How do you deal with watermelon diseases ? With prevention and learning to recognize them. This fresh summer fruit is in fact subject to rot and fungal diseases , typical of plants that require a lot of water. The fact that the fruits are almost always in direct contact with the ground doesn’t help.

So let’s see what are the most common threats, how to prevent them and how to cure them.

powdery mildew

We have already encountered powdery mildew in the past, talking about sage and fruit plants . However , mildew is a typical disease of cucurbits, which compromises both the development and the taste.

The first symptom, the most evident, are the white spots that spread on the leaves and petioles. If you don’t intervene, the spots get bigger and bigger until the leaves start to turn yellow and fall off. Usually, this last phase occurs in summer, when the weather is hot and muggy due to thunderstorms.

To counteract powdery mildew, Bordeaux mixture or sulfur are used, although it is better not to overdo it. Used in excess, both substances can contaminate the soil and change its pH.

Downy mildew of cucurbits

Downy mildew is another common disease among almost all plants in the garden. We have dedicated an article to onion blight , but there is also a form of the disease that affects cucurbits such as watermelon.

At first, the leaves are covered with small light gray spots , which turn bright yellow over time . As time passes, the spots necrotize and become brownish , the leaves dry out and a grey-purple mold appears on the underside. Above all, the plants stop developing and the fruits do not ripen .

The best way to combat cucurbit blight is to prevent it.

  • Avoid sowing watermelons in fungus-affected spots in your garden unless it’s been a couple of years already.
  • Remove diseased plants .
  • Use drip irrigation , so as to wet the leaves and fruits as little as possible.

Again, use Bordeaux mixture to dab the problem.

Gray rot

Gray rot or botrytis is another disease originating from a fungus: as anticipated in the first lines, watermelon is particularly sensitive to pathologies of this type. The name derives from the ash gray color of the mushroom, which mainly covers the fruits.

The first symptom is a small gray circle on the fruit , which gradually begins to penetrate and spread. Even if the skin remains solid, it turns almost completely gray and the watermelon rots from the inside . The fruits affected by the disease are obviously inedible and impossible to recover. On the other hand, it is possible to prevent the disease.

  • Isolate diseased plants.
  • If you’re using a small cold greenhouse, air it out and make sure the air isn’t too stale.
  • Use sprinkler irrigation and avoid water pooling between flowers and leaves.
  • Space out the plants .

Black rot

Black rot or alternariosis manifests itself with the first heat, when the humidity rate in the air is higher than 65%. Depending on the variety, it can affect both cucurbits and other types of plants, such as cruciferous plants.

The disease manifests itself on leaves and fruits , in the form of large beige spots that become increasingly darker. Left undisturbed, the spots enlarge and form a series of increasingly larger black concentric rings , causing the leaves to progressively desiccate. Above all, the disease also creeps into the fruit , which develops slightly sunken circular lesions covered with mould . The fungus even affects the seeds of the plant, giving rise to an entire generation of already diseased plants.

In watermelons, alternariosis is spread mainly through contact between diseased plants . To minimize the risk, isolate suspect plants and avoid signs of standing water remaining on the leaves.