Strawberry Leaf Spot Control

Causal Agent

• Strawberry leaf spot is caused by an infection from the Mycosphaerella fragariae fungus. The imperfect stage of the fungus is referred to as Ramularia tulasnei. The fungus has no other host plants besides strawberry. Leaf spot disease is most commonly seen on plants between early and midspring.

Symptoms

• The disease is characterized by the appearance of 1/8- to 1/4-inch, reddish purple to dark purple spots on upper foliage surfaces of infected plants. With disease progression, the spots spread to the petioles, runners, fruit stalks and calyxes or caps of fruit. The spots gradually develop tan, gray or white centers. Fungal fruiting bodies in the form of dark specks are visible on older lesions. Tan or bluish areas form on foliage undersides.

Favorable Conditions

• The fungus only infects the young and succulent plant areas. The fungus overwinters on infected older foliage in the planting areas. The spores are then splashed onto new plants with spring rains and water, giving rise to the infection. It takes 10 to 14 days from infection time to appearance of symptoms. Fungal growth is most rapid in 65 to 75 degree Fahrenheit weather. Hot and dry weather reduces the spread of infection. The young and expanding foliage is most prone to the disease. Frequent rains during early and midspring often a cause for leaf spot epidemics in strawberry plantings.

Control

• Start control of leaf spot by choosing disease resistant strawberry varieties that are best suited for the growing region. Purchase disease free plants from reliable sources. Plant strawberries in a well ventilated and sunny site and pay attention to weed control. Avoid fertilizing with nitrogen during spring to reduce production of young foliage susceptible to fungus. Chemical control options include the use of products containing triflumizole, chlorothalonil or myclobutanil.