How to fix brown leaves on tomato plants

Inhaltsverzeichnis Show

Stake or trellis your tomatoes.
Don't work in tomato plants when the leaves are wet.
Make sure air circulates well around plants.
Rotate crops.
Should you use a fungicide?
Most home garden tomatoes do not need to be treated with a fungicide.
When to stop fertilizing tomatoes
Watch for tomato horn worm
Why is my pepper plant so small?
Eat zucchini, squash blossoms

Staking and mulching plants and pinching off infected leaves help keep leaf spot diseases in check.
Improve air circulation around plants.
Keep leaves dry by watering at the base of the plant.
Do not save seeds from infected plants.
Leaf spots should not affect the amount of fruit your plants produce.

There are three leaf spot diseases commonly found on garden tomatoes in Minnesota: Septoria leaf spot, early blight and bacterial spot.

Young tomato plant with leaf spot disease on lower leaves

At the earliest stages of disease, they are difficult to tell apart but the management practices listed below will work for all three disease problems.

Most tomato leaf spot diseases overwinter in the soil and then splash on to the lower leaves of the plant. As a result, the first leaf spots can be found on the lowest leaves closest to the ground.

Look for brown to black round spots that are the size of a pencil tip or larger.

Bacterial speck is a disease that is similar to bacterial spot. Bacterial speck and spot can cause spots to form on the leaves, stems and fruit of tomato plants.

The leaf spots caused by bacterial speck and spot look identical but you can tell them apart by the different types of fruit spots that form later in the season.

Speck infections on fruit are small (the size of a pencil tip) raised black spots.
Bacterial spots on fruit are larger (the size of a pencil eraser end).

Do not can tomatoes infected with bacterial speck or spot as these diseases can change the pH of the fruit.

Septoria leaf spot on a tomato leaf

Pinch off leaves with leaf spots and bury them in the compost pile.
It is okay to remove up to a third of the plant's leaves if you catch the disease early.
Do not remove more than a third of the plant's leaves.
Keep leaves dry to reduce spreading the disease.

Each leaf spot produces hundreds of fungal spores or bacteria that can be splashed or blown onto other leaves, resulting in even more leaf spots. Under the right weather conditions, these new leaf spots produce more spores or bacteria in as little as two weeks.

This cycle can repeat throughout the summer, resulting in brown blighted plants. By removing leaf spots early, you slow the spread of the disease through the plant.

Many gardeners will remove the lower third of the leaves on every plant whether they have leaf spots or not. This makes it harder for plant diseases in the soil to get splashed on to the lower leaves.
Removing lower leaves also improves air circulation around the plant and allows the leaves to dry quickly after rain or irrigation.
Fungi and bacteria need moisture on the leaf surface to start a new infection, so keeping leaves dry is important.

Stake tomato plants, remove lower leaves and use landscape fabric to reduce diseases.

This will reduce the ability of diseases in the soil to splash onto the lower leaves.
Landscape fabric, straw, plastic mulch or dried leaves are all acceptable mulches.
Tomatoes are sensitive to many herbicides used in lawns. Don't use grass clippings or leaves from a lawn that has been treated with an herbicide.

The fungi and bacteria that cause leaf blight need moisture on the leaves to start infections, but tomatoes only take up water through their roots.

Keep the water in the soil where the plant can get it.
Keep the leaves dry to reduce problems with plant disease.
Use drip irrigation or a soaker hose or direct the garden hose at the base of the plant.

Stake or trellis your tomatoes.

This will increase air circulation around your plants and help leaves dry quickly after rain or irrigation.
Staking and trellising can reduce the amount of fruit rot on tomatoes.

Don't work in tomato plants when the leaves are wet.

Under moist conditions the bacteria reproduce and easily stick to hands and tools.
Wait until plants are dry for chores like staking, pruning and weeding to reduce the spread of the bacteria.

Make sure air circulates well around plants.

