Downy Mildew on basil in greenhouse

[Julie Rubaud]

We are a certified organic greenhouse and were invaded by basil downy mildew this year for the first time. None of our basil was sale-able. We tried about 10 different varieties, a couple of different potting soils, and then started regular applications of Oxidate. Nothing worked, but we have no experience using Oxidate, and I don't think the twice a week spraying was enough. Any tips?

 

[Walter Gaipa]

Hi Mark,

Thanks for sharing your experiences. We had pretty good luck with keeping the greenhouse temperature above 70 degrees, as BDM thrives at 68. It seems to have helped control the symptons. Oxidate sprays had very little effect. We tried Regalia, with some sucess and will probably use more next year as we will only grow (or try to grow) organic basil. If we have problems we will switch back to conventional growing and spray with phoshites, which has the best control. But I have the same concern as you in regard to what we send out and what the customer ends up with weeks later. Kind of the same concern impatiens growers are having with downy mildew. But they can substitute other annuals. We don't have that option.

Do you have any seed sources you might recommend? I know California growers have had quite a problem as well.

Can you be more specific with your peroxide spray? What product and at what rate?

I agree cleanliness is the best approach.

Happy New Year!

Walter Gaipa

Marion Gardens, Organic Herbs
 
Mark Langan said:

Hi there everyone.

  Sorry I'm late to this discussion, I hope everyone is still following.  The holidays delayed in getting my profile setup are at fault.  First question, is this disease truly systemic, or semi-topical?  What I mean is, this, does this fungus grow it's mycelium into the stomata and the fruiting spores grow on the underside of the leaf(semi-topical and not an text book term), or does it transport throughout the plant to the growing points(systemic).  If this fungus does indeed grow "semi-topical" (grow with the first leaves and then sporulate up to the upper leaves?) then we have a chance to kill it in its' tracks (use any and all above suggestions).  If it is truly systemic and transports throughout the plant, then all we are doing is selling garbage, no matter what we spray to stop the spores, because the plant is thereafter truly infected.  For the customer to say " oh, I guess it was a bad year" will not allow us to stay in business.  If it is the former, then we have a opportunity to stop the spread.  I have been battling this for 3 years years , and am an Certified Organic grower.  Actinovate- do not waste money.  Oxidate / Preclude- no combination of sprays that I have tried have tried in the the field has worked with this (2% everyday X 3, followed by Actinovate + buttermilk- Cornell University), but for cleaning up an infected greenhouse has been great.  For greenhouse, remove all basils-then spray everything- under benches, floors, roof-everything!, spray peroxide 3-5 days in a row.  I have a Stihl backpack sprayer for the job.  For field, if you are in the south- you are probably (sorry) screwed.  In the north-pray for really hard winters.  Ann Chase was very little help on these issues.  What has been working for me,  has been peroxide for clean-up and then Suffoil-X  from BioWorks.  The Suffoil-X smothers the stomata and prevents sporulation. (I killed a great crop of Sage with the 4th spray, because I did not read the label) But does it prevent semi-topical sporulation on basil-if it does indeed grow this way?  It gave me a salable crop, but did the customers have a harvestable crop?

      Prevention, Please read.  I strongly believe and can confirm from Ann Chases article that the seed is infected (Organic seed from Johnnys will no longer be purchased).  But the question is once again, is it systemic or topical?  Robert Schuler said that DM is in the seed, Robert- help! got some research links to show this?  How is a fungus  "in the seed".  If this is true then my 3% peroxide soaks at 1 minute are worthless. P.S. No loss of seed germ., just a pain in the butt for sowing.  Lastly, ask for and know the seed source.  From India, Africa, Southern U.S. -in the words of a past famous N.Y. major " Foget about it".  Look for western U.S. or north as possible source.  Also ask these companies to certify that these fields were harvested from BDM free fields.  We as growers must collectively demand this.

   I hope I asked more questions than I gave solutions, to help us all keep this thread alive.

