Tomato Diseases and Prevention

The Tasteful Garden promotes natural disease control methods such as keeping your garden clean and weeded, using mulches and good compost in the soil, and using only organically made sprays and pesticides when absolutely necessary.

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Diseases can be heartbreaking when they happen as for many of the diseases we mention here, the only treatment is to pull the entire plant out to save the rest of your garden. Prevention is the best cure and in many cases, there just is nothing that can be done at all to avoid losing one or two plants to disease.

Below we have listed some of the more common diseases for gardeners to be aware of. Also note that many diseases are spread by splashing water so water sprinklers and heavy rains can create molds, fungus’, and bacterial diseases which can make your plants very unhappy and sometimes can kill them. Mulching with dried leaves, pine straw, hay straw, grass clippings, newspaper, and even cardboard can make all the difference in keeping diseases under control. They can also help hold in moisture and protect from overheating the soil in the hot summer months. This keeps plants happier and healthier and can prevent stressful conditions which invite diseases. Cool, wet weather is the number one cause of fungal growth. Spacing your plants so that the leaves can dry quickly after a rainfall will help prevent extremely moist conditions.

There are also many living creatures in the soil which help to break it down and provide nutritious soil for your plants such as earthworms and good bacteria that can, over time, remove soil borne diseases. If you have had problems with soil borne diseases, move your tomatoes and peppers to the other side of the garden and add worm castings and good compost to that area to rejuvenate for a year or two.

Plant Problems (Not diseases, but things you need to know about)

Blossom End Rot is a so called “disease” that is caused by soil conditions. If there is problems with the plant taking up calcium, either from too wet soil, wet/dry soil frequency, pH issues or just not enough calcium in the soil, you can get Blossom End Rot. Click here to read more.

Fertilizer deficiency will show up in many ways on tomato plants but generally a overall yellowing of the plant means that there is a lack of nitrogen and possibly other nutrients. A good general purpose vegetable fertilizer (preferably organic type) will solve most if not all nutrition problems. A quick feeding can be done with liquid fertilizers such as ones that are made from Kelp or fish meal, or compost tea made from rich compost or worm castings.

Over or Under Watering is of course not a disease but can cause lots of problems in the garden. When plants have watering stress, they are more likely to develop other diseases and may even die from drowning. Roots must have air, moisture (not too much), and nutrition just like we do so think about what you would like if you were a tomato plant and try to provide that. Drip watering can keep the soil moist and cool and is much better than having their leaves soaking wet.

Blossom Drop is when the flowers of the tomato seem to just rot off or fall off spontaneously. This is generally caused by temperatures being too cold or too hot for the fruit to actually set or pollinate. If flowers are not pollinated, they dry up and drop off without creating a tomato. Ideal temperatures for tomato set are above 55 at night, below 85 during the day, and below 71 degrees at night.

Soil Borne diseases:

(For soil borne diseases, there is some evidence that super heating the soil during the hottest 2 months of the summer, with black plastic laid down on the top of the soil, will kill soil fungi. You should move the location of your tomatoes and peppers to prevent re-occurrence next year.)

Verticillium Wilt


Verticillium wilt is a soil-borne fungal disease that results in the yellowing, and eventual browning and death of leaves and stems, particularly in branches closest to the soil. The wilt starts as yellow, V-shaped areas on the leaves. These yellow areas grow over time, turn brown, and then the leaf dies. Often, entire branches are infected and eventually the whole plant may die.

Damage to Plants:

Despite the sickly appearance of verticillium wilt-infected branches, often the upper part of the plant will continue growing, though growth will be stunted. Tomatoes that are growing on infected branches will often drop before reaching maturity, or they will be sunburned because of the lack of shade that the foliage would have provided. Even on branches that are not showing signs of wilt, the tomatoes will be smaller than normal, and often develop yellow shoulders.

Life Cycle:

Verticillium wilt is the result of a fungus called Verticillium albo-atrum, and is present in most soils which tend to be cool for long periods of time. It stays alive season after season by living on the dying underground parts of infected plants. It often attacks, and multiplies, on the roots of common weeds such as ragweed and cocklebur.

Treatment and Prevention:

Once you notice signs of wilt on your plants, there’s really nothing you can do to prevent further damage during the current growing season. There are two things to do to ensure crop health in the upcoming gardening season. First, don’t plant tomatoes in the same spot for at least three years. This will allow the fungus in the soil to reduce enough (without tomato roots or other Solanaecae family members to feed on) to make it safe to grow there again. Also, if Verticillium wilt has been a recurring problem in your garden, look for hybrid varieties that are wilt resistant. These will be labelled with a “V” somewhere on the plant tag or seed packet, near the variety name. (Most of our hybrids have verticillium resistance)

Fusarium wilt

Fusarium wilt is a disease caused by a fungus, Fusarium oxysporum f. sp. Lycopersici, which lives in the soil. It is often confused with verticillium wilt because both produce similar symptoms in tomatoes.

