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United States Department of Agriculture

Agricultural Research Service

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Research Project: Employing New Tools to Detect and Limit Phytophthora Root Rot, Downy Mildew, and Other Key Pathogens of Floral Crops

Location: Biological Integrated Pest Management Unit

2013 Annual Report


1a.Objectives (from AD-416):
Greenhouse-grown floral crops are constantly threatened by a great variety of pathogenic microorganisms and arthropod pests. Growers need integrated management strategies incorporating cultural practices and a wide variety of effective pesticides to grow a quality crop at a reasonable price. Reduced risk and biological pesticides with novel/unique modes of action are particularly needed for rotation schemes designed to manage resistance and reduce inputs of hazardous chemicals into the environment.

The overall objective of this cooperative research project is to develop new technologies and strategies for more effective management of diseases and insect pests of greenhouse floriculture crops. Specific objectives are to:.
1)determine the susceptibility among coleus cultivars to downy mildew;.
2)determine the host range and virulence of Phytophthora species that may infect floral crops within the Asteraceae, Fabaceae, and Solanaceae families;.
3)characterize the efficacy of new active ingredients, including reduced-risk fungicides, biocontrol agents, or biopesticides against Botrytis cinerea, Thielaviopsis basicola, Phytophthora spp. (specifically to include P. nicotianae, P. cactorum, P. citricola, P. cryptogea, P. drechsleri, P. tropicalis, P. capsici), Pythium spp., Rhizoctonia solani, downy mildew pathogens, and powdery mildew pathogens; and.
4)improve the integration of foliar plant disease management practices with biologically-based IPM programs being developed for insect pests.


1b.Approach (from AD-416):
Project objectives will be accomplished through establishment of an interdisciplinary research team that will pursue project objectives within the framework of our existing plant pathology research programs. Research will be conducted through close interaction with diverse growers throughout the United States. Research on new active ingredients and commercial products (including reduced risk fungicides and biopesticides) for control of Botrytis, Phytophthora, Pythium, Rhizoctonia, Thielaviopsis, downy mildew and powdery mildew pathogens will focus on identification of the most effective materials and determination of application rates, application intervals, and other factors that provide for highest and most consistent and reliable efficacy. Efficacy tests will be conducted in replicated research plots using susceptible crops. In collaboration with USDA-ARS researchers at Ithaca, NY, laboratory assays and small-scale greenhouse tests will assess compatibilities among fungicides used for control of foliar plant diseases and beneficial fungi (mycoinsecticides) used for insect pest management.


3.Progress Report:

A 15-cultivar trial was established and initiated, but the downy mildew inoculum (an obligate parasite) was limited and the inoculation was not successful despite efforts to optimize incubation. In response to grower interest, 28 cultivars of impatiens were tested for susceptibility to downy mildew; all cultivars became infected. Evaluated several genera of plants within these families for susceptibility to Phytophthora spp. Osteospermum ecklonis ‘Flower Power White’ (Asteraceae), Calibrachoa x hybrida ‘Cabaret White’ (Solanaceae), and Lupinus polyphyllus ‘Russell Mix’ were inoculated with P. capsici, P. cryptogea, P. drechsleri, P. nicotianae, P. citricola, P. cactorum, and P. tropicalis. P. capsici, P. cryptogea and P. tropicalis were statistically more pathogenic on the host plants included in this study than the other pathogens tested. P. capsici infection was rated as 2.0, 4.3 and 3.0 (1=healthy, 5=dead) on Osteospermum, Calibrachoa and Lupinus, respectively, a first report on these crops. The other four pathogen species included in these studies resulted in plants that were similar to the uninoculated control plants for the three crops. For each host that is susceptible to a particular Phytophthora sp., determine susceptibility among cultivars of the host. Six cultivars of Osteospermum (Asteraceae) were evaluated for susceptibility to P. drechsleri. A sampling of diseased crops with root rot in Michigan greenhouses included 32 cultivars in the following series: geranium Pinto, Pinto Premium, Orbit, Zonal; poinsettia Sonora, Freedom, Jubilee, Angelika, Monet; snapdragon Aromas and Liberty Classic. Phytophthora spp. were observed only on some of the poinsettia cultivars. Infected Calibrachoa showed necrotic crown lesions that progressed to the stems, asymmetric foliar wilting, roots brown and decayed and plant death. Osteospermum showed chlorosis then necrosis of lower leaves, stunting, wilting of all foliage and stem, and plant death. Lupinus showed chlorotic/necrotic foliage, stunting, wilted foliage and stems, roots ranged from brown and decayed to only slightly rotted, and occasional plant death. Characterized the efficacy of new active ingredients, including reduced-risk fungicides, biocontrol agents, and biopesticides against Botrytis cinerea, Phytophthora spp. (specifically to include P. cactorum, P. capsici, P. citricola, P. cryptogea, P. drechsleri, P. nicotianae, P. tropicalis), Pythium spp., Rhizoctonia solani, Thielaviopsis basicola, downy mildew and powdery mildew pathogens. Twelve efficacy trials tested 23 products (5 biopesticides, 5 reduced risk fungicides, 2 experimentals, 11 industry standards and other chemistries). Trials included downy mildew-impatiens (4 trials), powdery mildew-aster, Phytophthora-poinsettia, Pythium-geranium, and fungicide phytotoxicity trials (3 impatiens, 2 pansy and 1 each begonia, geranium, marigold, zinnia). In the initial screening and characterization tests, products will be tested using one susceptible crop per pathogen. Dosages (5 trials), application intervals (5 trials) and drenches vs. foliar sprays (4 trials) were tested. Impatiens downy mildew trials tested fungicide efficacy at 22, 35 and 80 days after the final treatment. Promising products from the initial trials will be included in additional replicated research plots using additional susceptible crops. New crops included powdery mildew-aster, and phytotoxicity trials on begonia and marigold. MILESTONE A2, B4/C4. Research advances will be disseminated to agricultural extension scientists and commercial growers/recommendations for effective use of novel control agents will be formulated and made available to product manufacturers, growers, and agricultural researchers. Eleven articles (6 refereed scientific, 1 extension, 3 proceedings) have been published and 9 presentations made at 4 regional and 2 at Michigan and 2 at Ohio growers meetings. The extension article about impatiens downy mildew posted 5/7/13 generated a lot of interest and has received 2,323 unique pageviews.


Last Modified: 10/30/2014
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