PEACE, Live and Long and Prosper.  Happy BDM free New Year!

Mark Langan, Mulberry Creek HerbFarm  419-433-6126

[Walter Gaipa]

Here is a really good link for info on BDM from Meg McGrath of the Cornell Research Lab in Riverhead NY.

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

 

[Mark Langan]

Hi Walter, Happy New Year

    I am now using Preclude (OMRI &  WSDA organic and does not have acetic acid like Oxidate), and have used it at 2% with no burn.  I will be trying 3% here soon.  For sterilizing the greenhouse, remove all basils-then spray everything- under benches, floors, roof-everything!, spray peroxide 3-5 days in a row.  I have a Stihl backpack sprayer for the job.  For my vegetative basil varieties(Aussie Sweetie/Lesbos, Cuban, Mini Purple, Pepper...., which are mildly infected, and definitly carriers. We took the smallest tip cutting, in 1% Preclude (not strong enough) rooted & grew those on.  I found those to be infected last week.  I took the smallest 1/2" tip cuttings again, this time at 2% Preclude (no burn, even after 60 second soak) and they are now rooted and looking good.  Greenhouse is getting sprayed with 2% daily for the next 3 additional days.

  Wish me luck

[Walter Gaipa]

Hi Mark,

Sounds like you have a plan of attack. I am guessing you are in Washington State? I know they are very strict with organic regulations. Any phosphites that they might allow?

I will try some of your ideas. There is no "silver bullet" here and alot of cultural and preventative measures work best.

Do you have any sources of clean seed?

Thanks and good luck!

Walter

[Meg McGrath]

I am a vegetable pathologist and an avid gardener who has been studying basil downy mildew and watching it develop in my garden every summer since 2008.  I have evaluated organic and conventional fungicides on field-grown plants.  And I’ve interacted with a lot of growers about BDM.  Here’s what I’ve learned:

- BDM is a tough disease to manage.

- Most important step is starting with clean seed. 

- Controlling humidity is also key to managing BDM in greenhouses.  Keep it below 90% at all times; below 85% is best.  Add more fans and lights.  Increase space between plants.

- Wind-dispersed spores are another important source of BDM.  Avoiding favorable conditions (high humidity) in a GH will be especially important when BDM is occurring on outdoor plants nearby.  The pathogen produces a lot of spores and disperses easily, thus becoming widespread each year.

- When BDM occurs, completely clean out the GH; don't try to keep plants that look to be free of the disease.

- BDM is very difficult to control chemically, even with non-organic fungicides.  One issue is the degree of control that is needed - a leaf with a little bit of BDM is as unmarketable as one that is covered.   I have tested many organic and conventional fungicides on field grown plants using a backpack sprayer.  In my last trial I used a boom with 3 nozzles (one directed at the top of the plant, one on each side of the plant) to improve coverage.  Only one of the conventional fungicides had significantly less BDM than the non treated plants – and these fungicides are mobile in leaves and have targeted activity for this type of pathogen.   The phosphorous acid fungicides (I tested K-Phite and ProPhyt) were not effective for me.  I'm looking for reduced incidence of affected leaves not just reduced severity as I feel that's what we need from a product for it to be commercially viable.  K-Phite has done well in other trials (NJ). 

- Sweet basil is much more susceptible than the spice and ornamental types.

 

I am studying occurrence of BDM and so would greatly appreciate hearing from those of you who have had it.  I want to understand how widely it occurs, and identify whether seed or wind-dispersed spores are the source of the pathogen for outbreaks.  A colleague working with me on this has developed a procedure for testing seed and he is studying genetic variation in the pathogen.  He would appreciate receiving affected plant material and seed suspected of being the source of the pathogen for an outbreak (our project has funding for this work, so no cost to growers)(contact me by email for shipping details).  There is a basil breeder working with us.  Hopefully he will be successful as resistant varieties would be an excellent tool!