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What a disaster! Months spent caring for tomato plants only to wake one morning to suddenly find a sickly-looking plant about to lose all its fruit.
Depending on how late in the season the wilting happens, it could cut your season short. Late season tomatoes could be done for unless it’s a straightforward fix.
The only easy fixes are watering problems, and even then, you still need to nip things in the bud before the roots become damaged.
Whether you’re early on in the season or your crops are ruined, you still need your question answered… Why is my tomato plant wilting?
The main reason isn’t to save this year’s harvest. It’s so that you know how to prevent a repeat of the same problem next season.
There are a handful of diseases that can cause your tomato plant to wilt. By identifying the disease, you can harvest a resistant variety next season.
The fungal and bacterial diseases that can cause wilting (and will probably kill your plant) are listed below, along with the codes to identify the resistant varieties to grow in the future.
Watering Problems that Cause Tomato Plants to Wilt
1 – Dehydration / Drought
Dehydrated tomato plants wilt in the morning. That’s natural. And it’s the right time to water them. The earlier in the day you get them watered, the more the plant will use.
By mid-afternoon when the temperature is at its hottest, much of the water you add to warm soil gets lost to evaporation. Let that happen, and it’ll be wilted the next morning too.
Sometimes, the stems droop, leaves curl, and the plant wilts to fend off sunlight. It’s a reflex to high temperatures, and a fascinating process to watch unfold.
When tomato plants get too hot, they curl and wilt as a defence mechanism.
By lowering the leaf surface that’s exposed to heat, it conserves more water in its leaves.
Pretty smart plants!
That’s why you can see them wilt in the afternoon, then perk back up later when it’s cooler.
It’s never a good idea to water tomato plants later in the day. The soil will stay moist for longer.
These plants are tough. An overnight wait won’t kill them. Watering late in the day can damage the roots and that almost always ends in a catastrophe.
Wilting in warm temperatures is just how tomato plants behave. They only need water when the soil is dry to a depth of a couple of inches at least.
Tomato plants can tolerate drought better than excess moisture. Don’t let their strange wilting behavior in the afternoons trick you into watering them. Wait until the morning.
2 – Overwatering / Compacted Soil
Overwatering is wasting water. It’s essentially just leaching the soil.
You’ll run your water bill up, and you’ll go through more fertilizer than you need to because runoff water washes nutrients away. The roots don’t soak up what they could.
When a tomato plant has wet feet from sitting in soggy soil, it wilts first. The leaves will still be green.
If you see healthy-looking lush green leaves on tomato plants begin to wilt, hold back on watering. It’ll be the existing excess of moisture that’s stressing it.
Adding more water to an already saturated soil bed will suffocate the roots, cutting off its oxygen supply. Then you’ll be left with yellow leaves on wilting stems.
There is a fine balancing act to strike for how often to water tomatoes. The frequency of watering will be based on the depth of the roots. Most tomato plants’ roots are within the top 12 to 18 inches of soil.
If you aerate the soil before transplanting, it should encourage roots to grow deeper. If the soil is compact though, they’ll spread closer to the topsoil.
A tomato plant with shallow roots near the topsoil will need more frequent watering.
Watch for signs of stress from over-hydrating tomato plants. It’s so easy to add to the problem you’re trying to fix.
The best practice before transplanting is to aerate the soil, transplant the tomato plants, then deep water to encourage downward root growth. Drip irrigation watering systems are terrific at encouraging deep root growth.
The deeper the rooting system, the more moisture the roots will absorb.
Let this season’s tomato wilting be a lesson.
Next season, dig deeper. Start with a 12” hole, shovel in a heap of compost, then backfill with sandy loam soil for speedy drainage.
Diseases That Cause Tomato Plants to Wilt
1 – Verticillium wilt and Fusarium wilt
These are two very similar fungal infections that originate in the soil. Tomatoes aren’t their only host plant though.
These two diseases are the reason for crop rotation. Regardless of the size of your planting bed.
