WANTED: Information on Occurrence of Basil Downy Mildew.


A scientist studying vegetable pathology at Cornell contacted GardenRant for help in gathering data about a new disease.  Please help out by spreading the word about the need for more info and how to report it.basil_dm_crop1x500

by Meg McGrath
I recently have received several reports of Basil Downy Mildew on plants bought or for sale at big chain garden centers.  Today I found in a store here.  I want gardeners to realize this is happening so they can avoid buying a diseased plant and also be looking and reporting so we know how widespread the issue is.  
The diseased plants I saw today looked beautiful – leaves were big, dark green with no yellowing – but there on the underside of some leaves was the characteristic spores of this pathogen.  Symptoms were just starting.  Within a few days affected leaves will start turning yellow and then eventually will die and drop from the plant, but not before the spores have been dispersed by wind to other leaves on the plant and to other plants in other gardens and farms.  Could be just like the 2009 late blight outbreak in the northeast.  

Basil downy mildew is a new disease (first reported in US in fall 2007) is one that I think is occurring every year throughout most of the US.  I am looking for help to see if I am correct.

Since I started monitoring the disease in 2009, I have gotten reports from 41 states, providing some evidence that I am right, but the number of reports is not enough to confirm this; for some states I have only one report, and sometimes the report was not confirmed.  No reports have come in from IA, ID, NE, NM, NV, OK, SD, UT, and WY – is this because the disease has not occurred there? or no one has reported it?

basil_dm8801x500As an avid gardener I know how popular basil is to grow, which is why I am turning to gardeners for help.  Downy mildew has developed on the few plants in my home garden in NY every summer since 2008 (am I the only one this unfortunate?!?).

The pathogen produces an abundance of spores easily dispersed by wind.  A related pathogen causing downy mildew in cucumber is known to move every year throughout the eastern US from south FL where it can survive through winter; both of these pathogens cannot survive in crop debris.  But other downy mildew pathogens do not spread so widely.  Another way the basil downy mildew pathogen gets around is in seed, which is most likely how it first came to the US.  There have been reports of affected plants in stores and garden centers, including this year.

Click here for photos, more information and links to my monitoring pages.

While I am looking for reports, other pathologists working with me on a national project want affected plants for their research on the pathogen.  So don’t despair if your basil becomes diseased – look at it has an opportunity to help further science!

Thanks for your help!

Dr. Meg McGrath  [email protected]


  1. As the biggest basil fan out there, I had no idea that this downy mildew could be an issue! I hope it’s not like the blight my little tomatoes suffered.

    But I try to shop at local nurseries and buy my plants from little roadside stands, avoiding the big box stores. Hopefully that helps! Thanks.

  2. My seed-grown basil plants came down with this for the first time last year. I bought replacement plants and they too developed it. This year, same thing, for both seed-grown and store-bought. Some of them survive, some don’t. I’ve grown basil from seed for decades and have never had any problem with them before. I am in southeastern Mass.

  3. This is really a very serious issue! I have read that mildew may look like nothing serious in the beginning, but it’s actually something very dangerous and deadly. There have even been cases in Australia, but nothing too serious. I hope you will be able to find a solution to the problem, because basil is something great, and life wouldn’t be the same without it.

  4. Well, that may explain why my first planting of basil failed this year. I bought the plants from a reputable indie garden center, but the leaves did indeed yellow and the plants died pretty quickly. The second planting is in a container on my patio, so hopefully they’re safe.
    I live in Pennsylvania and only recently have been plagued with downy mildew and powdery mildew on anything susceptible. Both appeared about 3 years ago and I’ve been battling them ever since. I use copper sulfate to control them and I’ve had pretty good success, as long as I stay on top of it.

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