|WILLIAMS-WOODWARD, JEAN - University Of Georgia
Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2017
Publication Date: 7/6/2017
Citation: Williams-Woodward, J.L., Copes, W.E. 2017. Environmental factors impact Passalora sequoiae conidia counts from Leyland Cypress. Journal of Phytopathology. 165:538-546.
Interpretive Summary: Needle blight disease, caused by Passalora sequoiae, results in a progressive death of leaf tissue of Leyland cypress grown in tree nurseries, in the landscape, and on Christmas tree farms. Fungicide schedules can involve a high number of fungicide applications. To better understand fungicide timing, weekly spore count data and daily weather data was collected at Watkinsville, GA in 2001 and at Dearing, GA in 2002. Spores of P. sequoiae were trapped from June through December with peak numbers in September and October. Modeling showed cooler fall temperatures and a decreasing evaporative transpiration were associated with increased spore dispersal at both locations. Results validate the importance of regular fungicide applications in September and October and a need to further reduction from less frequent applications from June through August. This information will benefit cooperative extension specialists and businesses that produce Leyland cypress and research scientists working to maximize fungicide and control strategies.
Technical Abstract: Needle blight disease, caused by Passalora sequoiae, results in a progressive lost of leaf tissue on Leyland cypress (×Cupressocyparis leylandii) within container and field tree nurseries, in the landscape, and on Christmas tree farms. Fungicide schedules were developed in response to seasonal symptom progression and conidia dispersion without clarification of specific weather conditions influencing disease. Spore count data was collected approximately weekly, every 4 to 10 days, from June to December in 2001 in Watkinsville, GA and in 2002 in Dearing, GA. Conidia of P. sequoiae were trapped from June through December with peak numbers in September and October. Daily weather data summaries were obtained from a weather station at each location. A deterministic model was developed individually for both sites. Temperature and evaporative transpiration were the weather variables associated with Area Under the Spore Progress Curve (AUSPC) both years. Wind speed was an additional variable included in the model in 2001. AUSPC had a negative linear correlation with temperature in 2001 and 2002, with evapotranspiration and wind speed in 2001, and a negative quadratic correlation with evapotranspiration in 2002. The models show the importance of the seasonal fall shift to cool temperatures favoring increased dispersal of P. sequoiae conidia. The seasonal decrease in evapotranspiration (ET) indicates a more complex influence than temperature alone, but does not clearly identify how solar radiation, vapor pressure deficit, or relative humidity directly influence spore production or dispersal. The association between increased AUSPC and slower daily wind speed averages could be as simple as a greater spore load being carried at the 0.9 m height of the rotorod or represent an interaction with other weather variables, such as decreasing relative humidity.