Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2014
Publication Date: 3/20/2015
Citation: Grunwald, N.J., Press, C.M., Rolfe, K.J., Weiland, G.E., Davis, E.A. 2015. Efficacy of management tools for control of Pythium root rot of Douglas-fir seedlings, 2013. Plant Disease Management Reports. 9:OT004.
Interpretive Summary: Several commercially available products were evaluated for efficacy against three root-rotting plant pathogen species that cause disease on Douglas-Fir trees and can significantly impact tree seeding survival. The results of this experiment showed that a commercially available product called Subdue Maxx can significantly improve the survival of tree seedlings compared to seedlings that were not treated with anything. Additionally, several other products including an alternative, non-chemical product called BW240 also provided significant improval in seeding survival. These results are important for registration of pesticides for minor use crops.
Technical Abstract: This study was conducted as part of the IR-4 Ornamental Horticulture program to evaluate fungicides and biopesticides for management of root, crown and stem rots of ornamental plants caused by Pythium species. Pythium species used in this study were P. vipa (isolate 09), P. dissotocum (isolate 41-08) and P. irregulare (isolate 45-08). Isolates were cultured and added to soilless potting mix at a rate of 10% by volume. Experiments were conducted by planting Douglas-fir seeds in 4” plastic pots with 10 seeds per pot. Controls received only noninfested vermiculite. Pots were arranged in a randomized complete block design with 8 replications. All treatments (except BW240) consisted of fungicide drenches were applied as a 3.4 fl oz solution. Pathogen-only control treatments received equivalents of water. Pots were drenched with fungicide 3 days after inoculum was mixed with soilless media and 2 days prior to planting. Soil mix for the BW240 biopesticide treatments was mixed with the potting medium, left to air-dry for 2 days, then mixed with Pythium isolates, moistened, and left to sit for 2 days before seeding. Seeding was done on the same day, 20 Nov across all treatments. Plants were maintained in a greenhouse and seedling survival counts were taken. Certain treatments provided a significant seedling stand improvement over non-treated controls. Subdue Maxx was the best treatment resulting in significant disease control for all Pythium species. All other treatments had significant disease control as compared to nontreated plants but to a lesser extent than observed for Subdue. Some treatments appeared to be somewhat specific for certain Pythium isolates, for example Adorn performed similar to BW240, and Subdue Maxx in the test against P. vipa but performed more poorly against P. dissotocum and P. irregulare. No phytotoxicity was observed for any treatment.