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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #332871
Title: Timing fungicide application intervals based on airborne Erysiphe necator concentrations

Author
item THIESSEN, LINDSEY - Oregon State University
item Neill, Tara
item Mahaffee, Walter - Walt

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2017
Publication Date: 4/28/2017
Citation: Thiessen, L.D., Neill, T.M., Mahaffee, W.F. 2017. Timing fungicide application intervals based on airborne Erysiphe necator concentrations. Phytopathology. 101(7):1246-1252. doi: 10.1094/PDIS-12-16-1727-RE.

Interpretive Summary: Management of grape powdery mildew (Erysiphe necator) relies on numerous fungicide applications that follow a calendar or model-based application intervals. While effective in disease control, this approach assumes that E. necator inoculum is always present and results in unnecessary applications in the early spring. Our previous research demonstrated the 2.5r fungicide applications could be eliminated from a management program by waiting until inoculum was detected before starting the fungicide program each spring. There is potential that the quantitative molecular assays (qPCR) we developed to detect E. necator inoculum could be used throughout the growing season to quantify airborne inoculum concentration and adjust fungicide application intervals based on action thresholds. We also developed an inexpensive, field-ready quantitative loop mediated isothermal amplification (qLAMP) assay was developed to determine the airborne inoculum concentration of E. necator. Field implementation of both the qPCR and qLAMP techniques was assessed in 2013 and 2014 in several commercial and research vineyards in the Willamette Valley of Oregon from pre-bud break until the cessation of fungicide applications at véraison. The qLAMP assay quantification was similar to the qPCR assay in 2013 (P = 0.14), but significantly underrepresented spore levels compared to the qPCR assay in 2014 (P < 0.01). Only the qPCR was useful for timing fungicide application intervals. An average of 2.3 fewer fungicide applications in 2013 and 1.6 fewer fungicide applications in 2014 were used without significant differences in berry or leaf disease incidence between plots with adjusted fungicide application intervals or standard practice plots. This research continues to show that inoculum monitoring has benefits to reducing fungicide use for the management of grape powdery mildew.

Technical Abstract: Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases relies on numerous fungicide applications that follow a calendar or model-based application intervals, both of which assume that inoculum is always present. Quantitative molecular assays have been previously developed to initiate fungicide applications and may be used throughout the growing season to monitor airborne inoculum concentrations for adjusting fungicide application intervals. An inexpensive, field-ready quantitative loop mediated isothermal amplification (qLAMP) assay was developed to determine the airborne inoculum concentration of E. necator. Field implementation was assessed in 2013 and 2014 in several commercial and research vineyards in the Willamette Valley of Oregon from pre-bud break until the cessation of fungicide applications at véraison. The qLAMP assay quantification of biweekly collected samples was similar to the quantitative PCR (qPCR) assay in 2013 (P = 0.14), but significantly underrepresented spore levels compared to the qPCR assay in 2014 (P < 0.01). Due to a loss of sensitivity of the qLAMP assay, the qPCR was used to time fungicide application intervals. An average of 2.3 fewer fungicide applications in 2013 and 1.6 fewer fungicide applications in 2014 were used without significant differences in berry or leaf disease incidence between plots with adjusted fungicide application intervals or standard practice plots.