tomato diseases

One of my two mature, productive tomato plants wilted last week. Surprise! My previous article (was it just five weeks ago?) about wilting tomato plants was more timely than I knew.

This is the story of what happened.

We had rain. The rain in our area has been patchy, so the rain in my yard may not be like the rain in your yard, but one day we had about 10 hours of steady rain. When I looked out the front windows the next morning, thinking that the garden would probably look great after all that water, I saw that one of my tomato plants had wilted.

I thought back to my previous article about the steps to follow, to figure out what happened to my plant.

At the very least, I can say with confidence that dry soil was not the cause of the wilting.

The plant hadn’t wilted only on one side, and it wasn’t merely slightly droopy. All the leaves on the entire plant were hanging limp on the branches, and smaller branches were sagging.

At first, I thought “cool, bacterial wilt”, since the wilting was so sudden.

Checking for Bacterial Wilt

This is a disease I have seen only once, but I knew that one sign of bacterial wilt was sudden wilting of the entire plant.

Often, this wilting takes place in hot weather and moist soil.

I trimmed off leaves and branches to do the bacterial wilt streaming test. If bacterial wilt was the cause, then white cloudy ooze should stream out of the branches when they were suspended in water.

When the first couple of leafy branches failed to produce the white cloudy streaming that I expected, I cut a thicker section of stem to add to my jar of clear water, to see if maybe I just hadn’t used a big enough section of branch. Ten minutes later, the water was still clear.

Looking at base of the plant for more clues

Then, I finally looked at the base of the plant, where the stem emerges from the ground. This was when I thought “uh oh”. There was white fungus-looking stuff right near the base of the plant and climbing up the stem.

To be honest, this is probably a bigger problem than bacterial wilt would have been for the future of my garden. My knowledge of white fungus climbing up stems from the ground leads me to think the fungus is Southern Blight. (Link is to a pdf about Southern Blight from University of Kentucky)

Lots of fungal diseases are host-specific. That means that they can infect only a limited number of crops. Southern Blight, on the other hand, can infect many kinds of crops.

How can I reduce future damage from Southern Blight?

I already removed the plant, including as much of the root system as I could. University of Kentucky’s information (linked previously) recommends removing the soil in that area, too, to reduce the number of reproductive bits, called Sclerotia, in the garden.

The next recommendation that organic home gardeners can follow is to grow plants that can resist Southern Blight in that area for a few years.

Resistant plants, according to University of Florida and Louisiana State University include woody plants, ornamental grasses, corn, and wheat.

The other recommendation is to raise the soil pH a bit. The fungus grows more slowly in higher-pH soils.

The good news: no evidence of root-knot nematodes

If there were root-knot nematodes adding to the damage, the roots would look lumpy. Maybe other gardeners are not as relieved as I am to see this lack of lumpiness, but some years my garden is seriously affected by the nematodes.

Where did the Southern Blight come from?

This is hard to know. My garden has never, until now, shown any sign of harboring Southern Blight. The disease can travel on infected plants, mulches, soil, and contaminated tools. I am thinking that it could also be spread by ground-scratching birds, but they are not mentioned in any of the publications I checked.

A new tomato plant growing nearby

At the end of June, when we returned from five weeks of travel and before we drove across Texas to visit family in the Austin and Houston areas, I planted two tomato seeds in the garden. Luckily, they are in a separate garden bed from the blighted plant.

I set the seeds inside a collar formed by a paper cup that had the bottom removed. The collar was to help hold moisture and to protect the seeds from being eaten. I watered the area well before we got in the car and headed west.

Amazingly, when we got back from our 8-day tour of relatives, a little tomato plant was standing where I had planted those two seeds.

I had planted some Swiss chard and a leaf-amaranth in the same little garden area, and they were coming up, too. A caterpillar of some kind found those to be delicious, so I had to replant the greens, but all is looking good now.

That little tomato plant has flowers on it today. If all goes well, there will be more garden-tomatoes coming into my kitchen by late September, and, hopefully, the potential disaster of Southern Blight will not be causing too many more problems.

Some varieties of tomato die in my yard. The most obvious sign of their impending doom is wilting. The presence of many dead leaves is another easy-to-notice sign.

When a tomato plant starts to look extra-pathetic, figuring out the cause is important. Sometimes, the plant can be saved. More often, it can’t, but knowing the cause can help the gardener prevent problems in the next-summer’s garden.

This article describes the way I figure out what is wrong with an ailing tomato plant.

Wilt versus leaf roll

Stressed plants will sometimes roll or curl their leaves. This is different from wilting. In the leaf roll response, leaves roll or curl upward at the edges. The roll can be extreme, so that each rolled leaf is almost cigar-shaped, with the lower leaf surface seen on the outside of the roll.

University of Washington’s publication on leaf roll in tomatoes explains that this sign has several possible causes, that are not diseases, including high temperatures and fluctuating soil moisture levels, and that it is more common in indeterminate plants than in determinate plants.

Wilted leaves, unlike leaves doing the leaf roll thing, do not roll inward/upward.

Wilting caused by something other than disease

Wilting in tomato plants can have non-disease causes.

Soil moisture

The obvious first thing to check when a plant looks wilted is the soil moisture level.

