Control tomato fungus

Controlling tomato fungus is a common challenge that tomato growers must face. If a tomato plant becomes infected with tomato fungus, it may be overrun very quickly. If infected with a fungus, a tomato plant may show several symptoms: The leaves may shrivel up and crumble, or turn yellow, or even become covered in black spots and fuzzy white mold.

Fungal diseases can kill the plant and quickly spread to other tomato plants. If a fungus problem is affecting your tomato plants it is important to take action quickly to bring it under control. If not, there are still many steps that you can take to prevent tomato fungus diseases from occurring.

This article lists many different tomato fungus varieties, with pictures of each one to help you to identify them. It also contains many tips for preventing fungus diseases on tomatoes, as well as advice on using fungicides to control a tomato fungus problem.

Control tomato fungus – tomato fungus types

Tomato fungus problems can be caused by several fungal leaf or fruit diseases or blights. The most common is known as Septoria leaf spot.

Septoria Leaf Spot

Septoria leaf spot usually appears on tomato leaves after the first fruits set. The fungus typically affects the lower leaves first. Septoria can be identified by small grey spots with black centers. These spots are usually confined to the leaves, but can also appear on the vines. Septoria leaf spot on tomatoes can cause the affected leaves to turn yellow and eventually fall off. Leaf drop reduces the fruit production of the tomato plant.

An additional side effect on a tomato plant shedding its leaves is that the fruits have less shade from the sun, allowing sun-scald. Tomato Septoria enjoys cool, rainy or humid weather conditions.

Septoria Leaf Spot

A tomato leaf showing Septoria Leaf Spot - notice the green leaf beginning to yellow around the spots

Early Blight

Early blight on tomatoes is one of the most common tomato growing problems faced by vegetable gardeners. Early Blight causes a few large spots to appear on each affected leaf. The spots look like several rings inside each other – like the rings of a tree. Eventually the leaf will turn yellow and drop.

Like Septoria Leaf Spot, Early Blight begins on the lower leaves. Under cool, moist conditions it will spread upwards, causing many leaves to drop. Early Blight on tomatoes can also affect the fruit, creating large dark rings or spots. Tomatoes with early blight spots will drop before they are fully grown.

Early Blight problems are typically going to affect tomato plants early-on in the season. Other plants are susceptible to early blight, including aubergines and potatoes.

tomato leaf early blight

Notice the concentric rings, a sign of early blight on this tomato leaf

Late Blight

Late Blight Tomato

A tomato with a large spot caused by late blight fungus

Late Blight Tomato Leaf

A tomato leaf showing signs of a late blight fungus problem

If the climate in your area is typified by cool, wet, humid nights and warm days, then tomatoes planted in your vegetable garden will be susceptible to Late Blight. Late Blight causes green/black areas at the outer edges of leaves.

Late Blight Spots have a shiny/wet appearance. You may also notice a white fuzzy mold growing in the spots. Late Blight can affect the fruit, creating green spots which quickly turn brown and hard.

Late Blight is one of the most serious tomato fungus diseases – it can spread extremely rapidly and will kill a plant if it is not dealt with.

Southern Blight (Stem Rot)

Southern Blight can be identified quite easily. Near the soil, there will be white furry mold growing on the stem of the plant. Following this, dark spots will appear on the lower portion of the stem. Southern Blight will hinder plants from drawing up nutrients and water from their roots. This may result in the plants toppling over or completely wilting.

Southern Blight Stem Rot

Southern blight mold girdling the stems of a tomato plant

Powdery Mildew

This is another fungal tomato disease. Powdery Mildew is very easy to identify. It appears on the top of tomato leaves as white powdery spots. Sometime the spots will be yellowish, but still powdery. Powdery mildew is not usually a fatal disease to tomato plants, but it will weaken them and lower the quality of the fruit. Like all other tomato fungus problems, it thrives in damp, moist and humid conditions, crowded vegetable gardens and where the air circulation is restricted.

A severe mildew problem will make affected leaves leaves turn yellow and then brown and crusty. If the leaves drop, it may result in sun damage to the tomatoes and will result in a lower tomato yield.

The powdery mildew fungus is also spread by insect pests (thrips, psyllids, aphids and whiteflies). (Learn more about tomato pests)

Powdery mildew fungus thrives in conditions where the weather is humid during the night (higher then 85%) and then warm and dry during the day.

Powdery Mildew

White powdery mildew tomato fungus problem

Blossom End Rot

A common fungus that affects the tomato fruit. Dark spots can appear at the blossom end of the tomato (the bottom). The spots enlarge while the tomato starts to rot. Blossom end rot is often worsened by a lack of calcium in the fertilizer.

