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?
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.
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.
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.
