. Compared to the other products included in this study, Strike 25WDG and Milsana + Latron B-1956 were least effective in limiting the number of plants infected and the number and size of colonies.

    A 2000-2001 fungicide trial at MSU testing the efficacy of products in controlling PM on poinsettia (see graph, left). With the exception of MT2001 (0.5 gal), all treatments limited disease compared to the untreated control. Applications of Systhane completely prevented PM development. Quinoxifen held disease to <1%. Products that limited disease to < 20% included Cinnamite + Cygnus, Cygnus, and Compass. At the end of the trial (61 days after the last spray), Quinoxifen treated plants had significantly less disease than all other
    fungicide treatments. Cygnus, Compass, and Cinnamite + Cygnus limited disease to <27%.

    A 1999 fungicide trial at Cornell was conducted examining the efficacy of fungicides for control of PM on poinsettia. With the exception of Heritage, all treatments suppressed PM compared to the untreated controls (see
    graph, right). On foliage, UBI 4206, BAS 500 00 F and Triact 70 treatments gave simlar control to that achieved with Terraguard 50W (8 oz/100 gal), an industry standard.

    Two fungicide trials during 2000 at Cornell were conducted examining the efficacy of products for control of PM on miniature rose (see graphs, below). Compass (0.5 and 1.0 oz/100 gal) and Compass (0.5 oz/100 gal) + Actigard (0.5 oz/100 gal) were more effective than Actigard alone in trial 1. All treatments in trial 2 suppressed disease, with the exception of PS 98 KD. Both Compass (2 oz/100 gal, 14-day) and Nutrol LC (1%, 7-day) gave significant PM suppression. The results of these trials indicated that there are several products both registered and under development that effectively manage PM of gerbera, poinsettia and miniature rose.



    Epidemiology and management of DM:

    Burkard spore trap and weather-monitoring equipment were placed at two sites at one commercial grower-cooperator in Florida to monitor the development of a naturally initiated DM epidemic on snapdragon during 1999-2000. Rainfall, relative humidity, temperature, leaf wetness, wind velocity and direction were measured and averages recorded hourly. Site 1 was monitored from 23 November through 5 May, and site 2 from 4 January through 5 May.When averaged over the season, airborne sporangia concentrations peaked daily from 6 to 8 AM.The amount of disease was highest on ‘Potomac Early Pink’ and ‘Rocket White,’ and lowest on ‘Potomac Apple,’ ‘Potomac Dark Orange’ and ‘Potomac Rose.’

    Knowledge of environmental parameters that favor disease development may provide a management tool for growers to utilize when applying fungicide sprays.Identifying resistant cultivars is a useful tool in making management decisions.

    Epidemiology and management of Botrytis:

    A fungicide trial conducted at MSU examined the efficacy of fungicides for control of Botrytisblight on geranium.Heritage and Decree significantly decreased blighted leaves (%) compared to the untreated inoculated control plants (see graph, right).All treatments except Medallion decreased sporulating leaves (%) compared to theinoculated control.

    Epidemiology and Management of Scab:

    A fungicide trial was conducted at Cornell to compare the effectiveness of materials for control of poinsettia scab. All products tested suppressed infection (see graph, right). Residue exceeded the commercially acceptable level (residue rating of 3.5) for both Spectro and Junction treatments. A second study examined the susceptibility of poinsettia cultivars to scab. Cultivars that showed the least symptoms were ‘Freedom Red,’ ‘Freedom White,’, Holly Point’ and ‘Winter Rose Dark Red.’ Cultivars that showed particular susceptibility included ‘Red Satin,’ ‘Marblestar’ and ‘Heirloom Red.’

  3. PROFESSIONAL/PUBLISHED INFORMATION.

    Byrne, J.M., M.K. Hausbeck. 2001. Downy mildew on snapdragons: environmental monitoring and cultivar evaluation, 2000. American Floral Endowment, Special Research Report #001 (in press).

    Byrne, J.M., M.K. Hausbeck, and B.D. Shaw. 2000. Factors affecting concentrations of airborne conidia of Oidium sp. among poinsettias in a greenhouse. Plant Disease 84:396-400.

    Chase, A.R. and M. Daughtrey. 2001. Control of poinsettia scab in 2001. Proceedings for the 17th Conference on Insect and Disease Management onOrnamentals, Society of American Florists, Orlando, FL, pp. 3-5.

    Daughtrey, M. and Tobiasz, M. 2001. Evaluation of fungicides for control of powdery mildew on poinsettia, 2000. Fungicide and Nematicide Tests (in press).

    Daughtrey, M. and Tobiasz, M. 2001. Abstr. Control of downy mildews on miniature rose and snapdragon. Phytopathology (in press).

    Daughtrey, M. and Tobiasz, M. 2000. Comparison of fungicides for control of poinsettia scab. Page 19 in 2000 Annual Report, L.I. Horticultural Research & Extension Center, Cornell University, Riverhead, NY.

    Daughtrey, M. and Tobiasz, M. 2000. Comparison of poinsettia cultivars’ susceptibility to scab. Pp. 19-20 in 2000 Annual Report, L.I. Horticultural Research & Extension Center, Cornell University Riverhead, NY.

    Daughtrey, M. and Tobiasz, M. 2000. Evaluati on of fungicides for control of powdery mildew on poinsettia, 1999. Fungicide and Nematicide Tests 55:559.

    Daughtrey, M., J.M Byrne, and M.K. Hausbeck. 2000. Management of a new powdery mildew on poinsettia, 2000. American Floral Endowment, Special Research Report #107 (in press).

    “Fungicide update,” presented by M. Hausbeck at the Michigan Greenhouse Growers Expo, Lansing, MI, 1999, 2000.

    Hausbeck, M.K. 2001. Early detection key tocontrolling downy mildew. GM Pro 21(4):72-3.

    Hausbeck, M.K. 2001. Managing the mildews: Powdery and downy mildews. Proceeding for the 17th Conference on Insect and Disease Management on Ornamentals, Society of American Florists, Orlando, FL, pp. 135-142.

    Hausbeck, M.K., W.R. Quackenbush, and S.D. Linderman. 2000. Evaluation of fungicides for the control of powdery mildew of miniature roses, 1999. Fungicide and Nematicide Tests 55:561-562.

    “New tools for Botrytis management,” and “New floriculture research,” presented by M. Hausbeck at the California Growers Meeting, San Jose, CA, 2000.

CONTINUED FUNDING REPORT

Why project should be continued: This project has provided alternative chemistries for managing Botrytis, PM and DM. Continuation of this research is likely to identify additional
alternatives.

Goals & Objectives: To test new fungicides including those classified as reduced risk products or naturally-derived fungicides along with biocontrol agents for their ability to control Botrytis, PM, and DM and determine their suitability for replacing currently used fungicides. Determine the environmental trigger necessary for diseases to develop and become epidemic.Develop a forecaster that would warn growers when environmental conditions are favorable for disease development so that a timely preventive fungicide applications could be made.

Impacts of Research: Identification of products as alternatives to currently used fungicides in managing Botrytis, PM, and DM should give growers more choices for disease management while delaying development of fungicide resistance in pathogens.Increased knowledge regarding the influence of the environment on targeted pathogens and testing of disease forecasting systems currently available for agronomic crops may allow development of a forecasting system for floriculture that will enable growers to time fungicide sprays and improve disease control.

Dissemination plan forresults: Research results will be presented at professional conferences and published in refereed and nonrefereed journals, magazines, and Fungicide and Nematicide Tests.

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