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United States Department of Agriculture

Agricultural Research Service

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Research Project: Tracking and Managing Diseases of Floriculture Crops Caused by Oomycetes and Fungi

Location: Biological Integrated Pest Management Unit

2012 Annual Report


1a.Objectives (from AD-416):
Both oomycetes and fungi can be serious pathogens of floriculture crops, causing diseases that destroy the aesthetic quality and marketability of these economically important plants. Since each production business grows numerous plant species, there are many different plant-pathogen combinations that can result in harmful diseases. Introductions of new cultivars, shifts in weather patterns, changes in cultural practices, or even changes in control efforts against other greenhouse pests can suddenly favor pathogen development and lead to explosive disease outbreaks. New disease-causing agents, including familiar but genetically different pathogens, frequently are encountered on floriculture crops due to the introductions from exotic locations. The global movement of seeds, cuttings, and plants allows global spread of pathogens, despite our best quarantine and other regulatory efforts. This project will focus on some of the more common diseases affecting floriculture crops as well as some of the newer and more unusual diseases.

We intend to develop information to help growers reduce crop losses caused by various plant pathogenic fungi and oomycetes as well as key insect pests, including important vectors of plant pathogens. New methods and tools will be developed and effective integrated management practices will be identified. The objectives are to.
1)reduce crop losses caused by Pythium and Phytophthora species,.
2)better understand the threat of Fusarium wilt in floriculture crops.
3)develop more effective management strategies for fungi that commonly cause root rots, especially Thielaviopsis basicola and Rhizoctonia solani,.
4)develop effective management programs for rust diseases on roses and chrysanthemums, and.
5)improve the integration of root rot disease management practices with biologically-based IPM programs being developed for insect pests. The latest scientific methods will be employed in order to improve the success of IPM programs for floriculture crop production.


1b.Approach (from AD-416):
Project objectives will be addressed by testing disease management strategies—including sanitation methods and cultural practices as well as biopesticides and chemical fungicides—in greenhouse and field trials at Cornell University’s Long Island Horticultural Research and Extension Center. Research plots will be replicated and the data will be statistically analyzed. We also will collaborate closely with researchers at Oklahoma State University to improve our greenhouse sampling techniques for oomycete pathogens and to learn how to use molecular tools effectively to pinpoint the source of pathogen outbreaks within production pathways. This work will involve sampling from cooperating greenhouse operations and identifying isolates by morphological and molecular-based methods in the laboratory. Conducted in cooperation with USDA-ARS researchers at Ithaca, NY, laboratory assays and small-scale greenhouse tests will elucidate the nature of Bradysia fungus gnat/Pythium associations and the role of fungus gnats in root rot disease outbreaks and also assess compatibilities among fungicides used for control of root rot diseases and beneficial fungi (mycoinsecticides) used against insect pests.


3.Progress Report:

Four Long Island greenhouse businesses were intensively sampled in 2012 for members of the genera previously known as Pythium, which now include Pythium and Globisporangium. During the spring and summer bedding plant production season, samples were collected weekly from growing crops, pot-filling stations or from the ground outside the greenhouses. Pythium isolates were captured from 389 media and soil samples using baits of potato pieces, resulting in 74 isolates. These new isolates continued to show the population pattern evident in FY2011: the dominant species is Globisporangium irregulare sensu lato according to morphological identification, but we are finding that this group comprises extensive genetic diversity and will require a new taxonomic treatment once it is better understood.

The population structure of collected greenhouse isolates has been analyzed using ITS sequences and simple-sequence repeats (SSR) by collaborator C. Garzon at Oklahoma State University. Nine Globisporangium species and 5 Pythium species were identified. Four groups were found within the G. irregulare sensu lato isolates using principal component analysis of microsatellite data of a subset of 22 strains. The groups were nested within two distinct lineages: one containing just G. irregulare sensu stricto and one containing G. cryptoirregulare and G. cylindrosporum as well as some G. irregulare sensu lato isolates.

A fall 2011 trial evaluated the effectiveness of reduced-risk and traditional fungicides applied at a 14-day interval against brown rust caused by Puccinia chrysanthemi on 5 cultivars of chrysanthemum. Chrysanthemum Golden Helga appeared resistant, while Brunette Barbie, Hankie Yellow and Beth Violet showed higher susceptibility than Marilyn White. Azoxystrobin and pyraclostrobin plus boscalid treatments were very effective at protecting against rust in the trial, while propiconazole and mancozeb did not give significant benefit. For Thielaviopsis root rot studies, a rating system was developed to assess the relative susceptibility of calibrachoas cultivars to the disease. In Rhizoctonia canker management studies, tests of experimental and registered fungicides demonstrated that fludioxonil (Hurricane) and A17922A both were very effective at higher tested rates.

A manuscript reporting our findings that the fungus gnat Bradysia impatiens is attracted to and stimulated to oviposit by a wide array of living microorganisms (both in pure culture and in association with plant seedlings) was accepted for publication: Braun, S.E., Sanderson, J.P., Daughtrey, M.L., Wraight, S.P. Attraction and oviposition responses of the fungus gnat Bradysia impatiens to microbes and microbe-inoculated seedlings in laboratory bioassays. Entomologia Experimentalis et Applicata, in press. Our previously reported research found that these insects are not significant vectors of Pythium root rot pathogens, and these findings provide an alternative explanation for the commonly observed association between fungus gnats and Pythium-infected plants in the greenhouse.

Results of all plant pathology trials were reported at the Cornell University Long Island Horticultural Research and Extension Center Plant Science Day and in presentations at bedding plant schools and floriculture conference across New York. Methods and results of experiments are posted online at http://www.longislandhort.cornell.edu/


Last Modified: 8/1/2014
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