Illinois basil growers are advised to be on alert for downy mildew, a destructive new disease expected to plague basil this year. University of Illinois plant pathologists first discovered this disease late last August and predict it will be an annually-occurring disease.
"Illinois's conditions are favorable for it," said Mohammad Babadoost, U of I Extension plant pathologist. "I suspect basil downy mildew will be here for years to come based on the history of downy mildews in other crops. We are focused on doing all we can to control it."
Basil downy mildew is caused by Peronospora spp. Symptoms that growers should look for include leaf spot and foliar blight. The pathogen is spread by wind, seed and plant material. The cool, wet growing season of 2009 was an ideal environment to foster it, Babadoost said.
"This disease works fast — in just a matter of days it can take over an entire crop," Babadoost said. "When the basil leaf is damaged, growers can't sell it."
Currently, the best measure of protection is through chemical control, Babadoost said. Azoxystrobin (Quadris) and two phosphorous acid fungicides, ProPhyt and K-Phite, are labeled for use on basil, and studies show these products are effective against downy mildew. As well, Actinovate AG is an OMRI-listed fungicide that is labeled for use on herbs and for suppressing foliar diseases including downy mildew.
"These fungicides alone are not expected to provide season-long protection against downy mildew of basil," Babadoost said. "We are testing other fungicides on downy mildew in a commercial field in Momence to evaluate their efficacy for control of the disease."
In addition, he encourages growers to use uncontaminated seed and less susceptible cultivars. The commonly grown sweet basil is more susceptible than other basil species. He also points out that it's important to minimize leaf wetness and relative humidity.
This disease is new to North America. It was first reported in Africa in 1933. In 2001, it was found in Switzerland, and then it moved to Italy, Belgium and France. The first United States discovery occurred in south Florida in October 2007.
The total crop value of basil in Illinois is approximately $10 million per year. Babadoost estimates the gross value of basil at $10,000 to $20,000 per acre. An average growing season has five harvests.
"The basil industry in Illinois is relatively small in comparison to corn or soybeans," Babadoost said. "But it's a very valuable and important industry to our state. Controlling this disease is critical to its future."
Source : University of Illinois