Sunday, November 1, 2009

Ack! Tomato Leaf Spot

I knew it was too much to hope for ...

This morning, while I was watering, I noticed discoloration on the lower leaves of one plant. When I looked closer, I saw that the discoloration had spread throughout all the lower leaves of the plant—and I officially had a problem on my hands.

I took the leaf to a friend who farms tomatoes professionally and he confirmed what I suspected: I've got fungus. There are many fungi that affect tomatoes, and I don't know exactly which one this is, but I treated anyway. I first removed all the affected leaves on the plant, bagged them and threw them away. Fungus and bacteria can be highly contagious, so you have to be careful when you're handling infected leaves.

Then I treated every plant with a copper fungicide, which treats for fungus and has some antibacterial action. My friend recommended I also used Maneb, which is a stronger fungicide, but I'm going to hold off for now on that. Copper fungicide is rated for organic growth, and I want to keep my grow organic if possible.

But why did this happen? I've been careful, right?

I have a few thoughts on that. First off, the affected tomato plant gets less sun than I would like. I'm growing along the side of my house, and the winter sun is dipping too low on the horizon, so my neighbor's house shades these tomatoes throughout part of the middle of the day. In all, they're lucky to get three hours of direct sun, and that's just not enough. Second, and most important, my neighbor's sprinklers overspray onto this plant, and he waters in the middle of the night. So these plants were getting wet in the night. Finally, it's still too hot and muggy—these are perfect conditions for fungus.

Fortunately, this problem was not too widespread yet. The container tomatoes get much more sun—five to six hours of direct sun—and they are situated a ways away from the sick plant. So I'm hoping I can control this until the weather cools off and the affected plant gets tall enough that it grows back into direct sun.

Besides the obvious—lots of sun, don't let them get wet from above—this was a good reminder of another thing to keep in mind: it's always good to pay close attention.


  1. tomato growing is complex, having it been my first year last year, I have alot to learn, i tried setting up my own website and writing my own content just to reassure myself of what I know.

  2. Gavin,

    I know what you mean ... I've learned a lot this season by trying things I've not done before, or at least doing straight-up comparisons. I checked out your site. It's nice!


  3. The product in the link is perfect for tomatoes. You should look into it. It naturally kills insects and fungal problems. It can also be sprayed up to the day of harvest. The Garden Rebel talks about it every once and a while.

  4. I would like to offer my two cents worth. First of all you are playing russian roulette by buying a plant from almost any commercial non-organic source. You simply do not know anything about how the plant was grown or with what. They are saturated with chemical fertilizers. Growing conditions are not optimal in any respect so you are starting off with 10 strikes against you at the beginning. They are stressed from the very beginning and will "catch" any disease that comes along. Stressed plants attract harmful insects - healthy ones do not.
    Another question you want to ask yourself is was this grown near gmo fields? Do you know what the long term affect of a genetically modified product is to your body? Or the tons of roundup pesticide they use to grow them?
    Secondly it would seem that most home gardeners would be interested in growing a plant that would provide them with optimal nutrition.
    I use the BRIX method ( This is simply an awesome growing system. But I had one weak spot. I was using organic commercial potting soils. They introduced disease into my garden and it spread like wildfire.
    So I am thanking you prodigiously for pointing to this coir system. I am very excited to try it. Also their new pesticide looks promising.
    A note for newbies - organic pesticides are strangely regulated - many have extremely toxic ingredients so beware of "natural" claims - research ingredients to see if they are really non-toxic. Many organic pesticides kill beneficial insects are quickly as the harmful ones. Many kill bees.
    Another great product for getting rid of disease that has been introduced is to use food grade hydrogen peroxide. Which also adds additional oxygen to your plants.