Updated June 2020. (Originally prepared for Vegetable MD Online.)
A monitoring program has been on-going since 2009 to map the occurrence and movement of basil downy mildew and to increase preparedness in growers and gardeners. The success of this activity depends on reports from anyone growing basil. Reports are also appreciated from outside the USA.
Instructions
To report your observations and see those of others, visit the Ag Pest Monitor: Basil and select the pull-down menu under ‘Reports’. If you are not yet on the Confirmed Reporter List, which includes plant pathologists and those who have submitted photographs to confirm a previous report, skip the ‘confirmed by’ section at the bottom. Your report will be posted on the map as ‘unconfirmed’. To obtain confirmation, you can contact your local diagnosis service for assistance and e-mail their diagnosis photographs of symptoms to mtm3@cornell.edu. Most important is close up image of the leaf underside showing the pathogen’s growth as this is diagnostic.
Under ‘Alert System’ you can sign up to receive notification when a report is logged about an occurrence nearby. Consult the monitoring site during the growing season to determine where downy mildew is developing in the USA.
Additional Information
A total of 1309 reports of basil downy mildew were logged from 44 states plus the District of Columbia from 2009 to 2018. More reports of downy mildew in 2014 than previous years was associated with affected plants for sale at garden centers in several states and cooler temperatures in the North Carolina to Maryland area where typical high summer temperatures might have limited downy mildew development in other years. 32 reports were from 18 locations outside the USA. Most reports were made by home gardeners, growers and extension specialists of sightings on outdoor plants. Affected plants were also seen in greenhouses. Many reports were confirmed by sending photographs to M. T. McGrath or because they came from reporters with expertise to identify downy mildew; some were not confirmed. Occurrence maps and additional information are available.
Success of the monitoring program depends on reports from anyone growing basil; therefore everyone is encouraged to enter observations. Information is needed about the planting and how the diagnosis was made. Reports are also valuable of locations where downy mildew is not found on basil. Monitoring will assist with determining whether seed is becoming a less important source, as expected with the pathogen’s ability to be seed-borne becoming well known, and whether movement of the pathogen via its wind-dispersed spores can be predicted based on knowledge of where downy mildew is occurring and forecasts of wind trajectories plus weather, as is done now for cucurbit downy mildew. Even before a forecasting system like that for cucurbit downy mildew can be developed, growers and gardeners alike will be able to look at reports in the spreadsheet to see if basil downy mildew has been observed near by.