White Mold

What is White Mold?

White Mold is a common fungal disease that affects a wide range of plants, including vegetables, flowers, and trees. It is caused by the fungus Sclerotinia sclerotiorum and can cause significant damage to crops, especially in cool and moist growing conditions. The disease is characterized by the development of white, cottony fungal growth on infected plant parts, including stems, leaves, and flowers. Over time, the fungal growth can spread and cause the infected plant parts to rot and collapse. This can lead to reduced yields and complete crop loss if left untreated.

White mold can affect a wide range of plants, including:

• Legumes – beans, peas
• Vegetables – cucumbers, cabbage, cauliflower, eggplants, lettuce, peppers, tomatoes
• Ornamentals – petunias, marigolds, zinnias, sunflowers, sage

White Mold is most likely to occur in areas with high humidity, such as in greenhouses, or in regions with cool, wet springs and warm, humid summers. The fungus that causes white mold grows best in temperatures between 60 and 80°F (15-27°C) and requires moisture to thrive, so it is most active when the environment is consistently damp.

How to Identify White Mold?

The symptoms of white mold include:

• Water-soaked, brown to black stems or petioles
• White, fluffy, cottony growth on the leaves, stems, and flowers of the plant.
• Yellowing and wilting of leaves, which can lead to plant death if the infection is severe.
• Dark, sunken spots on fruits and vegetables, which can cause them to rot.
• Stems that become soft and brittle and break easily when touched.
• A characteristic sweet, musty odor, which is a sign that the fungus has started to produce spores of its fruiting body.

This fungal growth produces black, hard, round structures called sclerotia, which can survive in the soil for several years. As the disease progresses, the white mold can spread to the flowers and leaves, causing them to wilt and turn brown.

How Does White Mold Spread?

White Mold spreads through the production of fruiting bodies called apothecia, which release ascospores that can infect new plant tissues. This can happen when spores of infected plant material come into contact with healthy plants or when wind or water carry the spores to new locations.

White mold can also spread via sclerotia, which are hard, dark-colored structures that can survive in the soil for several years and produce new infections when conditions are favorable.

How to Prevent and Control White Mold?

To prevent and control white mold, the following steps can be taken:

• Crop rotation: Avoid planting susceptible crops in the same location year after year. Instead, rotate crops with non-susceptible plants such as cereal grains or corn.
• Proper irrigation: Water the plants only when necessary and avoid overhead irrigation, which can keep the leaves wet for extended periods of time.
• Sanitation: Remove and dispose of infected plant debris and any sclerotia present in the soil.
• Resistant varieties: Plant resistant crop varieties, if available.
• Avoid overcrowding: Overcrowding of plants can contribute to the spread and severity of infections. This is because overcrowded plants can have reduced air circulation, which can create moist and humid conditions that are favorable for the growth and spread of the fungus. Practice proper plant spacing, especially in high-risk crops.
• Minimize plant stress: Provide plants with adequate nutrients and water to minimize stress and improve their overall health and ability to resist infections. High soil fertility, especially using nitrogen-rich manures and fertilizers, favors white mold development by promoting lush plant growth and early canopy closure.
• Weed control: Weeds can serve as alternate hosts for the pathogen, allowing it to persist in the field from one year to the next. To prevent the spread of white mold, it is important to remove any weed species that can serve as hosts.
• Fungicides: Use fungicides specifically labeled for white mold control and follow the recommended application rate and timing.