Providing good air movement around the plants by staking or caging tomatoes, pulling weeds, and spacing plants far apart will allow leaves to dry quickly.

Rotate crops.

Allow two years to pass before planting tomatoes or peppers in the same location.
Do not save seed from infected plants.

Should you use a fungicide?

Most home garden tomatoes do not need to be treated with a fungicide.

Tomato plants can tolerate high levels of leaf loss from leaf spot diseases without affecting the number of tomatoes produced by the plant.

Use cultural control practices like staking and mulching plants, and pinching off infected leaves to keep leaf spot diseases in check.

There are yellow and brown leaves on the bottom of this tomato plant, but that’s normal. Photo by Connie Oswald Stofko

by Connie Oswald Stofko

The leaves on the bottom of my tomato plants are turning yellow, then brown.

Don’t worry; it’s normal, says Jen Weber, vice president and manager of Mike Weber Greenhouses at 42 French Rd., West Seneca.

“That’s what happens when the plant starts making tomatoes,” she said. “It’s better to have an ugly plant with lots of tomatoes than the other way around. By the end of summer, you should have a dead-looking tomato plant.”

That’s what mine always looked like, and I thought I was doing something wrong!

If those ugly, dead leaves bother you, you can snip them off.

But if half of your plant has dead leaves at this time of year, it’s probably because you under-watered it, over-watered it, or dumped too much fertilizer on it, she said.

If you think your tomato or other plant might really have a disease, you can stop in to Mike Weber’s to ask. The best thing to do is to use your phone to take a photo of the diseased leaf or other affected part of the plant, Weber said.

If for some reason you can’t take a photo, you can snip off a leaf or other part of the plant that you believe is affected, but leave it in the car! Don’t take a possibly infected leaf or part of a plant into Mike Weber’s — you could be spreading disease onto their plants! Just tell them you want to show them what you think is a diseased plant and they will go out to your car to look at it.

Hours at Mike Weber Greenhouses are 8 a.m. to 6 p.m. Monday through Saturday and 9 a.m. to 6 p.m. Sunday.

Weber shares more on tips on vegetables below.

When to stop fertilizing tomatoes

Stop fertilizing tomato plants once they start to flower, Weber said. If you keep fertilizing, you’ll get a big plant, but no tomatoes.

Tomato hornworms can be hard to spot, but if you see one, pick it off before it noshes the plant down to the stems! Photo courtesy Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org

Watch for tomato horn worm

Now is the time to watch for the tomato hornworm.

“It looks like a friendly green caterpillar with a thorn on his head,” Weber said, “but it will eat your plants down to the stems!”

They’re hard to spot at first. In the photo, you can see that they blend in with the tomato leaves.

When you discover them, the best thing to do is pick them off, she said.

Tomato hornworms aren’t worms; they’re caterpillars. They bury themselves in the ground and come out as a moth.

Why is my pepper plant so small?

If your pepper plant is smaller than it should be, it’s probably because you put it outside before the night temperatures were warm enough, Weber said.

Peppers need night temperatures — not daytime, but night temperatures — of around 65 degrees Fahrenheit, she said. It didn’t get that warm until July.

“With our cold, wet spring, we lost about a month, temperature-wise,” she said. “We’ll have late vegetables this year.”

And if you’re one of the gardeners who put your peppers outside on Mother’s Day to get a jump on things, you were way too early. That’s why Weber tells gardeners to wait until the beginning or even the middle of June to put peppers outside.

“You never know” what the weather will be like, Weber said.

Eat zucchini, squash blossoms

If you’re blessed with a bumper crop of zucchini or other squash, consider eating the flowers, too.

The flowers are edible, and there are a lot of recipes online for stuffing and frying zucchini blossoms. Weber likes to bake them.

Of course, there are a zillion recipes for zucchini, too, and if you make a big batch of zucchini bread, you can freeze it for the winter.

But if you’re running out of ideas on how to use all that zucchini, try eating the blossoms instead of the fruit. It’s like getting two different foods on the same plant.