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One of the plants in the garden developed brown yellowish spots on the leaves. All of the infected leaves are high. The bottom ones show no illness.

We've had lots of rain, followed by extreme heat. Relative humidity is 60% at 34 C. Is this Septoria Leaf Spot?

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If the infected leaves shown are the same as other infected leaves, I'd say this is septoria leaf spot. The weather conditions prior were ideal for the fungus to grow. Usually the lower leaves are infected first but since you've mulched with straw, soil (that contains the fungus) splashed on lower leaves has been prevented.

Early blight has concentric (round) spots that develop first and is easy to distinguish between septoria leaf spot. Tomatoes can be affected by both so check over your plant. But be careful not to touch uninfected leaves if you've touched those infected ones! The fungus can be spread that way.

Both How To Identify and Treat Septoria Leaf Spot and Septoria Leaf Spot of Tomato have good advice. I tend to err on the side of caution. When removing infected leaves, I'd use disposable gloves (mine are nitrile) on the left hand to grasp the infected leaves and sharp clippers or even scissors to cut the leaves. If I have to push past healthy leaves to clip infected ones, I'd have a cup of hydrogen peroxide with me to dip the clippers in after each cut to minimize any chance of the fungus spreading. But then, I can be a bit fanatical about my plants.

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    Excellent advice, Jude. Do you have a vegey garden going with tomatoes? What varieties are you using? Pruning to do good usually only spreads disease more. I use alcohol instead of H2O2. If only people saw all the spores available to infect vulnerable plants they would be erring on the side of caution as well. Your point on his mulching is perfect to explain why the lower leaves weren't infected firstus.
    – stormy
    Jun 23 '17 at 19:18
  • I wish I did but no. I had a huge vegetable garden at one time, prize winning too. The last place I had was sold when I couldn't keep up any more. Needed repairs too - couldn't afford it. Wasn't good for a garden as mainly shaded, plus my wild 'pets' visited me regularly. They're hard on plants (my avatar is one visitor). Living in a condo now but it's only for a few years. Was supposed to get a small garden plot but never happened so I gave my Early Girl and another early one (forget the name) to a good friend and we'll harvest together. I'm teaching her about gardening and plants.
    – Jude
    Jun 23 '17 at 21:54
  • Only tomatoes grown in a greenhouse do well here. All are badly affected by late blight so home gardeners need to use earliest varieties possible to have some tomatoes before it hits. Come August, it's hot with little rain but nights are cool and humid and fungal diseases thrive. Powdery mildew's evident on many plants including trees. 10 months of rain and 2 months of drought best describes the climate here.
    – Jude
    Jun 23 '17 at 22:04
  • Blight taught me a huge lesson decades ago! I am sorry you lost your home. If it helps, I lost 2 homes in 2008. Banks are very very bad. I am trying a new greenhouse tomato variety, Applegate. Indeterminate major vine type that will need special staking. Supposedly the most flavorful of the 'green house' varieties. I'll let you know. I love raccoons. They are hard on chickens as well. Come out to find a perfectly autopsied chicken with organs all arranged and grouped with precision. No chicken left of course. Love raccoons! Can you keep them out of your greenhouse?
    – stormy
    Jun 24 '17 at 17:26
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    The only solution I have found is to mulch with a lot of dried grass clippings to prevent splash up. When I keep up with it, I have zero issues. If I slack, it appears.
    – Evil Elf
    Jun 26 '17 at 12:41
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I had the same problem. Maybe this can help you: Septoria leaf spot, or Septoria lycopersici, is a fungus that looks like gray or brown spots surrounded by yellowed areas, and usually starts at the lowest leaves. Do what you can to reduce moisture in the area by removing affected leaves, watering the soil without wetting the leaves, and doing what you can to increase air movement to help evaporation. Be careful not to cross-contaminate. Use a fungicide.

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  • Link-only answers are discouraged here. Kindly explain the OP why and how the link you gave can help.
    – J. Chomel
    Jun 26 '17 at 11:34
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this is Septoria, looks like it anyway, just cut off diseased leaves before watering again. Before turning on your fans. This is exactly why I am unable to imagine tomatoes being perennials. If there is a disease they will get it...they always get so diseased by so many vectors that it just feels better to get rid of the plant after harvesting. Clean up debris very well and wait for at least 2 even 3 years before planting tomatoes or any of the nightshade family in that same soil.

Supposedly the bottom leaves are infected with septoria before the middle and upper leaves. I don't think they were infected from the soil beneath, rather the dust in the air landing on a damp leaf.

Once a plant is infected with a fungus it is a done deal. With one exception; powdery mildew. I am waiting for your question on this fungus a month from now! Powdery mildew can be treated (9:1 water/milk) after infection.

Septoria can not be treated. For this the best you can do is cut off infected leaves, thin your plants for more ventilation and get a fan blowing your plants so that you can see the tomato plants moving. Use alcohol on your pruners. Dispose of all debris. Use a bagged compost to cover soil near your tomatoes.

This is so normal. Just keep cutting. I usually give up towards the end of the season. I dump potato and tomato debris in my compost pile that is far away and down wind to my garden. That compost will never be used in the vegey garden ever.

Your pictures of your plants show very healthy plants and looks like you are getting a great harvest, yes? The healthy leaves look wonderful. I usually have wimpy plants at the end of the year anyway and thus very susceptible to Septoria and powdery mildew. Well, there just is no such thing as a perfectly healthy tomato plant...at least I have seen one without some sort of disease. Never.

Perhaps you could take a picture of your entire crop? What are the varieties? Were they resistant to any diseases, should say on the packets of seed. I am trying to grow Applegate tomatoes. They grow in grape-like clumps only the tomatoes are 2". And this brand is designed for the UV spectrum in a greenhouse yet tasty. I guess tomatoes made to grow in a greenhouse aren't very flavorful.

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  • haha, I wont hesitate to take a photo of powdery mildew :) sure, I will take a photo in the morning. It is getting dark over here. These plants are outside, still waiting for the provisional roof. I will ask my parents about the varieties, because they did the seeding part.
    – sanjihan
    Jun 23 '17 at 19:23
  • Bamboo turned me onto this milk and water spray and I was amazed how well it controlled powdery mildew. 9 parts water; 1 part milk. Skim milk works fine.
    – stormy
    Jun 23 '17 at 20:35
  • imgur.com/a/j4cML There you go. Normal plant, next to the one infected. I am still working on varieties. What might be of more interest to you is this guy: imgur.com/a/TIx8g. It's growing tip was pruned, and the new 3 growing tips, were also pruned of after a while. result ->around 10 growing tips and over 50 tomatoes. Small, but they are growing. No diseases so far
    – sanjihan
    Jun 24 '17 at 19:11
  • Milk and water (plus I'd add a pinch of baking soda) is what I use to use on my ornamentals when I first noticed powdery mildew. Has to be used as soon as symptoms appear. I'd sometimes miss it at first so I'd pick all affected leaves off then spray. New growth would be healthy. Needs to be reapplied as needed or after a rain. I use reconstituted skim milk. I experimented with adding a bit of dish detergent too so spray would adhere better. I'd experiment on non-essential plants with different methods to control insect pests and fungal diseases after doing research on them. Most worked well!
    – Jude
    Jun 26 '17 at 17:45
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    Yes, powdered milk. I keep it with my kitchen staples for baking. (I've been more active on Seasoned Advice SE and it's what I consider a kitchen necessity.)
    – Jude
    Jun 26 '17 at 18:57

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