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.
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?
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 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.
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.