Determining the most popular tomato diseases

Growing tomatoes is a very popular activity among growers from all over the world. They are a staple ingredient in many dishes all around the world, and it would be disappointing to lose an entire crop to diseases, wouldn't it? 
Tomatoes are susceptible to various pathogens, and the quality and quantity of the harvest depend on how well we prepare for the battle. Taking appropriate measures is crucial for ensuring a bountiful and readily available tomato yield.

What are the dangers of disease to plants

Diseases pose a greater threat to tomatoes (as well as other plants) compared to pests. Parasitic insects primarily target the external parts of plants, making them more visible and susceptible to mechanical removal by picking or shaking them off. Alternatively, the application of an effective insecticide can eliminate them entirely, leaving no chance for survival. However, diseases require a different approach, as they can be more detrimental and challenging to control.

Pathogens have the ability to infiltrate deep into the tissues of plants, making it difficult to detect their presence until visible signs appear. By the time we notice these signs in tomatoes, the infection has often already spread extensively, and our focus shifts from saving the crop to preserving the plants themselves. That's why timely preventive measures are crucial, although some diseases can still be managed even after infection has occurred. 

Let's take a look at the most common tomato diseases:

#1 Phytophthora

The causative agent of the diseases is the fungus Phytophthora infestans. It is the primary cause of concern for tomato growers. This pathogen thrives in environments with low temperatures and high humidity, often occurring during prolonged summer rains or in the latter half of summer and early fall in many regions.

Identifying phytophthora is crucial, as it manifests as numerous brown spots with light-colored borders on the leaves. The undersides of the leaves may exhibit a powdery whitish blotch. If left unchecked, the disease can spread to stems and fruits, causing necrotic spots. Given the rapid spread under favorable conditions, preventing the proliferation of phytophthora becomes paramount but challenging.


For heavily infested plants, fungicides become necessary. However, if you prefer organic farming methods, unfortunately, salvaging infected plants may not be feasible. It's important to note that tomatoes should not be consumed for several weeks after fungicide application. Alternatively, if the disease is in its early stages, biopreparations can be employed, with spraying recommended every 10 days.

#2 Powdery mildew

Powdery mildew, caused by various fungal species, presents a common challenge for tomato growers. Its characteristic appearance includes a whitish (light gray) powdery or spider-like growth on both sides of the leaves, often found in leaf axils, and occasionally on buds or flowers. This fungal disease thrives under moderate temperatures and high humidity, posing a significant risk due to its rapid spread and contagious nature, rather than its direct damage to plants.


To combat powdery mildew, biopreparations can come to the rescue, offering effective protection for your tomato crop. Additionally, implementing agronomic practices such as removing infected plant residues, adopting proper irrigation techniques, and cultivating tomato varieties with relative disease resistance can greatly contribute to managing this issue. By taking these preventive measures, you can safeguard your tomatoes and maintain a thriving crop.

#3 Septoria leaf spot

Septoria leaf spot, caused by the fungi Septoria tritici, poses a significant threat to tomato plants. This disease thrives in conditions of increased humidity and temperature, contributing to its rapid spread. Recognizing the symptoms is crucial - a telltale sign is the appearance of white spots. Initially, light spots with brown edges manifest on the lower, older leaves, gradually spreading to cover most of the foliage, except for the underdeveloped top leaves. The affected leaf surfaces turn yellow, plants lose their turgor, and fruits become flabby.


To combat septoria leaf spot, employing antifungal agents containing copper and other components is recommended. It is crucial to alternate between different fungicides to prevent pathogens from developing resistance. Regular spraying with fungicides should be carried out 3-5 times during the growing season, and treatment during spring and fall soil preparation is mandatory to effectively manage the disease. By implementing these measures, you can protect your tomato plants and promote a healthy crop.

#4 Alternaria leaf spot

Alternaria leaf spot, caused by the fungi Alternaria solani, poses a significant threat to tomato plants, particularly in dry and hot weather conditions. Once infested, dried dark spots appear on the foliage, gradually merging together. On fruits, these spots become brownish, dry, and prone to cracking. Greenhouse tomatoes are particularly vulnerable to this disease.


To effectively combat Alternaria leaf spot, employing a combination of methods is crucial. Creating unfavorable conditions for the fungus is key to preventing its development. If tomato plants show visible signs of infection, prompt action is necessary to save the bushes. The most effective approach is the use of chemical preparations. However, it's important to note that spraying should be done before flowering and fruiting to avoid making the fruits poisonous and unfit for consumption.

The first treatment should be conducted after planting to protect young plants from potential disease. Contact preparations are recommended for this stage. The second treatment involves using contact-system preparations, which provide external protection to the crop and also penetrate the plant's foliage to combat the development of the fungus. By implementing these measures, you can effectively manage Alternaria leaf spot and safeguard the health of your tomato plants.

#5 Anthracnose

Anthracnose, caused by fungi of the genus Colletotrichum, poses a significant threat to tomato plants, particularly in humid weather conditions with elevated temperatures. The disease primarily affects tomato fruits, initially appearing as slightly depressed and softened areas similar to mechanical damage. Over time, these lesions darken, expand, and eventually mummify the fruit.


To combat Anthracnose, it is crucial to take immediate action. Start by removing the affected parts of the plant. Then, spray the tomato bushes with a solution containing 0.1 lb (40 g) of copper chloroxide mixed with 2.2 gallons (10 liters) of water or a 1% Bordeaux mixture. Alternatively, sulfur-containing preparations can also be effective in treating the disease.

Remember, prevention is key in protecting your tomato plants from these common diseases. Maintaining proper plant hygiene, such as removing infected plant debris, practicing crop rotation, and ensuring adequate air circulation, can significantly reduce the risk of disease occurrence.
If you suspect that your tomato plant is diseased, you simply need to use the Plant Doctor feature right away. This way you will know exactly what disease your plant is infected with and how to deal with it effectively.