9 common tomato diseases to watch out for this season

Blossom-end rot

Blossom end rot is actually a nutrient deficiency disease caused by a lack of calcium. It is among the more common tomato diseases.

It attacks the fruit creating a soft dark mushy region on the lower part of the fruit away from the stalk. This region is the blossom-end of the fruit. The region gets bigger as the fruit grows and the rotting increases making it a hotspot for other bacteria and fungi to grow.

The lack of calcium can be a result of low calcium levels in the soil or a lack of sufficient water to absorb the calcium.

In such cases, increasing irrigation intervals and water amounts will help undo blossom-end rot. Another method will be to spray the plant with calcium-rich foliar fertilizers on the leaves. You can apply calcium-rich fertilizers in the soil but make sure you apply a lot of water afterward.

Read More: How to treat blossom end rot in tomatoes (black rot at the base of the fruit)

Flower and blossom drop

This condition is usually brought about by a lack of boron or a rise in temperatures above 85o F or dropping below 58o F.

You will see the young tomato blossoms dry up and fall or cling to the bud in some cases during such extreme temperatures. You know that you are losing blossoms when you see many flowers laying on the ground. However, sometimes this may go unnoticed.

It might get hot during the day but there’s little you can do about it. All you can do is keep the plants healthy and wait out the hot weather.

However, you can do something with the low night temperatures. Grow your tomatoes in a tunnel to raise the temperatures at night.

Read More: 6 Reasons why your tomato flowers are falling from the plant? (Blossom drop)


As the name suggests, it is caused by the fungus called Colletotrichum.

You will see tiny, circular, sloping areas on tomato fruits that will form rings around them. When it gets too ripe fruits, some of the fruits will rot. My advice will be to

It mainly affects the fruits and the fungi spread best when the weather is warm and wet. Splashes of water easily spread the spores from the soil and from other leaves.

Septoria leaf spot

This is a common tomato disease caused by a fungus called Septoria.

You will see circular spots on tomato leaves with dark edges and a grayish center. That is how you know your babies might be suffering from Septoria leaf spot.

In advanced cases, you will see tiny black spots appear at the center of the greyish portion of the spot. The leaves also turn yellow to brown. After which, they dry and fall off.

Eventually, the tomato plants die because they are unable to make their own food through photosynthesis. Unless, of course, you intervene in good time!

Too much moisture or wetness on the leaves, from rain and overhead irrigation, provides a perfect environment for the growth and multiplication of the fungus that causes leaf spots. Together with warm summer-like weather, they are a recipe for disaster.

Therefore, you should point your hose at the base of the tomato plant when irrigating and prop up the plant so that it is not in contact with the soil. Splashing water coupled with the wind also plays a key role in spreading tomato diseases faster.

Read More: Septoria Leaf Spot Disease

Early blight

This is a huge problem caused by spores from a fungus called Alternaria. You will most commonly see it when the tomato plant begins to set fruit. The spores occur in the air and get activated when the conditions are right.

Although you can observe it on seedlings, it is most common on plants with weak vigor (not well nourished).

It attacks the lower leaves of the tomato plant. You will know its presence by the brown and black sots appearing on the leaves (a rusty appearance). They grow to become large, misshapen spots with dark edges.

The stem side of the fruit can also get attacked and you will see large, concentric rings in this case which are sunken.

Signs and Symptoms
Leaves Stem Fruits
Older leaves Any age Any stage at maturity
Round, brown, and can grow up to half-inch in diameter. Infection may strangle the stem and cause the seedling to wilt and die Pots are leathery and black, with raised concentric ridges
Larger spots have target-like concentric rings The infected  stem turns brown, sunken, and dry They usually occur near the stem part
Tissue around spots often turns yellow On older plants, oval to irregular, dry brown areas with dark brown concentric rings. The affected fruit may fall off the plant
Severely infected leaves turn brown and fall off or cling to the stem Affects any part above the soil level  

Read More: How To Identify And Treat Early Blight Symptoms

Late blight

This disease spreads quickly and is a menace for tomato growers worldwide. It is brought about by a fungus called Phytophthora infestans.

Late blight in tomatoes is mostly prevalent in rainy conditions and especially towards the end of the planting seasons when the plants are close to stopping production.

You will see green-black splotches that may resemble frost or extreme cold damage on the leaves. Ideal weather is humid and wet with temperatures ranging 60o to 70o Fahrenheit.


Signs and Symptoms

Leaves Stem Fruits
Large, dark brown blotches with a green-gray edge can cross over major leaf vein Firm dark brown regions that present rounded edges Firm circular spots that are dark brown in color. Spots may turn soft and mushy  and are hotspots for other bacteria to enter
When very humid, thin powdery fungal growth appears When very humid, thin powdery fungal growth appears When very humid, thin powdery fungal growth appears
Progresses to leaflets and petioles   May cover large parts of the fruit

Read More: How to identify late tomato blight in the farm

Mosaic Virus

The mosaic virus is not unique to tomatoes but is a key disease. It gets into the tomato plant through cuts and bruises on the stem and leaves mostly sustained from handling the plant.

Its name comes from the mosaic-like markings, of yellow and green, that appear on the leaf upon infection. The fruits of infected plants also mottle.

Although the effects will not destroy your entire field, they will reduce the yield significantly. Some of the leaves will end up misshapen and looking like ferns.

To reduce the risk of mosaic virus infection, you should minimize handling your crops unless it is truly necessary and in that case, measures should be undertaken to make sure it is safe.

Smokers are a risk when it comes to the transmission of this virus. Leaf mosaic virus affects tobacco plants too and may be carried in cigarettes. People who smoke should avoid handling tomato plants unless they are properly sanitized and wearing garden gloves.

Fusarium and Verticillium wilt

Wilt is caused by Fusarium and Verticillium fungi found in the soil.

You will see wilting in the top or lower leaves. They will lose color and die backward towards the stalk until the whole plant succumbs.

They get into the roots of young tomato plants as they begin to establish. Once in the plant, the fungi move into the stem and begin clogging up the stem blocking the movement of food and water.

Water helps plants stay upright and firm. When the sun is hot out, your tomatoes will begin to wilt when infected by the disease. Because of the low demand for these resources at night, the crops may seem to recover when it gets dark.

If you witness any Fusarium or Verticillium wilting, do not plant tomatoes in that area or any plant from that family-like eggplant, potato, and pepper for about 5 to 6 years. The long period will give ample time for the spores to die because they have no host. The fungal spores can survive long periods without a host.

You should also consider growing tomato varieties known to have resistance against the fungi.


It is caused by fungi. They could be Pythium, Rhizoctonia, or Phytophthora.

This is a disease that affects young seedlings and seeds in the nursery. You will notice that your seeds fail to emerge above the soil while others emerge but collapse at the base of the stem and die. If you pull them up, you will see the remnants of roots are disheveled and shriveled.

Damping-off is most common in soil cold soils with poor drainage which results in very wet soils.

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