Downy Mildew

Downy mildew is well known to growers of many different crops, but has not traditionally been a problem in herbs. Over the last several years, however, a new and aggressive downy mildew has been attacking field and greenhouse basil in North America and elsewhere. Basil downy mildew is caused by the fungus Peronospora belbahrii, which is a different species than the one affecting Ontario cucumber crops, or any other downy mildew known in the province, however its impacts on basil can be just as severe.

History of basil downy mildew
Prior to 2001, there had been only one report of downy mildew in basil, from Uganda in 1933. In 2001, basil downy mildew was reported in greenhouses in Switzerland, and over the next several years reports came from other European countries, as well as Israel, New Zealand, Argentina and Africa. It is not known what caused the change, but possibly a more aggressive strain of the pathogen evolved.

In North America, basil downy mildew was first reported in Florida in the fall of 2007. It is thought that the disease was spread to North America on contaminated seed. Downy mildew has since been reported in field and greenhouse basil in at least 10 US states. The disease was reported in Canada last year and in early June basil downy mildew was confirmed in a potted basil plant from a home garden in South Western Ontario. We have not seen any symptoms of the disease yet in basil plants that we are monitoring at the Simcoe Research station and have not had any reports from commercial fields in Ontario. However, in the US there have been numerous reports of downy mildew in greenhouse, commercial field and home garden basil in New York, Ohio, New Jersey, Delaware and other states since early June.







http://www.omafra.gov.on.ca/english/crops/hort/news/vegnews/2010/vg0810a3.htm