Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2017
Publication Date: 8/4/2017
Citation: Press, C.M., Rolfe, K.J., Weiland, G.E., Grunwald, N.J. 2017. Efficacy of management tools for control of Phytophthora plurivora leaf spot of Rhododendron, 2014. Plant Disease Management Reports. 11:OT035.
Interpretive Summary: Various commercial products were tested for their potential to control leaf spot disease caused by the pathogen Phytophthora plurivora on Rhododendron plants including A21008A SC, SP2770WP, Promax, Micora SC, and Subdue Maxx EC. Products were applied to plants and plants were challenged with the leaf spot pathogen and incubated in a manner that was conducive to the spread of disease. Disease was assessed ten days after product application to determine whether or not they were effective in controlling leaf spot. Several of these products were effective at controlling leaf spot disease including Subdue Maxx, Micora, SP2770 (2.6 oz rate with one application and both rates with two applications) and A21008 (at 2.4oz rate and 1.2 oz rate after the second application).
Technical Abstract: This study was conducted as part of the IR-4 Ornamental Horticulture program to evaluate fungicides and biopesticides for management of leaf spot of Rhododendron caused by Phytophthora plurivora. The experiment was conducted by treating two-year old Rhododendron plants with fungicides on September 26, 2016 and again on October 1, 2016. Four single-plant replications were arranged in a randomized block design. Three days following each fungicide application, leaves were detached from each plant and inoculated with P. plurivora. Detached leaves were placed in containers to incubate and containers were placed in a growth chamber with a 14 hour photoperiod at 68°F. Every day, leaves were sprayed with distilled water to maintain humidity. Total lesion area was assessed 10 days after each leaf inoculation. Subdue Maxx, Micora, SP2770 (2.6lb rate with one application and both rates with two applications) and A21008 (2.4 oz rate and 1.2 oz rate after the second application) were the best treatments resulting in significant disease control as compared to the untreated inoculated controls. SP2770 (single foliar application) and A21008 at the lower rate did not confer any significant protection from P. plurivora compared to untreated inoculated controls. No phytotoxicity was observed for any treatment.