It only takes one contaminated seed or transplant to render your soil useless to any plant in the Solanaceae (nightshade) family.
Other host plants in the same family are potato plants, eggplants, petunias, peppers, sweet chili, jalapeño, and bittersweet.
Fusarium wilt is the more common of the two. It can lay dormant in the soil for years, activating when the soil temperature climbs above 75oF (approx. 28oC).
Wilting in midsummer is when to be on guard with this. The fungus starts in the soil, enters the roots, spreading up through the stem, blocking vessels along the way.
Once water and nutrients can’t travel through the vessels, quick to follow are yellow leaves on tomato plants.
The yellowing can start on one side of the plant only. That’s because it might only start with one of the roots being affected or one side of the root system. It is contagious though.
This rots the plant from the bottom up. It is effectively root rot, but the cause is the fungal pathogen in the soil. Not from overwatering, or using infected tools that have spread fungal spores to the plant.
There are ways to save a dying plant from root rot, but not when it’s caused by these fungal pathogens.
Speaking of tools, if you do suspect fusarium or verticillium to be the cause of your tomato plant wilting, everything needs to be sterilized.
Two effective ways to sterilize your gardening tools (without corroding metal by using bleach) are to use either rubbing alcohol (isopropyl 70%) or hydrogen peroxide (3%).
Verticillium wilt is very similar to fusarium wilt, but it doesn’t reach the top leaves. It will kill all the lower mature leaves and those will drop.
When fusarium wilt is the issue, dead leaves don’t drop. They cling to the plant, even after it has killed it.
Verticillium wilt can activate at lower soil temperatures above 55oF. If you notice wilting and yellow leaves from the bottom up in early spring, that’s when to suspect this.
For confirmation of either fungus, cut the stem off the plant and make a horizontal cut to open it. The veins inside the stem that should be transporting nutrients to the leaves, will instead be thin brown columns.
If you do identify either of these pathogens in your soil, the soil is redundant. It will return year after year on any host plant.
2 – Tomato Spotted Wilt Virus (TSWV)
With a name like Tomato Spotted Wilt Virus, you’d think it’d be easy to identify. Spots on a wilting tomato plant, surely, it’s TMSV?
Not so. The signs are similar to other fungal diseases, namely Verticillium wilt and Fusarium wilt.
It is a soil-borne fungus infection but that is not how it starts. TSWV is spread by thrips. There’s nine species of them.
To date, 174 different plant species have been identified as host plants.
TSWV can only be spread by thrips so managing those pests is the only way to prevent it.
How to Control Thrips
- Yellow sticky cards
- A magnifying glass
- An internet connection to do Google image searches for various species of thrips. The three most common are western flower thrips, tobacco thrips, and onion thrips.
For the yellow sticky cards, according to Michigan State University, ten thrips per card is a low population. But they can’t say how many thrips it would take to, well, rip right through a greenhouse destroying all the crops.
The western flower thrip typically feeds on the fruit of a plant, whereas tobacco thrips feed on the foliage.
Insecticide control is a double-edged sword with these. For example, insecticides that contain imidacloprid, which is a neurotoxin for tobacco thrips don’t affect the western flower thrips the same. It does the opposite and entices them to feed more.
3 – Bacterial Wilt
Bacterial wilt is brutal on tomato plants. It can kill plants before chlorosis sets in. It causes sudden severe wilting of the stems from the top down, yet the leaves on those stems can remain green.
It’s caused by the Ralstonia solanacearum pathogen, and similar to other common tomato diseases, all plants in the solanaceous family are susceptible to it. Once it’s in the vascular tissue, it can clog fast.
It thrives in moist hot soil. Yet another reason to take care with the watering.
Similar to the pathogens of Verticillium and Fusarium, this clogs the vascular tissue in the plant’s stem, preventing water from travelling further up the stem.
In laymen’s terms, bacterial wilt causes plants to wilt from the top down.
