Strawberry Leaf Spot

Strawberry leaf spot, caused by the fungus Mycosphaerella fragariae, is one of the most common foliar diseases in commercial and home strawberry plantings across North America. The pathogen overwinters in infected leaf tissue and disperses primarily by water splash during rain or overhead irrigation. Spore germination is favored by temperatures between 65°F and 75°F combined with prolonged leaf wetness, conditions that occur regularly during spring growth and again in fall for everbearing types.

Symptoms begin as small, circular purple spots on the upper leaf surface. As lesions mature, the centers fade to white or gray while the purple border persists, giving the spots their characteristic bull's-eye appearance. In heavy infections, spots coalesce, leaves yellow and weaken, and premature defoliation follows. Plant vigor and berry size both suffer when a significant portion of the canopy is lost mid-season.

For June-bearing beds, annual renovation after harvest is the single most cost-effective practice. Mowing off old foliage and removing debris breaks the disease cycle before fall growth resumes. Wide in-row spacing and avoiding overhead irrigation reduce the leaf wetness periods that favor spore germination. In regions with historically high disease pressure, a targeted fungicide program applied at early leaf emergence can suppress early-season inoculum. Resistant varieties are available and represent the lowest-input long-term solution; consult regional extension trial data to identify varieties with documented resistance that also perform well in your zone. Sanitation throughout the season, clearing dead and infected leaves rather than leaving them to decompose in the bed, provides incremental but meaningful suppression.