Strawberry plants are susceptible to several fungal diseases that affect the leaves and green areas of plants. The diseases weaken the plants, resulting in an economic loss for production farmers. The disease will infect single plants and move to others as the infection advances. Following control and preventative measures will decrease crop destruction and increase fruit production.
There are three leaf diseases that affect strawberry plants in North America. Leaf spot is a fungal disease that is also called strawberry rust. This disease infects all green areas of the plant including the leaves, runners, stalks and fruit caps during spring growth. Leaf scorch is a fungal disease that infects the green areas of strawberry plants in the same manner as leaf spot. Leaf blight is a fungal disease that infects the leaves of strawberry plants after harvest.
Leaf spot infects the green areas of strawberry plants, showing purple red colored specks or spots. The spots will change color from tan to white as the disease matures. The fungus affects new, young growth on the plants. In wet conditions, the leaf spot fungus infects the berries and creates spots around groups of seeds. Leaf scorch shows similar symptoms as leaf spot, except as the fungus matures the spots become black in color. As the leaves become infected with leaf scorch, they eventually take on a dried or scorched appearance. The lesions with leaf scorch may spread and cause flowers and young berries to die. Leaf blight forms on the leaves presenting a purple red colored lesion that forms a large V on the leaf. Small black dots form on mature areas of infection. Leaf blight affects older or weak plants more than healthy new growth.
Leaf spot, leaf scorch, and leaf blight are caused by fungus that infects the plant. The fungus produces spores that thrive in wet, warm conditions. The fungus will over winter, which is the primary cause of infection. Since the fungus remains present in the area, it will infect new plants if not properly controlled.
At the first signs of infection, remove and destroy all leaves and runners presenting symptoms. Plant new sets in areas that have good air circulation along with a sunny, well drained soil. Control weeds around the plants as they prevent air circulation and drying of the plants. Weeds stay wet longer, creating an optimal environment for fungus growth. Fungicides will assist in controlling the disease; however it is better to use organic methods of control.
The best prevention of fungal disease in strawberries is planting resistant varieties. The Tribute and Tristar varieties are listed as being resistant to both leaf spot and leaf scorch. There are no varieties that are resistant to leaf blight at this time. Contact your local University Extension Horticulture Agent for information on varieties that work well in your area.