Page Banner

United States Department of Agriculture

Agricultural Research Service

Related Topics


Location: Emerging Pests and Pathogens Research

Project Number: 8062-22000-019-10-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 20, 2010
End Date: Sep 19, 2014

A. Phytophthora diseases have become a major problem in floral crops throughout the United States in recent years due to movement of infected plant material between greenhouse production facilities and the ability of the pathogen to become established in production facilities once introduced. Surveys of production facilities have identified P. nicotianae as the most commonly occurring Phytophthora sp. on a number of different crops but P. drechsleri, P. cryptogea and P. tropicalis also occur. A high percentage of isolates of P. nicotianae and P. drechsleri are resistant to the most commonly used fungicide, mefenoxam. Phytophthora tropicalis, a recently described species in Hawaii, is becoming more prevalent on many different floral crops across the entire U.S. Floral crop growers need disease management information and tools to reduce or eliminate losses due to Phytophthora diseases. Evaluation of new fungicide chemistry and biopesticides along with novel rotation schemes will be made in greenhouse trials. Cross-resistance of mefenoxam-insensitive isolates of P. nicotianae and P. drechsleri toward new fungicides chemistries will be tested. The persistence of mefenoxam-insensitive and sensitive isolates will be measured in simulated greenhouse productions systems including re-used irrigation water. Aggressiveness of P. tropicalis will be assessed in pathogenicity trials with the reported new hosts of this pathogen. Applications of fungicides for control of plant diseases are potentially disruptive of insect biocontrol programs that include fungus-based biopesticides (mycoinsecticides). An additional objective is to enhance integration of Phytophthora disease management practices with biologically-based IPM programs being developed for thrips, whiteflies, and other insect pests.

New management products in rotations with biopesticides to reduce environmental impact will be evaluated against the major species of Phytophthora attacking floral crops: P. nicotianae, P. drechsleri, P. cryptogea, and P. tropicalis on key crops for each pathogen. Greenhouse trials under drip irrigation and uniform disease pressure will allow comparison of different fungicide chemistries and rotation schemes. In vitro screening of new fungicides in different FRAC groups will be tested for cross-resistance with selected mefenoxam-insensitive isolates of P. nicotainae and P. drechsleri from floral crops in a microtiter plate assay. Putative insensitive isolates will be evaluated in greenhouse trials with appropriate floral crops to determine if fungicides in other FRAC groups are still effective in control. Simulated survival trials in our University greenhouse will test the ability of fungicide-sensitive and fungicide-insensitive isolates to survive on bench, floor, and tool surfaces between cropping cycles. P. tropicalis will be investigated in greenhouse pathogenicity trials for variation in aggressiveness toward the host of pathogen isolation compared to aggressiveness on other known floral crop hosts of this Phytophthora species. Laboratory assays and small-scale greenhouse tests conducted by collaborating USDA-ARS researchers in Ithaca, NY will assess compatibilities among fungicides used for Phytophthora control and beneficial fungi used for insect pest management. Project results will be distributed to growers and crop protection specialists through workshops, field days, and publications in print and electronic formats.

Last Modified: 05/27/2017
Footer Content Back to Top of Page