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market-farming - Re: [Market-farming] Basil Downy Mildew

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  • From: Allan Balliett <aballiett AT frontiernet.net>
  • To: Market Farming <market-farming AT lists.ibiblio.org>
  • Subject: Re: [Market-farming] Basil Downy Mildew
  • Date: Fri, 7 Aug 2009 20:59:09 -0400

Thanks to all of you folks who drew my attention to this new disease. Fortunately, Cornell sort of let me off the hook by saying this is a new disease (2007) and is often mistaken for nutritional imbalance.

A hold up in official prescriptions for dealing with downy mildew on basil appears to be that there has not been a need for a basil fungicide so few fungicides are labeled for use on basil.

Frankly, I haven't had good response from using milk as a mildew spray. Have (all of) the rest of you?

I'm uncertified organic, so I'm a little open to non-OMRI solutions.

How about copper?

Neem?

I sure would like to get these plants back into production and keep them there. Basil has always been such a great CSA crop in this area. The members love it and, in the past, it seemed like we could harvest it every week until some time in September.... Not so this year!

-ALLAN IN WV

http://vegetablemdonline.ppath.cornell.edu/NewsArticles/BasilDowny.html

The basil downy mildew pathogen can be spread in contaminated seed, in infected basil leaves, and as wind-dispersed spores. Downy mildew also was observed recently on ornamental plants related to basil, in particular coleus and salvia. These plants all belong to the Lamiaceae family, which includes basils (Ocimum spp.), mints (Menta spp.), sages (Salvia spp.) and other aromatics. Recently the coleus and basil downy mildew pathogens were demonstrated to be genetically different; therefore, these ornamental plants are no longer considered potential alternative hosts. However, there are many ornamental basils that are also hosts to the pathogen affecting basil grown for use as an herb. Contaminated seed is most likely the way that the basil downy mildew pathogen has been able to move between geographically-separated areas. Basil is also marketed internationally. The pathogen found in FL has been shown to be genetically the same as that in Switzerland (100% homology in their sequences). Spores of the basil downy mildew pathogen are capable of being dispersed long distances. Infected basil leaves produce an abundance of spores. Thus the pathogen can spread widely once introduced to an area. This could explain the widespread occurrence of basil downy mildew in the eastern USA in 2008.
Few fungicides are currently labeled for this new disease. There are two phosphorous acid fungicides, ProPhyt and K-Phite,that have downy mildew under herbs on the current label. These fungicides were effective in fungicide efficacy experiments with applications started before or after initial symptoms were found. Actinovate AG is an OMRI-listed fungicide that is labeled for use on herbs and for suppressing foliar diseases including downy mildew. Other fungicides are expected to be labeled for this use in the future.




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