Tomatoes are one of the most easily and commonly cultivated food crops. However, tomato plants are frequently affected by various diseases that can reduce yields. In this article, we’ll explore one of the most frequent and important tomato diseases, the Early Blight of Tomatoes. We will highlight the signs and 5 steps to easily control the disease and protect your tomato yields.
Early Blight of Tomatoes
Early blight is a very common disease that can significantly damage tomato leaves, stems, and fruits causing yield loss. If not managed, the disease can cause up to 80% crop loss. The disease is caused by the fungus Alternaria solani which lives in infected plant debris in the soil. It can also live inside infected tomato seeds. The disease can develop when the fungal materials come in contact with tomato plants by rain splash or irrigation water, especially under warm temperatures (75 F or 24 C) and high humidity. The fungi material will germinate on the tomato leaves and grow inside the plant tissues, causing disease signs and symptoms to develop on the plants.
Signs and Symptoms
Early blight presents as brown, irregularly shaped lesions on tomato leaves, starting from the lower foliage. These lesions may have a target-like appearance with concentric rings, and they can spread up the plant. Infected stems and fruits may show dark and sunken spots.
- Circular, brown spots with dark concentric rings on leaves
- Leaves turning yellow, then drying out and dropping prematurely
- Stem lesions leading to wilting and reduced fruit production
To control tomato early blight begins before planting and continues after planting. You can do the following to manage the disease.
- Choose resistant tomato varieties when possible. Read seed labels or ask seed vendors for a resistant variety for your choice of tomato variety.
- Space plants adequately for good air circulation and sunlight penetration. The optimum spacing for determinate tomato plants is 18 to 24 inches (46 to 60 cm) within rows and 48 to 60 inches (121 to 152 cm) between rows. While that of indeterminate tomatoes is 24 to 36 inches (60 to 90 cm) within rows and 60 to 72 inches (152 to 228 cm) between rows.
- Use mulch to prevent soil splash and stake the plant to keep it upright. Be sure wooden stakes and caging from previous years are not contaminated before being used. Do not use them if previously exposed to early blight unless they are treated with a 10% bleach solution for 30 minutes.
- Remove affected leaves and destroy them; do not compost. Infected plant debris serves as the resting place for the fungal materials. Destroy debris to destroy the source of the disease. Also, pruning lower leaves and stems that are close to the soil surface and can receive soil splash can reduce the disease development.
- Apply fungicides labeled for early blight as a preventive measure in areas previously having early blight. In areas without previous cases, scout for the disease after a period of warm temperature and high humidity and apply fungicides if there are signs that the disease may develop. After at regular intervals afterward as recommended in the fungicide label.
Early blight of tomatoes is a frequent and important disease of tomatoes that can reduce tomato growers’ harvests and return on investment. However, taking proactive measures in engaging the control steps recommended in this article can help to reduce the disease and prevent yield loss. Nevertheless, growers are encouraged to consult their respective local agents before making management decisions. Also, proper caution should be taken when using pesticides on farms to avoid exposure to toxic substances in most pesticides. You can read Steps to Reduce Pesticide Exposure and Residue in Farm Produce: A Vital Guide for New Growers to learn more about how to safely apply pesticides on farms.
* Early blight disease photos from bugwood.org