calling all gardeners: report basil downy mildew occurrences!

basil_dm8832x500CALLING ALL GARDENERS: When she set up the Google Doc seeking help monitoring outbreaks around the nation of Basil Downy Mildew, a devasting disease of the popular herb, plant pathologist Dr. Meg McGrath of Cornell thought it would be Extension people who filed outbreak reports. In fact, it’s been gardeners for the most part who are lending their watchful eyes—and furthering Meg’s research in the process.

“Their reports have helped me a lot in my work to understand where this disease is occurring, and what conditions are most favorable,” she says. “But we scientists always want more information! I am especially interested to hear from gardeners in states where I have gotten few or no reports.”

So gardeners: Is your basil in trouble? The tipoff: The plants look pekid, the tops of its leaves marked with diffuse yellow (top photo, as infection begins), as if hungry for fertilizer, but then going brown. Turning them over reveals distinctive vein-bounded brown or fuzzy gray patches (starting in photo below). The decline continues; leaves drop.

basil_dm8828x500Plant pathologists including Meg, plants breeders and other experts like the ones in this story are part of the collaboration of scientists working to identify, understand and hopefully outsmart plant diseases like Basil Downy Mildew, in turn helping gardeners and farmers succeed. Now we can lend a hand—specifically with Basil Downy Mildew.

(Photos from Dr. Meg McGrath of Cornell.)

  1. amen kahwajy says:

    Had all my Genovese develop this last year.

    This year Ram @ Forrest Green Farm in Louisa Va suggested we try Eudora as it might be more resistant.
    He says most growers he knows had a similar problem in Central Va in 2014.

  2. Michele Duncan says:

    Just had powdery mildew on a nano basil which was indoors and a regular basil which was out doors. This was the first time this has happened to me. I’m in Washington state
    and it has been unseasonably hot

  3. Diana Brownlie says:

    So that’s what it is!

    I was horrified to see my lush, heathy Genovese basil turning yellow, first the underneath leaves, and now almost overnight spreading to the tips. Weather has been very humid — I’m emptying the indoor humidifier every day, sometimes twice.

    After reading the article all the way through, I went out and cut down all the Genovese. The purple seems to be less affected, so I left it standing pro tem.

    To make my winter supply of pesto, I plan to buy basil from my CSA program (all organic). Just hope they haven’t been likewise blighted!

    Thanks for all your interesting and useful information.

    p.s.: (for your database)

    I garden in Syracuse, NY, at a higher location in the city which is usually 5 or more degrees warmer than the rest of the city. The garden is all organic, and has been so for the last eight years. Before me, there was nothing but unkempt grass, without “benefit” of lawn chemicals, and two fully-grown Norway maples, which I had cut down. The garden is all fenced in. (6″ high solid fence).

    1. margaret says:

      Fingers crossed you find a good source at a local farm, Diana. I say HURRY; what happened here last year was that suddenly everyone was hit, and there was nothing to be found from a local source when farmers pulled their crops.

  4. Jeri says:

    Mystery solved !!! THANK YOU
    Yep .. I’ve got it too.
    I couldn’t understand what was going on. I thought perhaps I had been too vigorous cutting it for the last big bunch of pesto I made for a gathering. Or that it had something to do with the more than usual rainfall making the debris from the adjacent anise hyssop falling on the basil leaves very soggy and sort of stuck.
    But it’s continued to languish, linger and deteriorate despite everything I do.
    FYI Location full sun, Columbia, MD 21044, organic for over 20 years.

  5. shiner says:

    I too lost my crop of Basil here in the mountains of NC. I reported it when I discovered what it was 2 weeks ago. Very sad and canonly hope next year I might make it through without Downy Mildew.

  6. Louise says:

    All of my Genevese basil are droopy and may in fact have the wilt. Last year all the plants failed but some Red Rubin rooted inside meant I had a little basil.

    This year I made garlic scape and chive pesto just to be sure to have pesto. The Red Rubin is doing a bit better but I also diversified to add a Pesto Perpetuo plant which is doing OK and my healthiest basil is a Fairytale Ajaka which is healthy and lush. It has darker green leaves and purple stems. I want to save seed from these two.

  7. Tracy says:

    My basil has escaped mildew, but some double impatiens is suffering this year, despite local nurses hopeful assurances.

  8. Rose says:

    Interesting that many comments specifically mention Genovese basil. I also lost all plants of this variety last year. This year I switched to other varieties such as the red Osmin, mini Pistou, and Thai Siam Queen. Despite the intensively hot and humid July here is Laurel, MD, no signs of mildew on any plants. Too bad I didn’t also plant Genovese for comparison.

    Wonder if the problem is with Genovese seeds infected with mildew from seed growers? Sort of like the multi year downy mildew issue with Impatiens (I. walleriana).

    1. Meg McGrath says:

      Infested seed can be a source of the pathogen, but the main problem with basil downy mildew is the pathogen’s wind-dispersed spores. A similar downy mildew affecting cucumber and other cucurbits is annually tracked jumping from southern FL to New England. Problem with impatiens downy mildew is that pathogen can survive in soil, in contrast with the other two. Spores have been blown to my basil every summer since 2008, so I now have some of my basil in pots in bins that I can bring in from the deck and put on the washer + dryer (that are conveniently right inside the door) overnight and on rainy days.

  9. Minnie says:

    Interesting to read this report and add to it. I figured our wet weather after a dry spell had brought on the mildew and wondered what to do about it. Wish I’d made pesto last week!

    1. margaret says:

      Hard to imagine cooking without it, and love having it in the garden to use as-needed. But lately that’s a tricky prospect, and doesn’t always work!

  10. Carolyn magnani says:

    2014 my neighbor had what I thought was a mildew but checked with our county extension which reported no reports in Iowa. The next week my basil also had the problem. Sometime later the extension said ISU had confirmed the mildew. We both disposed of our plants.
    2015 we both planted basil in new locations with better air flow. Last week my neighbor reported he again lost his basil while mine is still looking good.

  11. Beverly, zone 6, eastern PA says:

    I am growing ‘Eleonora’ Basil this year and lost none. About one dozen plants continue to look fine. We have had good, regular rainfall for June, July and August so far, plus a lot of heat and waves of humidity lasting several days each time. Today is forecast to be 95 degrees with humidity.

    Last year, 2014, I lost all 12 Genovese Basil plants, spaced all over the garden, got no pesto at all. Very sad! I thought it was spider mites because of the smutty looking leaf-backs. (not wearing glasses at the time). I threw out my saved seeds, bought new seeds and grew ‘Eleonora’ easily, starting indoors in April. I gave the plants better spacing for air flow in the garden beds just in case and religiously avoid overhead watering.

  12. AS Jones says:

    Interesting! I had no idea downy mildew was a “thing” for basil. I planted 7 types this year and the Siam Thai was the first to be felled. The entire crop went. Next to go was the Red Rubin. I feel idiotic saying this now but at the time it never occurred to me that it might spread, as I’d never grown the Red Rubin before, and I’ve never had basil get MILDEW before.

    I’ve got several other types doing just fine. You’d never know their cousins all died around them, either. The Genovese in particular is doing spectacularly. I’ve got about a gallon of pesto in the freezer right now.

    So what do we do? Keep an eye? Change conditions? Cover up?

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