Cucumber Fungus

Asked August 11, 2020, 10:37 AM EDT

One of our clients sent the following message and photos. Can you help or let me know who can? Thank you! Jan Sweet, Office Manager MSU Extension - Chippewa County 319 Court Street Sault Ste Marie, MI 49783 906-635-6368 906-635-7610 (fax) The ground that my cucumbers and tomatoes are planted has a fungus. I read treating the ground with baking soda and wetting the soil would possibly kill the fungus. I did that last fall three times making sure the ground was throughly stirred and saturated with the soda and water. Shortly after the plants started growing I noticed they again had fungus. I googled how to save my plants. It said to treat the plants twice a week with a mixture of 3 percent hydrogen chloride with nine parts water. I did this religiously all summer. My cucumbers are already turning yellow and although they are loaded with flowers we have had very few cucumbers. I cannot plant in any other area as that is all the ground I have. Could you give me some insight on what I am doing wrong and what I should do. Thanks

Chippewa County Michigan

1 Response


Thank you for using the Ask an Expert service. There is a lot to go over from your comments.

I would NOT recommend treating the soil with baking soda. I do not think it will have the effect you want (killing harmful fungi) and might even harm the plants you’re trying to help.

Baking soda can work to slow or stop fungal growth in controlled environments by lowering the pH of the area, but it does not kill fungi and has much more mixed efficacy in less controlled environments, such as outdoors. I think baking soda would be especially ineffective at slowing fungal growth in soil, because soil is such a complex environment with many different pockets of material and spaces, and it can be difficult or slow to change the soil pH. Even if you could raise the pH of the soil easily, you likely would not want to, depending on the current pH of your soil. Most plants grow best at a near neutral pH of 6.5-7 because this is when the most nutrients are available to the plants from the soil. Plus, the sodium in sodium bicarbonate (baking soda) is toxic to plants, so you do not want to add more of it in your planting area.

Please read this article on the question of whether to use baking soda to fight fungi:

Baking soda - will fungi fail and roses rejoice? From Dr. Linda Chalker-Scott at Washington State University

You might want to consider getting a soil test to determine whether your site has the proper nutrients for vegetable growth and learn what the pH is. Visit for more information. Also, are you using fertilizer on your vegetables?

It is possible that a pathogenic fungus might overwinter in your soil on plant debris. There are a few non-chemical ways that you can reduce the build-up of fungal plant pathogens and reduce the amount of pathogen that makes its way onto the upper part of the plant.

Of course, you could replace some of the soil in the beds you are using, although this might be costly and difficult. It might be easier to add a layer of organic mulch, such as dried, ground-up tree leaves, around your plants, to prevent pathogens from the soil from splashing up onto the upper parts of the plant.

Article: Mulches for the Home Vegetable Garden from Virginia Cooperative Extension

You can also consider planting your vegetables in large (5 gallon or more) pots next year with new, store-bought potting media.

Also, water at the base of the plants, and practice good spacing and pruning to improve air circulation and keep the upper parts of the plants as dry as possible. When the upper parts of the plants stay moist for longer periods, they develop disease more quickly.

Removed potentially diseased vegetable plant material from the garden area and dispose of it in the municipal trash, through burning if permitted and safe, or in a hot compost. Do not add it to a compost that will be used on a vegetable garden later.

Finally, are your plants getting fun sun? This could affect fruiting.

Now to your comment about how “Shortly after the plants started growing I noticed they again had fungus. I Googled how to save my plants. It said to treat the plants twice a week with a mixture of 3 percent hydrogen chloride with nine parts water. I did this religiously all summer.”

We recommend only using chemical control options after you have tried other non-chemical disease management strategies and then identified the pathogen(s) that you have, if possible. If you know what types of pathogen you’re fighting, such as a fungus, bacteria, or virus, you can choose the most effective treatment option. It is also possible that the main issue is not a fungal pathogen.

It is not obvious to me from the photos you sent whether there is a fungal pathogen present. I cannot see the leaves closely enough. I mostly just see some yellowing on the leaves. Since you’ve had issues for a couple of years, you can consider sending some samples of the plants that you think have a fungus to MSU Plant & Pest Diagnostic Services. I would suggest taking some more close-up photos and sending them to the lab along with the other more zoomed-out photos, before sending in the samples. Please visit the website for more details:

I would also recommend that if you’re going to use a pesticide product, such as a fungicide, use one labeled for use on the plants that you want to treat (tomatoes and cucumbers) and against the pathogen that you’re trying to fight. Follow all label instructions. The label is the law, and label instructions are meant to keep you, the plants and the environment safe. They also help you use the pesticide in the most effective manner.

Here are a couple of publications that could be helpful:

Home Garden Fungicides from U. of Wisconsin-Madison

Homeowner’s Guide to Fungicides from U. of Kentucky

Now to discuss what you’ve been doing this summer. I would recommend following advice from .edu, or possibly .gov or .org websites. I’m not sure where you found the information that you did. Correct me if you find that I’m wrong, but I have a feeling that you weren’t actually using hydrogen chloride, which is a gas a room temperature, but instead a solution of sodium hypochlorite or bleach. I would NOT recommend this. For one thing, it’s not labeled as a pesticide for use on plants. But also, it is likely to harm your plants. In another article from Dr. Linda Chalker-Scott at Washington State U. she mentions how she would NOT recommend using bleach on pruning wounds, since it’s “extremely phytotoxic” a.k.a. harmful to plants. So, the solution you’re using actually might be causing some of the problems.


The Myth of Chloroxed Clippers From Dr. Linda Chalker-Scott at Washington State University

Also check out our Vegetable Gardening webpage on the the MSUE Gardening in Michigan website. Note the article on Integrated pest management in vegetable gardens.

I know that’s a lot of information, I hope that some of it helps!