A monitoring program started in 2009 has generated valuable information about where downy mildew has been occurring on basil in the USA. Until 2019, each year a spreadsheet page was set up in Google Docs for anyone to log and view occurrence reports. A new website was launched in 2019 with a mapping program that mapped reports by county plus information about basil downy mildew. Gardeners have logged most reports over the years. Growers and extension staff have also reported.
After 14 years of reporting, not only is knowledge about basil downy mildew occurrence in the USA substantially better than it could have been without public help, reporters in the spreadsheet comments section provided valuable additional information including environmental conditions when disease appeared, its impact, and management practices tried.
This new disease, first observed in Florida in fall 2007, was reported in eight states in 2008. Since then through the monitoring program it has been reported in 44 states plus the District of Columbia. A total of 46, 64, 63, 77, 69, 268, 280, 213, 121, 108, 77, 79, 51, and 33 reports were logged in 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, and 2022 from 15, 23, 21, 28, 23, 36, 34, 37, 26, 34, 26, 23, 20, and 16 states, respectively. Total of 1549 reports. Large number of reports in 2014 was associated with cooler temperatures in the states where typical high summer temperatures might have limited downy mildew development in other years. Interestingly, some reports received since 2015 were from gardeners who had never seen downy mildew before; their basil had remained healthy all summer in previous years.
States where this disease has not yet been reported and/or confirmed are Arizona, Idaho, Nevada, South Dakota, Utah, and Wyoming. Unknowingly distributing contaminated seed is a plausible way that the pathogen was first introduced into the USA and how it has been spread long distances between geographically-separated areas. The pathogen produces spores easily dispersed by wind that enable it to move during the summer growing season through regions where basil is grown widely, including the eastern USA.
36 reports logged came from outside the USA: Canada (Quebec, Ontario, British Columbia), Belize, Mexico (Yucatan and Baja California), Grand Cayman, Puerto Rico, Jamaica, Costa Rico, Argentina, Ethiopia, Kenya, South Africa, Turkey, China, South Korea, and Australia, plus reports were received by e-mail from India and from a grower in Croatia with an outbreak on a resistant variety (Prospera) in 2022.
Please report when you see basil downy mildew!!! Thank you very much.
New map-based monitoring webpage.
Check previous occurrences in 2018, 2017, 2016, 2015, 2014, 2013, 2012, 2011, 2010 and 2009
Information about basil downy mildew and its management
