What’s causing brown patches on my basil leaves?

Question

My basil always does great every summer in pots on my balcony in Chicago. But the last couple years around September the leaves start to develop large brown patches, both in the center of some leaves and along the edges of others. This fall is the worst I’ve ever seen. I always try to bring my best basil pots indoors before the first frost so I can use some in the winter, but the last few years the leaf destruction worsens within a week or two after bringing them inside and I have to throw them away. In the past, I suspected damage from thrips but now I’m wondering if it’s basil downy mildew. It has been spreading among different pots. What looks to be the cause of this and how can I prevent it next fall?

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Answer 1

Basil plants are bad about getting infections, pretty quickly. This is especially true once they are brought indoors. They are sensitive to staying wet for too long, and indoors they tend to take longer to dry out.

The trick will be to only water once the soil is completely dry down to 3 inches. This could take a week, two weeks, or just a day or two depending on the conditions in your house.

If you use the same pot over and over, you will want to sterilize it between plantings. There are many ways to do this, so clean them with what ever is available to you. If you use a harsh chemical, just be sure to wash it off with water, thoroughly.

Treating with a fungicide can help, when you see early signs of infection. This article will help:

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

Here is an article that will help you to grow basil indoors: https://www.gardeningknowhow.com/edible/herbs/basil/information-on-how-to-grow-basil-indoors.htm