Tomato Plant Diseases – How Much Do You Need to Know?

When you type “tomato plant diseases” into the Google search box, you’ll get over 550,000 articles about tomato diseases.

You could spend hours — even days reading of fungus based early blight, late blight, verticillium wilt, fusarium wilt, gray leaf spot, Septoria leaf spot, anthracnose, molds and mildews, mosaic viruses, bacterial spot, bacterial speck, bacterial wilt and an endless number of others.

There are some great articles out there and on some nice looking websites.  They’re set up to help you understand all the nuances of tomato plant diseases and what chemical (organic or otherwise) you should use to get rid of the problem.

There is a season and weather for every disease.  Some appear during early to midseason, in humid weather or after a period of heavy rainfall. Some appear in mid to late-season and strike in cool, wet weather. Others can show up at any time during the season. There is even one that strikes only one side of the tomato plant!

One Things for Sure

Tomato diseases are common to tomatoes! What gardener in the world has not seen a leaf at the bottom turn yellow and have brown spots?

We as gardeners are pretty much obsessed with our tomatoes and any disease that might turn up on them. I include myself in that –because as I have mentioned many times in my posts I spent a lot of time in my early days of gardening worrying about what kind of diseases my tomatoes had. (You can read more about that here.)

I think as a gardener, one will always have the feeling of wanting to know what’s causing the problem, but I override the feeling to spend even part of an hour looking for details about diseases.

When I started gardening 35 years ago — I just had to push forward no matter what happened and trust that I would get a good crop.  There wasn’t much else I could do no matter how bad the yellow leaves got. We had no money and no way to get any other information other than what I read in my Organic Gardening Magazine.  It certainly worked for good, because I’ve had 34 years of great tomato harvests without all the specifics of what caused a leaf to yellow, etc.

A Healthy Garden (healthy soil) is your best Defense

Even healthy gardens can have tomato plant diseases. BUT – plants in a healthy garden can withstand the attack and keep right on going and give you an abundant harvest.

Many folks recommend all kinds of sprays.  That’s not necessary.  I’ve never sprayed my tomatoes in almost 35 years of gardening and always have abundant harvests.

Unless researching tomato plant diseases is something you consider fun and you have the time to spend on giving it priority — I can tell you — you don’t need to do it.  And here’s why.

Every tomato plant disease can be either avoided or lessened by consistently following fundamental, good gardening practices

Here are 14 guidelines:

  • Continually improve your soil and replenish the organic matter.  Organic matter in the soil is the best thing you can do to fight diseases.
  • As you continue to improve your soil it will settle at a ph level of about 6.8 (at least between 6.5 and 7) Most vegetables including tomatoes grow best and are healthier at this ph.
  • Good drainage (which comes with proper soil preparation and improvement) is a necessity for tomatoes as well as most other vegetables.
  • Give tomatoes space for good air circulation.  Their leaves should be able to dry quickly after heavy dews and rainfalls.
  • Staking  your tomatoes also improves air circulation and keeps them off the ground to avoid pathogens getting on the leaves — especially during rains.
  • Mulch you soil to keep needed moisture in and to keep pathogens from splashing onto leaves.
  • If you water — (I don’t) — be sure to water at soil level and DON’T OVER WATER!! Over watering is as bad for a plant as not having enough water.
  • Grow your own seedlings. Your own plants  or those from an organic grower will be much stronger than those raised with a diet of artificial chemicals.
  • Remove and destroy any leaves that you think are diseased.  Usually it starts with the bottom leaves and removing them can keep or help keep the disease from spreading.
  • Don’t handle your plants when they’re wet.  Leaves can be damaged easily this way and diseases can spread.
  • All sources I’ve read indicate that if plants are diseased do not compost foliage or leave them in the garden.   If your compost pile is hot enough it will probably destroy the disease pathogens. (Update 2023) This is a good recommendation, IF there is really a disease.  I have long ago stopped thinking that every brown or yellow leaf is a diseased one.
  • Make sure your tomatoes get plenty of sun.  Eight hours is ideal.  And all day is ok.
  • Don’t let smokers in your garden.  If you’re a smoker — wash your hands good before going into the garden. Tobacco can carry the tobacco mosaic virus.
  • It’s hard to rotate crops in small gardens.  But do the best you can not to plant tomatoes where other nightshades (potatoes, eggplant or peppers) were previously grown.

Final Thoughts

If you consistently follow these gardening fundamentals, you can rest assured that tomato diseases will most likely decrease with each  passing year in your garden.  Just remember that every year has different variables and not every leaf that is mottled, yellow, or brown is carrying a disease.


Organic Gardening is easy, efficient, and effective — and it’s a lot healthier.


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  • Hi Theresa!
    It is very interesting that you don´t recommend overwatering your tomatoes (or not watering at all), since the tomatoes are believed to be heavy drinkers; especially when the fruit are forming and ripening. I suppose, this is one of the reasons, why self-watering containers (SWC) are so popular among tomato growers.
    We tried growing tomatoes in SWCs one year, but were rather dissapointed with the results – the flavour seemed to be less intence, less sweet and a bit watery…

  • Hi Kiskin — Just to clarify — I don’t water any of my garden because I’m not and never have been set up to water. There is nothing wrong with watering IF you water correctly. Even heavy drinkers don’t like being overwatered. (I’ve written quite a few posts on that.) Most people seem obsessed with watering and thus, they overwater. One is just as bad as the other.

    A lot of all this watering, spraying, thinking you have to have sides for beds, etc. is all marketing. I’ve been gardening organically and very successfully for 35 years and never used any of that stuff. (Just something else to buy in my opinion.)

    Really appreciate your thoughts on the self watering containers. I’m not familiar with them.

    Thanks for commenting Kiskin.

  • Yes Theresa, You really can spend a lot of time trying to puzzle out what the yellowing leaves are all about. I know I have! And.. since I’m not going to spray any chemicals regardless, there’s usually nothing to be done at that stage except remove the leaves as you say.

    I discovered this year what a really healthy tomato plant looks like (thick stemmed, very green, stocky) as opposed to what I’ve thought in years past (tall, fragile-stemmed, greenish) so I can’t thank you enough for your posts on soil prep. I think that’s made all the difference. You always stress the soil, and you’re right!

  • I appreciate the confirmation Sandra.
    The more I read, and the more I hear, I know new gardeners especially are taken in with all the hype —- when actually everything is so simple.
    Improve your soil and let nature do the rest.
    I’m thrilled about your tomatoes looking so good! Can hardly wait to hear about your bumper crops.

  • Sides to garden beds aren’t about commercial hype for me. It’s about keeping my husband from running over everything with the lawn mower. We have our first lawn and a new lawn mower. He got a string trimmer, too, and the first time he used it, I got a huge bouquet of Sweet William, courtesy of his learning curve.

  • Congratulations on your first lawn AND the new lawn mower. String trimmers are great — but take a bit of getting use to.
    You made a great point for sides to garden beds for some folks.
    Thanks for sharing.

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