Mulberry Leaf Spot is a common fungal disease that affects trees within the Morus genus, including both ornamental and fruit-bearing varieties. This condition specifically targets the foliage, leading to premature leaf drop and a reduction in the tree’s ability to photosynthesize effectively. This guide provides clear steps for identifying the symptoms and implementing immediate and long-term strategies to protect your mulberry tree.
Identifying the Visible Symptoms
The first signs of infection typically appear in the spring as small, irregular spots on the leaves. Initially, these lesions may present as dark brown, reddish, or purplish specks, often surrounded by a pale-green or yellow halo. As the disease progresses, these spots expand in size and change their appearance.
The center of the lesion often dries out, turning pale gray, tan, or whitish, while the outer margin remains dark. Multiple spots may merge, forming larger necrotic areas on the leaf surface. Severe infection reduces the functional leaf area, leading to widespread yellowing before the leaves prematurely drop. This early defoliation is the most noticeable effect and can significantly stress a young or weakened tree.
The Fungal Cause and Disease Spread
Mulberry Leaf Spot is caused by several related fungal pathogens, most commonly Cercospora moricola. These fungi survive the winter primarily within fallen, infected leaves and other plant debris beneath the tree, producing spores when favorable environmental conditions return.
The disease cycle is triggered by warm temperatures (typically 24 to 26 degrees Celsius) combined with high relative humidity (often above 70 percent). Spores are primarily dispersed by rain splash and wind, landing on wet leaf surfaces where they germinate and penetrate the tissue. Prolonged leaf wetness is a significant factor in facilitating infection and spread throughout the tree canopy.
Immediate Treatment Options
Active intervention begins with the immediate physical removal of infected material to reduce fungal inoculum. Carefully prune and destroy any branches or leaves showing significant spotting, sanitizing pruning tools afterward with a household disinfectant solution.
For chemical intervention, protective fungicides are the standard approach and must be applied early in the season upon the first sighting of symptoms. Effective options include broad-spectrum protectants like chlorothalonil or copper-based fungicides. These chemicals create a barrier on the leaf surface that prevents fungal spores from germinating. Application typically needs to be repeated every seven to ten days, especially following heavy rainfall, as the protective layer can be washed away. If the mulberry fruit is intended for consumption, confirm the chosen fungicide is approved for use on edible crops.
Cultural Practices for Prevention
Long-term management relies heavily on breaking the disease cycle through rigorous cultural practices. The most effective step is thorough sanitation beneath the tree, involving the raking and removal of all fallen leaves and debris in the autumn and winter. Disposing of this material, rather than composting it, eliminates the primary location where the fungus overwinters.
Improving air circulation minimizes the duration of leaf wetness. This is achieved by selectively thinning dense inner branches, allowing better airflow and sunlight penetration to dry the leaves quickly. Adjust watering techniques to avoid overhead sprinkling; instead, apply water directly to the root zone, preferably in the morning, ensuring the leaves dry completely before evening.