But they can look like they’re recovering at night. That’s only because they don’t need to try to hydrate from the roots. They stop wilting when there’s enough water storage in the leaves.
Once the temperatures rise, they’ll try to drink from the bottom up, but because of the clogging in the stems, they won’t be able to get a drink.
That’s why it wilts by day, then perks up at night. Until it’s run dry completely, at which point, it decays and dies.
The difference in diagnosing bacterial wilt is that when you cut into the stem it won’t necessarily be brown.
If you suspect that Ralstonia solanacearum bacterium is present, take a cutting, place it in the clear glass jar of water and watch for a cloud of white milky-looking sap oozing from the cut section of stem.
Here’s a video on YouTube showing what bacterial wilt on a tomato plant cutting looks like…
4 – Tomato Pith Necrosis
Although a rarer disease, it is still among the list of diseases that cause tomato plants to wilt. This is a bacterial infection caused by the Pseudomonas corrugata pathogen.
It’s more prevalent in the early season when temperatures are cooler and the weather is wet. Particularly in early spring when tomatoes are entering their fast growth stage.
Applying fertilizer in conditions that favor the pathogen will speed up its spread. Avoid fertilizing in early spring when temperatures are cooler and there’s still a wet period ahead. Wait for drier days.
Any wounds on the roots, the stem, or openings near the base of the plant are entry points for diseases.
Symptoms of tomato pith necrosis include brown lesions on the stem, and side shoots can have blackening edges on the leaves.
Chlorosis happens on the lower leaves, and there are usually brown necrotic lesions on the stem with wilting happening above the necrotic spots.
The stem damage at the base of the plant cuts the water supply off to the upper part. That’s why the lower portion of the stem turns necrotic first but the top of the plant wilts.
Eventually, the inside of the stem turns hollow and depending on the size of the plant, the weight could cause the stem to snap resulting in the tomato plant toppling over.
The Most Notorious Tomato Plant Pest
This is a minuscule worm that lives in the soil, slowly munching away on the roots. In fact, “tiny” isn’t even the right word. They’re so small they’re invisible to the naked eye.
These are parasitic nematodes that only feed on live plant matter, never going above the soil line to feed on the foliage like other types of nematodes would.
The root-knot nematode will feast on the roots only. All you’ll see is a dreadfully looking unhealthy plant. Droopy stems, wilting leaves, discoloration, and fast deterioration.
Worst case scenario, the entry holes in the roots they make when feeding become an entryway for any of the bacterial or fungal diseases above.
Best case, you catch the wilting early, inspect the roots, and spot the beady appearance of swollen roots that confirm a nematode presence.
If you do identify these as the parasite that’s eating your tomato plants’ roots, destroy the plant and quarantine the area. Leave them long enough with no plant tissue to feed on, they’ll die off.
Disease Resistant Varieties of Tomatoes Plants
Whenever you identify wilting on tomato plants, it’s imperative to identify the cause. Especially if it’s been a disease because if it’s in the soil, the same problem will return.
Not just on tomato plants but any plant in the nightshade family. That takes 90 groups of plants off the table. Among those are 3,000 species. Many of them are edible.
Diseases on tomato plants are so common that they’ve been given special codes. They’re shown on the labels on seed mix packets, or in the description if you’re ordering from an online nursery.
- V = Resistant to Verticulium Wilt
- F = Resistant to Fusurium wilt
- N = Nematode resistant
- T = Resistant to Tobacco Mosaic Virus
- A = Resistant to Alternaria Leaf Spot
- St = Resistant to Gray Leaf Spot (St is the abbreviation for Stemphylium – the fungus that causes gray leaf spot)
Next season, start with new seeds and not seeds you’ve harvested from a bad batch. This time, look at the labels on the seed mix packets and go with one that is cultivated to be resistant to the disease you’ve had problems with before.
Keep in mind, resistance isn’t the same as immune. It just means that if they do get infected, they’re better equipped to fight off the disease.