Tomato Diseases and Pests: Identification, Prevention, and Control

8 min readMar 29, 2021

Given proper conditions and maintenance, tomatoes are relatively easy to grow. However, they are not free from problems. As prevention is the best medicine, it is best to understand the most common pests and disease problems that could turn your highly productive farm into a sterile one.

Naturally, your location, cultural methods, and environmental conditions will affect the degree of pest infestations and disease infections on your farm. Our goal is to help you grow healthier tomatoes.

Tomato Diseases

Tomato diseases are grouped into foliar diseases, soil-borne diseases, seed-borne diseases, stem diseases, and tomato viruses. Many tomato issues resemble each other, so you may need an expert eye to identify which organism is responsible for your disease problem.

Foliar diseases

Tomato foliar diseases appear on the leaves. Fungi are major causal organisms of foliar diseases. High humidity, lack of adequate air circulation, and elevated temperatures are environmental factors that encourage the spread.

Common foliar diseases include;

Early blight (Alternaria tomatophila and A. solani)

Plant with early blight usually develops a dark spot increasing in size, forming a yellow halo-like ring resembling a bull’s eye target. They first appear on the older leaves before extending to the upper leaves, stem, and fruits. As the disease continues, leaves die as a result of severe blight — lowering the overall yield.

Late blight (Phytophthora infestans)

Due to the widespread, the late blight disease has the potential of having exceedingly destructive impacts on your farm. The fungus can affect all plant parts beginning with a small dark progressive legion which enlarges into a white mould at the margin. Complete defoliation occurs within 14 days of the first symptom, and the fruit later develops thick and sunken dark-coloured lesions.

Powdery mildew (Oidium neolycopersici and Leveillula taurica)

The most visible signs of this disease are circular collections of white powdery fungal spores. The infection begins with a pale yellow spot on the leaves. As the disease progresses, the whitish part becomes brown, dry, and brittle. Infections spread rapidly, resulting in the death of infected plants.

Soil Borne diseases

Soil-borne diseases occur in areas that have grown tomatoes over a long time, leaving residues of disease-causing organisms. The infection leads to limited water supply and nutrient transport.

Common soil-borne diseases include;

Bacterial wilt (Ralstonia solanacearum)

Bacterial wilt is the most crucial tomato disease in most parts of the world, including Nigeria. Infection occurs mainly during high temperatures and moisture. The bacterium multiplies inside the xylem (water-conducting tissue of the plant), filling the tissue with slime. This results in rapid wilting and desiccation occurrence, leading to plant death.

Corky root rot (Pyrenochaeta lycopersici)

Roots of infected plants take on a corky texture while smaller roots rot or decay. Plants infected with corky root rot are often small and less vigorous, which leads to a reduction of nutrient uptake to the plant.

Fusarium wilt (Fusarium oxysporum f. sp. lycopersici)

The fungus passes upward from the roots into the water-conducting system of the stem; Preventing both the water and food conducting vessels. It disrupts the flow of nutrients, leading to wilting, yellowing, and eventual leaf loss.

Seed borne diseases

Seedborne diseases develop through untreated seeds. They can be managed using preventive seed treatment practices. Obtaining seeds varieties from reputable seed vendors can prevent seed-borne diseases.

Here are common seed-borne diseases;

Bacterial spot (Xanthomonas spp.)

The infection begins as a small water-soaked spot. Lesions then progress into necrotic areas leaving the leaves to turn yellow and shed. The lesion starts as a slight blister which advances into lesions with a slightly raised margin and hollow centre, giving the fruit an unpleasant appearance.

Bacterial canker (Clavibacter michiganensis subsp. michiganensis)

Bacterial canker is a common and destructive disease. Infections can attack tomato plants of any age, often leading to death. Symptoms may begin with white leaf spots, showing wilting while the spotted area on the fruit develops a raised dark centre often referred to as “Bird’s Eye”.

Stem diseases

Damping-off

The most common disease affecting seedlings of the tomato plant — usually begins at the base of their stem. Several disease pathogens cause the damping-off disease: The infection thrives in a wet and cool environment. The infected plant stem appears wet and withered.

Alternaria stem canker ( Alternaria alternata f. sp. lycopersici)

Alternaria stem canker could also affect the leaves and fruit. The infection leaves a dark brown canker on the plant stem, causing damage. As the canker progresses, they encircle the stem causing it to die.

TOMATO VIRUSES

Viruses require a host to replicate to complete their life cycle. Many plant viruses require a carrier, either as a vector or by mechanical means, to transmit the disease from plant to plant. As plants are immobile, insects largely transmit plant viruses.

Common Tomato Viruses includes;

Tomato mosaic virus (TMV)

Plants infected with the mosaic virus appear deformed and stunted. Symptoms commonly show a yellow appearance or mosaic pattern between leaf veins. The disease gradually results in brown spots on fruits, often reducing yield and causing death.

Tomato spotted wilt virus (TSWV)

The virus causes dark spots on new leaves, with dark streaks later forming on the stem. It also affects the matured fruits by causing mottling of red, orange or yellow.

Tomatoes apex necrosis virus (ToANV)

The whiteflies majorly transmit this virus. The virus attacks several solanaceous crops, including tomatoes. Symptoms include necrosis(death of plant tissue) of leaves, fruits and stem, frequently beginning from the apex(top — growing point of the plant). This later results in stunted plant growth and reduced yield.

PESTS

Whitefly

These white tiny winged insects feed on plant juices, leaving behind a sticky residue or honeydew, which becomes a host for sooty mould. They feed on the fruit and leaves of tomatoes; Transmitting diseases such as tomato yellow leaf curl virus (TYLCV).

Aphids

There are 2(two) species of aphids that infest the tomato plant — green peach aphids and potato aphids (Macrosiphum euphorbiae).

The activities of the slender and striped dark green aphids can lead to wilting and delay in maturity. They are well known viral vectors.

The potato aphids cause severe damages when they are present in great numbers. Plant damage includes; malformed leaves, stunted plants, necrosis, or dead plant tissue. Their excreta (honeydew) also creates an environment favourable to the development of mould. Ultimately, infestations lead to tomato yield reductions.

Flea Beetles

The potentially devastating pest attacks tomato plants on the top and bottom sides. Adults eat foliage, leaving numerous small holes, while larvae feed on roots. Unless they are present in huge numbers, damages can be controlled using preventive methods.

Disease Prevention and pest control

Prevention plays a vital part in curtailing disease infections on your farm. Here are tips to get you on a good track to a disease-free farm.

Crop Rotation.
Choose disease-resistant seed varieties.
Practice proper hygiene and proper drainage to avoid the development of fungal spores.
Remove all disease infected plants debris by burning at the end of the growing season.
Weed frequently.
Mulch your tomatoes.
Keep your foliage dry.
Practice proper spacing.

Pest control

There are also pest resistant/tolerant varieties therefore, understand which insect pest is causing damages, and select a good seed variety.

Other control measures include;

Use of natural enemies.
Crop rotation with non-host species.
Use insecticides such as horticultural oils and insecticidal soaps.
Using silver or aluminium coloured mulch can repel whiteflies and aphids.
Practice proper sanitation.

In conclusion: Tomato plant problems are caused by several factors, including abiotic factors such as environmental conditions, temperature, climatic conditions, and soil ph. Therefore, understand what works for your plant. Make it a priority to obtain seed varieties that are either resistant or tolerant — this will go a long way in saving you from future problems.