Why Are My Watermelons Rotting Before They Are Mature?

Gummy Stem Blight

• While gummy stem blight primarily effects the stems of the watermelon plants, it also can cause the fruit on the stem to begin to rot before it has matured. The disease is caused by a fungus that can spread through the air and water. The fungus is sometimes carried on strong winds and rain. Purchase your seeds or seedling plants from a reputable dealer to reduce the risks of gummy stem blight. If you notice signs of gummy stem blight, which include brown lesions on the leaves and stems as well as oozing lesions on the fruit, you can treat it with a fungicide.

Phytophthora Blight

• If you notice that your watermelons have begun to rot before they have even been ripe enough to pick, they may be suffering from phytophthora blight, another fungus-based disease. This fungus can affect any part of the plant, but it's most often recognized when it affects the watermelons. The main cause of this type of fungus is extremely wet growing conditions. For instance, if there has been a lot of rain that doesn't allow your field to drain properly, those watermelons that are standing in the water may become infected. Therefore, proper drainage is important to prevent infection. If your crop becomes infected, avoid planting any other watermelons in that area for several years because the fungus can live for years in the soil.

Blossom-End Rot

• When your watermelons only rot on the blossom end, or the end that is attached to the vine, you are likely experiencing blossom-end rot. This condition is often caused by the growing conditions in which you grow your crop. Dry winds, wet conditions, lack of calcium in the soil and too much fertilizer can all contribute to this type of rot in your watermelons. This disease spreads from the stem into the fruit, beginning with shriveling of the stem and stretching into fruit rot. If you notice the beginnings of this type of rot, remove the fruit and allow it to ripen off the vine.

Prevention

• While some conditions are beyond your control, you can take steps to help reduce the occurrence of these diseases in your watermelons and maximize your crops. Always plant watermelons in a new location if possible. Plant the watermelons on the top of a mound or hill to provide plenty of drainage to prevent water from sitting in your field and damaging the watermelons while they are young. Use fertilizer that contains calcium sparingly to avoid over-fertilization, while making sure the plants get the calcium they need. Mulching the field with black plastic film also can reduce the occurrence of watermelon rots.