Blossom End Rot

The blossom end rot problem on this tomato is quite advanced

Anthracnose

Anthracnose is a fungus that affects the tomato fruit. The first sign of Anthracnose is a small dark pit appearing on the fruit, which becomes larger and darker and is often joined by further pits. This fungus is commonly picked up from the soil, either by splashing soil on the plant during watering, or from tomatoes that are resting on the ground. It affects both green and red fruit. Often several pits will merge into one large rotten area. The fungus spores can survive the winter cold.

Tomato Anthracnose

Small pits in tomato caused by anthracnose fungus

Control tomato fungus – causes of fungus

Tomato fungus diseases are worsened by certain conditions. Fungus loves moisture and cool conditions, so the weather and environment are a big factor in the susceptibility of your garden to tomato fungus problems. Rain, dew and other sources of moisture – especially close to the ground – encourages fungus to grow.


Lack of ventilation will also make fungus problems worse. Watering and garden maintenance can spread fungus spores from plant to plant. However, there are actions that can be taken to prevent tomato fungus developing and spreading.

Control tomato fungus – how to prevent fungus

  • Many fungus / blight spores can survive the winter. So it is important that you don’t compost dead leaves or plants. Any fungus affected leaves, vines and fruit should be thrown away in the fall.
  • Watering your tomato plants from above will spread the fungus spores from diseased plants to surrounding plants. So, make sure that you water closer to the ground, but take care to avoid splashing soil up onto the stems. Gentle, careful watering is key. Be careful when working in and around your tomatoes. If you knock them or brush against them, you can accidentally disperse fungus spores to nearby plants.
  • If diseased leaves or fruit fall from your tomato plant, you should gather these up and dispose of them as soon as possible. If you do not, the fungus spores may lie dormant in the soil over the winter.
  • To aid ventilation, you should trim the bottom 25% of your tomato plant of all vines and leaves. This will increase airflow and decrease humidity around the base of the plant and in the soil.
  • Growing any crop in the same location for year increases the possibility of disease problems. The possibility of fungus problems will be reduced by using crop rotation – particularly recommended if your tomatoes have had Southern Blight. By rotating your crops, you should be able to avoid planting them in the same location for a few years.
  • Staking (growing on tomato cages/frames) is key to controlling early blight and southern blight, since it keeps the foliage and fruit away from the soil. Having your plant trailing on the ground is just asking for blight, as the blight fungi are usually present in soil.
  • Avoid high nitrogen fertilizers. High-nitrogen nutrients in your fertilizer can encourage leaf fungus in tomatoes. Nitrogen causes the plant to develop many leaves. This thick foliage reduces air circulation.  Tomatoes prefer high phosphorus and calcium fertilizers.
  • Avoid crowding your tomato plants – crowding too many plants into an area allows leaves to stay wet, ideal for fungus growth.
  • Buy tomato plant varieties or seed that are marked as disease resistant.

Control tomato fungus – fungicides

If you need an immediate solution to a tomato fungus problem, you should use various organic fungicides to control them. If your plants have suffered from fungus or blight in the past, or you live in a cool rainy climate, it is a good idea to start a spraying program before any sign of disease appears. The best time to start spraying your tomatoes is early to mid July. At this time the first pea-sized tomatoes should just have started to appear. Apply the fungicidal spray to your tomatoes at 7 to 10-day intervals for the whole season, and after rainfall.

Copper and sulfur based fungicides can be used in organic gardens. A popular commercial organic fungicide is Kocide 101, which is used for control of Septoria Leaf Spot and Early Blight. Other Organic Fungicides that you can use are Serenade and Messenger, which boosts the crop’s inbuilt defenses. Cornmeal solution used to drench the soil around the base of young plants has also been found effective at controlling all types of tomato blight.

If you are not strictly into organic growing, you can get many effective chemical fungicides at your garden center. Ask for fungicides based on Chlorothanolil, Maneb, or Mancozeb (I needed to write them down as I can never remember them ;) ) These will be stocked under a variety of trade names, such as Daconil and Serenade. Actinovate is another popular fungicide, for use on new seedlings. Fungicides should be sprayed every 1-2 weeks. Always follow the instructions for the correct waiting period before harvesting your crops.

 

Every gardener will have to control tomato fungus at some point. Fungus is one of the most common tomatoes diseases. The different types of tomato fungus problems we have examined here can all be prevented by using several common techniques. Tomato fungus is not difficult to control, as long as you prepare your garden, plan ahead and know what to expect. I hope the information in this article will help you to do just that! Good luck, and keep fighting those tomatoes diseases!