A monitoring program started in 2009 has generated valuable information about where downy mildew has been occurring on basil in the USA. Each year a spreadsheet page was set up in Google Docs for anyone to log occurrence reports. Gardeners have logged most reports. Growers and extension staff have also reported.
After seven 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 42 states plus the District of Columbia. A total of 49, 63, 63, 75, 64, 284, and 281 reports were logged in 2009, 2010, 2011, 2012, 2013, 2014, and 2015 from 20, 26, 22, 26, 20, 36, and 34 states, respectively. 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 in 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 Alaska, Arizona, Idaho, Nevada, Oklahoma, 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.
Reports logged also came from Argentina, Australia, Mexico, Baja California, Grand Cayman, Costa Rico, Puerto Rico, Jamaica, Quebec, Ontario, British Columbia, South Africa, and South Korea.
Reports logged in 2015 have come from: AL, CA, CT, DC, FL, GA, IN, KS, KY, LA, MD, ME, MI, MN, MO, NC, NJ, NY, OH, PA, RI, TN, TX, VA, VT, and WA.