Symptoms Of Tomato Blight, Powdery Mildew and Black Spot

The most common fungal infections, blight, powdery mildew, and black spot, can be devastating in your vegetable garden, flower garden, or fruit trees. Here’s a primer on symptoms and prevention.


Consistently wet, humid, or damp weather creates a perfect environment for fungal infections of plants. Fungi spores grow rapidly in persistent moisture and at the very least create stress on the plant, leaving them vulnerable to secondary infections. Early prevention is the best defense, because once you actually spot symptoms, it’s usually a losing battle. Here’s what you should look for:

powdery mildew

Powdery Mildew infested this pumpkin in just a few days

Symptoms of Powdery Mildew: White or gray powdery spots on the stems and leaves of your plants, which grow larger every day. Preventative treatment: Baking Soda Spray or milk spray

Symptoms of Black Spot: Affects roses and fruit trees and is very common in apples and pears. As its name implies, the disease starts as small black spots on the tree’s leaves which grow larger as the season progresses. Black Spot frequently spreads to the fruit bud as well and will show on the fruit as it matures, resulting in a fruit neither pleasing to the eye nor the taste buds. Treatment: any solution which contains copper sulfate or copper hydroxide, sold under various brand names

Black Spot infection in pear tree

Black Spot infection in pear tree

Symptoms of Tomato Blight: According to Rodale’s Pest And Disease Problem Solver: “Leaf spots are the first symptom of early blight. The spots are brown with a concentric target pattern…they usually appear on oldest leaves first. Spots enlarge and run together…Dark, sunken lesions appear on the stems, often starting near the soil in young plants.” The leaves yellow and fall off, lowest ones first and the fruit becomes discolored.


homegrown tomatoes todd heft

Click to learn the secrets of growing organic tomatoes in your garden


To avoid Tomato Blight, follow these guidelines:

  • Plant heirloom varieties: These tomatoes are decades old or more, and have survived many diseases and weather extremes. They may not be immune to blight, but they stand a better chance of surviving it.
  • Use mulch under your seedlings. Mulch suppresses fungal spores which may have overwintered in your soil
  • Plant varieties well adapted to your area.
  • Plant varieties resistant to blight. These would be marked as LB (late blight resistance) and AB (Alternaria/Early Blight resistance) on the plant tags at the nursery.
  • Leave more space than usual between your seedlings. Air flow is essential for helping plants to dry quickly after a rain storm. If the plants spend less time wet, they’ll be less susceptible to blight infection.
  • Plant your tomato seedlings on the opposite side of the garden from where blight occurred previously.

Treatment: same as Black Spot above.

If you suspect any symptoms of tomato blightpowdery mildew, or black spot, treat your plants immediately. The earlier you treat the plant, the more likely you’ll get the fungus under control. It’s always a good idea to treat at the first report of symptoms in your area, even if you haven’t yet seen any symptoms yet in your own garden.

About Todd Heft

Todd Heft is an organic gardener and freelance garden writer who lives in the Lehigh Valley, PA and has gardened for most of his life. When he isn’t writing or reading about organic gardening, he’s gardening. His first book, “Homegrown Tomatoes: The Step-By-Step Guide to Growing Delicious Organic Tomatoes In Your Garden” is available on Amazon now.

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4 Responses to Symptoms Of Tomato Blight, Powdery Mildew and Black Spot

  1. Dionaura says:

    i love your blog, don’t find many that are so clear, it is nice to see that someone really understands.

  2. Paulo says:

    It’s been a late year for temotaos here in Northern California, so my Early Girls have been my stalwarts.

  3. dee says:

    Very informative! I will make sure to check the leaves on my tomato plants as they mature. Thanks!

  4. Great tips! Thanks for sharing!!