It makes sense to pretty much everyone that a plant might wilt in dry soil, but when soil is too wet, that can also cause wilting due to roots that have drowned and no longer work to pull water into the plant.

If you aren’t sure about the soil moisture level, poke a trowel down into the soil not too far from the wilted plant, then pull back on the handle to make an open wedge that your hand will fit into. Reach down into the soil with a bare hand to check for dampness.

Too-dry soil is one cause of wilting that a gardener can fix. Too-wet soil is less easy to fix quickly, and a drowned root system takes a long time to overcome.

Damage to the main stem

If a plant is wilted, another thing to check after soil moisture is whether the main stem is damaged.

If the main stem is very damaged, it is possible that the plant’s water-conducting tubes have been damaged, too, and can not move water well-enough through the plant.

A damaged tomato-stem cannot be fixed. If the damage is near the ground, caused by a mechanical injury (being bumped or scraped), raising up a mound of soil above the damaged area may help.

Tomato plants can make new roots on the main stem,. The mounded up soil can allow new roots to form above the damage. Growing new roots takes time, though. The tomato harvest may be slower to arrive and smaller than for a plant that didn’t have a delay.

Loss of roots due to gophers

Gophers can ruin a garden, plant by plant. They burrow underground and eat plant roots. Most of us will not ever have this problem in our gardens, but gophers were my second stepdad’s garden nemesis.

Gophers usually leave mounded trails through the garden. If a plant simply falls over one day, and you discover that its roots have disappeared, look for the trails.

A plant that has lost its roots to gophers won’t recover.

Wilting caused by diseases in the soil

The next step, if all of the above do not seem to be the cause of wilting in your tomato plant, is to dissect the plant for a closer look.

Cut across the main stem near the ground, and look inside the stem. Is the tissue a healthy greenish-white all the way across, or are there some brown areas inside the stem?

Fungus underground

The two fungal diseases that cause most of the wilting in tomato plants that I have seen in Georgia are fusarium wilt and verticillium wilt.

To be honest, I usually cannot tell which one has caused the trouble, but both will show browned areas inside the stem that are where the fungus has entered the plant through the roots and clogged up the water-conducting tubes.

These diseases cause more trouble in very wet soils.

I have grown the heirloom tomato variety ‘Mortgage Lifter’ in both wet and dry years. In dry years, the plants are productive and make delicious tomatoes through the whole season. In rainy/wet years, the plants die from one of these fungal wilt diseases by mid-July.

EDIT from 20 Aug 2019 – A new soil-borne fungus that attacks tomato plants has shown up in my garden. See my article “What Caused my Tomato Plant to Wilt, Part 2” to read about Southern Blight in my garden.

Bacterial wilt

Bacterial wilt causes rapid wilting of the whole plant. If your plant has wilted completely, seemingly overnight, this is a cause to suspect.

University of Florida’s information on bacterial wilt describes a simple stem-streaming test that you can do at home, to check for this disease:

Cut a stem from the wilted plant and suspend the cut end in clear water. White, cloudy material oozing out of the cut end into the water is a sign that the plant is infected by bacterial wilt. If nothing oozes out of the stem, then bacterial wilt is not the cause of your tomato plant’s wilting.

I have only been able to confirm bacterial wilt as a cause of tomato wilting once, in someone else’s garden, in my many years of looking at wilted tomato plants. That makes me think that this cause of wilting is not super-common.

Wilting caused by nematodes in the soil

Root-knot nematodes — microscopic wormlike creatures — are another possible cause of wilting in tomato plants. If all of the above-ground parts of the plant check out as being fine, except for the wilting, the next place to look is the root system.

Dig up the roots of the wilted plant, and examine them carefully. Healthy roots are creamy white in color, and they are fairly uniform in diameter, gradually decreasing in width as you follow them to the growing tips.

The roots of tomato plants infested by root-knot nematodes are lumpy, looking a bit like they have swallowed large beads.

The University of Arkansas publication (pdf) about root-knot nematodes includes photos of healthy and infested roots, side by side, for comparison. If your plant’s roots are lumpy, then root-knot nematodes are the likely cause of wilting.

Wilting caused by leaf diseases

All of the above causes of wilt can include some yellowing of the leaves, but not brown spots on the leaves. If a tomato plant has many wilted, yellowing and/or browned leaves, and it also has a lot of spotted leaves, then a leaf spot disease is a likely cause.

Leaf spot diseases can affect most tomato plants as the season progresses. These diseases tend to be worse in wet years than in drier years, but nearly every spring-planted tomato plant in the Southeastern US will show some signs of a leaf disease by the end of September.

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The brown spots on the leaves are an easy-to-see clue.

Cure for wilted tomato plants

Many of the causes listed above do not have an easy cure. Most of them, though, can be avoided in next-year’s garden with some planning.

If the garden soil is in a place that stays wet much of the time, raising it up a few inches can improve drainage and reduce the risk of the moisture-related wilt problems, like the soil-borne diseases.

Another simple step is to grow disease-resistant and nematode-resistant varieties. Many of these are hybrids, not heirlooms, but some heirloom varieties also survive just fine in my garden. Some will do fine in yours, too; however, finding them may take time.