Tomato Powdery Mildew

powdery mildew

Powdery mildew is a common fungal disease affecting many plants, but especially tomato plants.

This type of mildew is caused by many types of fungi that do not require high humidity to get established, and prosper under mild conditions. These qualities make them more prevalent than many other plant diseases. However, this can easily be prevented with an ingredient that has been around for hundreds of years.

Causes and Symptoms

A powdery mildew infection develops when wind borne spores land on plant tissues. A combination of shady conditions and warm weather favor the development and formation of the fungi. The fungi establishes itself through mycelial growth across the surface of the plant. The fungi completes its life cycle by producing more spores; which then perpetuates the cycle throughout the season.

Symptoms of a powdery mildew infection appear as white, chalky spots forming all over the plant, including stems, flowers and fruit. They spread rapidly, affecting large areas of the leaves and stems. The leaves will then turn yellow, die and drop off. Plants will have a lower yield and shortened fruiting season. The fruit flavor will not be as strong as it would have been without the fungal infection.

Treatments and Control

The best treatment for powdery mildews is prevention. Full-sun conditions and high temperatures will hinder its growth and spread. Choosing resistant varieties, providing proper air circulation around the tomato plants, allowing for adequate spacing in the garden, and avoiding overhead sprinkling all work as preventives.

If these measures fail, then fungicides are available for control. Fungicides can be used to protect against and destroy an infection. The least toxic of the fungicides includes neem oil, horticultural oil, sulfur, biological fungicide, and jojoba oil. The oils are better at eradicating infection when symptoms appear, but the sulfur fungicides for tomatoes protect against an infection getting established.

For hundreds of years, applications of sulfur fungicide for tomatoes prevented powdery mildew. They are only useful if applied before symptoms are evident. There are wettable sulfurs and sulfur dusts available for use on tomatoes. Copper can also be used, but it is not as strong as the sulfurs.

Application of treatment, whether sulfer, fungicides, or coppers, only works on contact, and thorough coverage of the plant is critical to stop infection. You should apply fungicides every seven to ten days. If an infection starts to become evident, the oils mentioned above are a reputable alternative to maintain control.

Comments from Other Gardeners
  • Swapnil Tangade says:

    Flusilazole is best for controling powdery mildew

  • Anonymous says:

    Swapnil Tangade–Flusilazol is a toxic substance that should NOT be used in the veggie garden.Try other means, please. It and other products like it are the reason I try to always buy organically raised curcurbits, tomatoes and celery. Dupont can shove products such as these up their collective asses and wait for the tumours to grow.

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