Tomatoes are a classic backyard-garden vegetable that many gardeners grow every year. Harvesting a fresh, plump, bright red tomato right off the plant can be both highly satisfying as well as rewarding. However, if white spots begin to appear on the leaves of your tomato plant, the leaves as well as the tomatoes themselves could be in great jeopardy.
So what are the white spots on tomato leaves? White spots on tomato leaves can be the result of powdery mildew forming on the leaves of tomato plants. When plants receive insufficient sunlight, poor air circulation and high humidity, powdery mildew can begin to form on the leaves of tomato plants causing white spots to appear.
Although powdery mildew doesn’t typically kill tomato plants, it can reduce the yield and even affect the taste of the tomatoes. However, knowing what causes powdery mildew and how to treat it once it starts developing on your tomato plants, you can get rid of it and ensure your tomatoes develop normally.
Causes of Powdery Mildew:
Powdery mildew is a fungal disease caused by several different types of fungi. These fungi thrive in dark, stagnant and moist areas. So when humidity is high, and or your tomato plants aren’t receiving enough sunlight or air circulation, the leaves provide an optimal environment for these fungi to grow and reproduce thus creating the white spots (powdery mildew) to form on the leaves of your tomato plant.
Powdery mildew also tends to target younger, plant leaves rather than older more established ones. Because of this, over fertilization can also contribute to powdery mildew. When tomato plants receive an excess amount of fertilizer and nutrients, growth will accelerate at a much faster rate and the tomato plant will produce lots of fresh, new leaves that are ideal for powdery mildew to thrive on. While fertilizing tomato plants can contribute to a higher tomato yield, over fertilization can be counterintuitive.
How to Treat Powdery Mildew on Tomato Plants:
While powdery mildew can have some adverse effects on your tomato plants there are ways to treat it. Treating powdery mildew is not successful 100% of the time however, the earlier you address it, the higher chance treatment will work.
The first step in treating powdery mildew is to prune the infected leaves. Pruning the leaves will not only help in preventing the spread of powdery mildew to other areas of the plant, it will also improve air circulation which can help prevent powdery mildew in the future.
After you have finished pruning the infected leaves, sanitize your pruning tool. The tool likely has powdery mildew residue on it which can spread to other plants if left unsanitized.
If many or all of your tomato leaves are showing signs of powdery mildew, only prune the most severe leaves. Pruning too many leaves can severely damage or even kill the tomato plant. After pruning is complete, begin treating your tomato leaves with a fungicide.
Neem Oil:
Neem oil is an organic fungicide that works great in treating powdery mildew. In addition to being an organic fungicide, neem oil is also an organic insecticide that repels several different kinds of insects such as aphids, mealybugs and whiteflies, all of which are harmful to tomato plants. Simply spray some neem oil on the infected tomato leaves once a week until symptoms diminish. Click here to check the price of Neem Oil on Amazon.com.
Milk Spray:
If neem oil or other fungicides aren’t available, milk spray is a good alternative for treating powdery mildew on tomato leaves. Combine 2 parts milk with 3 parts water and spray infected tomato leaves with the milk spray. Apply on a weekly basis until symptoms diminish.
Preventing Powdery Mildew:
While treating powdery mildew isn’t always successful, preventing it from occurring in the first place is far more effective. Implementing preventative measures can save you the hassle of treating powdery mildew and ensure your tomato plants develop normally. Follow these steps to minimize the chances of powdery mildew infecting your tomato plants.
Spacing and Pruning:
As mentioned earlier, poor air circulation is a culprit for powdery mildew. This is why adequate spacing is crucial in preventing powdery mildew. Tomato plants should be spaced 18 to 24 inches (46 to 61cm) apart from each other. Overcrowding your garden with plants will prevent air from circulating around them thus making conditions ideal for powdery mildew to form. Give your tomato plants plenty of space to grow and prune the branches and leaves if necessary.
Lighting:
Insufficient lighting is also conducive for powdery mildew. Therefore it’s important to make sure your tomato plants are receiving enough sunlight in order to prevent powdery mildew. 6 to 8 hours of full sunlight is ideal for tomato plants. Tomatoes are sun-loving plants and therefore, should be grown in areas that receive full sun.
Planting Resistant Varieties:
Some varieties of tomatoes are naturally more resistant to powdery mildew. Tomato varieties such as “Granadero” have a higher resistance to powdery mildew compared to most other varieties and should be planted if your garden has a history of powdery mildew contamination.
Other Reasons for White Spots on your Tomatoes:
While powdery mildew is one of the most common reasons for white spots to appear on tomato leaves, it isn’t the only one. If you’ve treated the white spots on your tomato leaves with neem oil and or milk spray and implemented preventative measures but your tomato leaves still have white spots on them, they are likely not the result of powdery mildew but rather something else.
Sun Scalding:
Sometimes tomato leaves will develop white spots on them as a result of sun scalding. When tomato plants are exposed to high amounts of direct sunlight and heat, the leaves may get sun damaged and begin to turn white. This typically occurs when tomatoes are first transplanted outdoors as the plants are used to a shaded indoor environment and are suddenly blasted with an intense brightness and heat when transplanted outside.
Once the tomato leaves begin turning white, they will wither up and fall off the plant. This will inhibit growth of the plant and set back your tomatoes. If tomatoes are already developing on the plant, they may start developing white, blistery areas on them.
The simplest way to protect your tomato plants from excess sunlight is to shade them. When you first transplant your tomatoes from indoors to outdoors, implement a shade cover to give your tomato plant some extra shade and an easier transition to the much brighter environment. After a few days, remove the shade cover and allow the tomato plant to grow in full sun.
Late Blight:
