Leaf spot is the most common foliar disease affecting strawberry on Long Island. It is typically first seen in early May. Cool, rainy weather provides conditions favorable for disease development. Symptoms are small, round, white to tan leaf spots that typically are surrounded by dark purple to reddish tissue that varies in shape from a halo to a large sometimes v-shaped area encompassing several of the leaf spots. The spots typically remain discrete in contrast with leaf scorch, another disease occurring on Long Island.
Leaf spot is more likely to occur in older plantings where it occurred previously because the pathogen survives in overwintering leaf tissue as well as it produces a survival structure that functions like a seed to enable the pathogen to survive.
Leaf spot can affect yield directly because it causes small black spots on fruit (see black seed disease), and indirectly because leaf death increases likelihood of sunscald. Additionally, where leaf spot becomes severe, plants can be predisposed to winter injury and flower bud production can be inhibited the following year.
The varieties ‘Jewel’, ‘Canoga’, ‘Cardinal’, and ‘Lester’ are considered to have some resistance to leaf spot and also leaf scorch. Cultural management practices include mowing and burying infected leaves at renovation to destroy this carry-over inoculum. Also implement practices that facilitate air moving through the canopy to minimize length of time that leaves are wet, which are needed for infection, including wide plant spacing and good weed management.
Fungicides with mobility in plants and targeted activity that are labeled for leaf spot include Captan, Cabrio. Mettle, Pristine and Rally. These fungicides are also labeled for other diseases of strawberry that occur on Long Island. Captan is labeled for gray mold. Cabrio and Pristine are labeled for anthracnose, gray mold, and powdery mildew. Rally is labeled for powdery mildew and Phomopsis leaf blight. Copper is a good contact fungicide to use with these targeted fungicides; chlorothalonil and mancozeb fungicides are not labeled for this use.
There are copper fungicides approved for organic production.
Please Note: The specific directions on pesticide labels must be adhered to — they supersede these recommendations, if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.
Below: Suspect initial symptoms.