Yellow basil with brown spots

Asked August 18, 2016, 8:39 AM EDT

I've tried googling why my basil leaves are yellowing and have brown spots, but I can't tell if it is one of the bacterial infections or if it is due to lack of nitrogen in the soil. I've attached a picture. I have a very large crop of basil and I'm afraid that I may have to pull them all out :( Thanks for your help!

Anne Arundel County Maryland downy mildew herb basil decline

6 Responses

We think this just looks old and tired. You could clip off the old leaves and see if it sprouts anew, but it just may be the end of the season.

cm

FWIW, the underside of the leaves look "dirty". I'm starting to think it's downy mildew. I've trimmed the basil back and lots of new growth is stimulated, but as soon as the leaves start to mature, they turn yellow, have these brown spots and get this dark, dotty film (the mildew?) on the underside. The entire crop has been affected (the more newly planted basil as well as the older crop). Can I prevent this in coming years?

Based on your description this sure sounds like downy mildew.
If so, this is our first case for this year, which is better than in years past. It really hadn't been a problem around here until a few years ago.
Here is our page (from last year) with photos and more information: http://www.extension.umd.edu/growit/downy-mildew-basil

It is not supposed to be able to survive winters here, but clean up fallen leaves and debris and get it out of your yard.
Our vegetable specialist suggested starting your own next year from fresh seed.

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Will this kind of mildew affect the other plants in my garden? (tomatoes, eggplants, pumpkin, peppers, zucchini, beans, peas?) Should I pull all of the basil up now and not wait for the end of the growing season? Is there a way, if it survives the winter, to remove it from the soil (like keep that area fallow or plant another crop there next year)?

.... and a follow-up. Should I use a different seeds than the one I used this past year? I'm not sure how they got downy mildew in the first place. Is it from the seeds? No one close by has a garden or anything, so I don't know how the "infection" started. Thanks!

It can come into your garden on seeds, seedlings, etc. so we would recommend getting your seed from a different supplier.
The good news is that no, it should not bother your other crops.

We would suggest pulling it up and cleaning up all debris now as it will only get worse.
As we said, it is not supposed to survive the winter, but growing it in a different spot or in a pot is not a bad idea.

cm