Nothing compares to the taste of a freshly picked tomato. And when your plants remain healthy, you can harvest these tasty treats all season long.
But, no matter how often we tend to our plants, sometimes a disease affects our garden and the tomato plants suffer. These diseases can affect everyone from the gardener with just one patio tomato to the farmer with an acre-sized plot.
Read on for a listing of the 10 most common diseases that affect tomato plants plus tips to cure and prevent infection.
Many diseases can be prevented with the right planting methods and good practices:
- Plant tomatoes far enough apart to provide good air circulation and do not water overhead.
- Destroy any infected plants at the end of the growing season.
- Do not compost these plants as they can re-infest your garden next year.
- Sanitize your tools between uses.
Common Tomato Diseases
- Early Blight - Early blight will normally first appear on the lower leaves of the plant in the form of leaf spots that are either brown or black. The lesions will then form concentric rings like a target. The leaf spots will eventually migrate to the stem and even the fruit of the tomato. Early blight normally occurs during hot weather when there has been a significant amount of rain and humidity. A fungicide can help to reduce the damage but it will only lessen, not eliminate the issue. The best treatment is prevention.
- Late Blight - Late blight is very destructive and usually occurs when late-season temperatures are cool and dew is heavy. Small lesions that resemble dark, water-soaked spots will appear on the stems, leaves or fruit. Once late blight has been identified, you will want to remove all debris and fallen fruit from the area to prevent overwintering of the disease. Repeated fungicides throughout the growing season can help protect from late blight.
- Southern Blight - Southern blight most often occurs in the summer months when the soil is warm and moist. Discolored lower leaves, wilted foliage and plant collapse are symptoms of this disease that usually results in the death of the plant. Good sanitation is the best treatment. This includes disinfecting any garden tools used, removing and destroying diseased plants along with any garden debris or mulch that has come in contact with them. The soil itself may need to be sanitized as well.
If a blight occurs in your garden, do not plant any other tomatoes or nightshade family members in that area for at least one year.
- Fusarium Wilt - Wilting is the first sign and as the disease progresses, leaves yellow, fade and new growth becomes stunted. Many times Fusarium wilt will attack just one half of the leaf or one half of the plant before it moves to the other.
- Verticillium Wilt - Verticillium wilt presents the same leaf symptoms as fusarium wilt but it will attack both sides of the plant at once. The leaves will curl, wilt, discolor and then die and drop off the plant. Verticillium wilt cannot be cured. Once it has entered the plant, the plants need to be removed and destroyed. The disease will remain in the soil after you remove the plant so be sure to choose resistant varieties in future plantings.
- Anthracnose - Small circular bruised spots develop on the skin of both green and ripe fruits which invite other fungi to infect the interior of the fruit. As the disease progresses, the lesions get larger, deeper and darker. Usually wet weather, poor drainage or splashing water provides ideal conditions for disease development but the fungus can also survive in old plant debris or contained in seeds. To prevent this fruit rot, water at the base of the plant to prevent splashing and wet leaves, harvest fruits as soon as they are ripe and clean up the previous season’s plant debris. Copper based fungicides can be applied when the plants form their first fruit cluster as another act of anthracnose prevention.
- Molds & Mildews - Molds and mildews usually crop up when plants are spaced too closely, resulting in poor air circulation. They are easy to diagnose as a white or gray powdery substance will appear on the surface of the leaves, almost as if it were dusted with flour. With time, the whitish leaves may turn brown, shrivel up and become dry and brittle. This disease can be controlled if you begin fungicide applications at the first sign of mildew. Neem oil, sulfur sprays and products containing potassium bicarbonate are all helpful.
- Tomato Leaf Curl - Tomato leaf curl appears just as it sounds, the leaves become curled and deformed. Though it can take weeks before any symptoms develop, the most common indicator is the yellowing and upward curling of the leaves. The plant growth may also become stunted, taking on a bush-like growth habit. Flowers will not develop and those that do, simply drop off. If you believe your plant has developed a viral infection, removal of the infected plants is necessary to prevent any further transmission to other plants nearby.
- Septoria Leaf Spot - Septoria leaf spot is a disease first evident on the oldest leaves of the plant. It is easily identified from other leaf disorders with its quarter-inch sunken water spots with brown edges and lighter tan centers. The plant will decline in vigor once it has been infected. It can be spread by wind or rain and flourishes in temperatures of 60-80 degrees F. (15-26 C.) Treatment can be applied on a 7 to 10 day schedule beginning after blossom drop when the first fruits are visible.
- Bacterial Speck - This less common disease is unsightly, but not fatal to the plant. The symptoms show as small brown spots with an outer yellow ring. The spots are small but may often overlap, making them look even larger and irregular. In severe cases, the spots will spread to the fruit. As with most tomato diseases, there is no treatment once bacterial speck sets in. If you can deal with the ugly spots, you can leave the plants in the garden until the end of harvest. At the end of the season, discard and destroy any affected plants and rotate your crop to prevent infection the next year.
If you choose to use a fungicide spray on your ailing plants, there are safe-to-use products on the market for home use, many of which are organic. Common fungicides include mancozeb, chlorothalonil, potassium bicarbonate, neem oil and copper based products. Always consult the label carefully for instructions on rate and method of application.
For an easy, affordable and effective treatment, try a DIY homemade fungicide using ingredients you may already have on hand including baking soda, dishwashing soap and cooking oils.
Disease Resistant Varieties
Another option to control these common diseases is to grow hybrids that are disease resistant.
If you have had disease issues in your garden in the past years, select a variety that is resistant to that particular disease. You can find a listing of codes on the back of the plant label. For example, the letter V represents Verticillium wilt resistance while EB is resistant to early blight.
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Amy Draiss, Digital Community Manager at Gardening Know How since 2021, seamlessly blends her hands-on gardening experience with a digital green thumb. With roots in family landscaping and management at a garden center, Amy has cultivated expertise in plants, supplies, and customer relations. Residing in the Midwest, Amy tends to her two-acre haven, showcasing a diverse range of trees, shrubs, and perennials. As the Hydrangea Queen, she shares her love for these blooms and imparts gardening wisdom through videos and social media. Beyond gardening, Amy enjoys quality time with her family, travel, and theme parks. Amy's mission is to inspire and advise plant enthusiasts, fostering flourishing gardens for both seasoned and budding gardeners alike.
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