Skip to main content
ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research Unit » Research » Publications at this Location » Publication #339828
Title: Environmental Factors Impact Temporal Passalora sequoiae Conidia Counts from Leyland Cypress

Author
item WILLIAMS-WOODWARD, JEAN - University Of Georgia
item Copes, Warren

Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: 5/25/2017
Publication Date: 12/1/2017
Citation: Williams-Woodward, J.L., Copes, W.E. 2017. Environmental Factors Impact Temporal Passalora sequoiae Conidia Counts from Leyland Cypress. American Phytopathological Society. S5.110.

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 loss of leaf tissue on Leyland cypress (×Cupressocyparis leylandii) within container and field tree nurseries, in the landscape, and on Christmas tree farms. Fungicide schedules have been developed in response to seasonal symptom progression and conidia dispersion without clarification of the influence of weather conditions on disease. Conidia count data of P. sequoiae were collected approximately weekly from June to December in 2001 in Watkinsville, GA and in 2002 in Dearing, GA. Peak number of conidia were collected in September and October. Daily weather data summaries were obtained from a weather station at each location. Deterministic models were developed individually for summer (June 1 to September 30) and fall (October 1 to December 21) seasons. A 3-day lag of average daily temperature (T) had a positive quadratic relationship with conidia counts in summer. A 10-day lag of average daily T, vapor pressure deficit (VPd) and total solar radiation had a positive quadratic, a negative linear and positive linear relationship, respectively, with conidia counts in fall. The models show that the seasonal fall shift to cooler temperatures, along with a reduction in VPd and an increase in solar radiation, favor production and dispersal of P. sequoiae conidia.