The fungus works its way up through the plant’s roots, clogging water-conducting tissue in the stem. That prevents water from reaching branches and leaves, starving the plant. Affected plants produce very few tomatoes. Often, the entire plant dies.

What does fusarium wilt look like?

The first signs are yellowing and wilting on one side of the plant on a leaf, single shoot, branch, or several branches. Yellowing and wilting move up the plant as the fungus spreads and wilted leaves dry and drop prematurely. The interior of main stem (when split) shows discolored streaks from plugged water-conducting tissues. If the plant doesn’t die completely, it will be weak and produce inferior tomatoes

When does fusarium wilt affect plants?

The disease can attack at any stage in a tomato plant’s growth, but symptoms are most common right after tomato blossoms appear. The fungus favors temperatures between 70-90 degrees Farenheit and wet weather, which allows it to spread more easily. Plants in poorly drained soil are more susceptible to infection than those in well-drained soil. Wet soil allows the fungus to multiply and move up through the tomato plant’s water-conducting tissue.

Treatment and Prevention:

Once you notice signs of wilt on your plants, there is really nothing you can do to prevent further damage during the current growing season. As with Verticillium wilt, it is necessary to move your plants to a new location, try to kill the fungus underground and then you can move them back to that location.

Fungal Airborne diseases:

Septoria Leaf Spot

Caused by the fungus Septoria lycopersici, it can be very destructive in the later stages. The disease begins when fungal spores are spread from other plants, tools, or insects. Plants are most open for infection when temperatures are moderate and moisture is abundant. It is sometimes mistaken for Early Blight.

How to Identify Septoria Leaf Spot

Leaf spot symptoms are first seen on lower leaves especially after the first fruit sets and spots may also appear on stems but rarely on fruit. These spots may appear as tan with a darker brown border with a small yellow border visible around each spot. Spots can merge until the leaf shrivels up and severe cases can cause the leaves to turn yellow, brown, then wither.


The disease is worsened by moderate temperatures (68 to 77 degrees farenheit) and abundant rainfall, is easily spread by splashing water, and the fungus survives between seasons on infected plant debris. Extended periods of leaf wetness, high humidity, and warm temperatures exacerbate the development and spread of the disease.


Fungicides are very effective in control of septoria leaf spot; copper, chlorothalonil, and mancozeb fungicides are available for homeowner use. Use fungicide in combination with as many preventative methods as possible to be most effective.

Early Blight


Early blight of tomatoes is one of the most severe tomato diseases affecting home gardeners which can affect the stems, leaves, and fruit of tomato plants. It can also cause damping-off in seedlings. It does not usually occur in arid, dry regions but is most active in warm, wet or rainy conditions. Caused by the fungus called Alternaria solani which is most severe on plants stressed by a heavy load of fruit or low nitrogen fertility it is generally worse during the rainy season. Brown circular “bull’s eye” rings appear as 1/2-inch diameter leaf spots, first on lower, older leaves. As the disease progresses, stems and fruit may become infected. Leaves turn yellow and wither, starting at the base of the plant, until the whole plant is affected.

Causes of Early Blight

The fungus survives in infested soil and plant residue. Therefore, planting successive years in the same soil can cause a recurrence of the disease. It is caused by different fungi than late blight. The spores can be spread by wind, water, insects, humans, and tools and when they land on plants, they will affect the leaves mostly when they are wet.


A combination of practices can help keep the fungus under control. The best method is prevention. Once it’s started the disease is very difficult to control, even with fungicides. Increase the amount of organic matter in the soil, good compost will increase fertility and decrease nematodes.

When early symptoms of the fungus are detected, apply protectant fungicides (carbamates, clorotalonil, and cuprics) to the entire plant using in intervals of seven days if the conditions are wet or ten days if the weather is dry. Rain or overhead irrigation will wash off the fungicide treatments so fungicide will have to be reapplied.

Late Blight

Late Blight caused by Phytopthora infestans is the most severe disease of both potatoes and tomatoes. While it is rare for it to show up, it spreads easily on wind and rain and is capable of destroying entire fields in a few days. Late blight is extremely destructive when not managed, quickly killing foliage and infecting fruit and tubers. It does not live over in the soil but travels in the air very quickly which is why it is so devastating.


The most common symptoms on tomatoes are sunken, dark green or brown lesions on leaves and brown lesions on stems, with white fungal growth developing under moist conditions. Classic symptoms are large (at least nickel-sized) olive-green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain). Sometimes the lesion border is yellow or has a water-soaked appearance. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit.


Best to quickly destroy the plants without disturbing the spores of the fungal growth. Throw a large bag over your plants before you attempt to remove them and wash everything they could have had contact with in a mild Clorox solution.

Diseases fungal and bacterial
 Click to read more about these diseases

Verticillium Wilt
Fusarium Wilt
Septoria Leaf Spot
Early Blight
Late Blight

Environmental problems
Click to read more 

Blossom End Rot
Blossom Drop
Fertilizer deficiency
Over/Under Watering

Identifying Septoria, Early Blight, Leaf Roll and Powdery Mildew (courtesy of

Identifying Late Blight (courtesy of