The weather changes of late summer and early fall are often favourable for leaf diseases on strawberries. Rainy weather extended wetting periods and heavy dews, all contribute to the buildup of spots, blotches and purplish lesions.

A couple of well-timed fungicides in late summer will help to control this problem. Depending on the disease complex present, different fungicides have their strengths and weaknesses . Identifying which leaf diseases are present is the first step in choosing the best fungicide. See table 4-21, of OMAFRA Publication 360, Guide to Fruit Production, to learn which fungicides provide the best control of leaf diseases. For details on biology and life cycle of these diseases, see Ontario.ca/cropipm.

Common leaf spot

This fungal disease can be especially severe on Mira and Kent. Spots are purple with light centers. Infection occurs through the underside of new leaves, before they are fully expanded.

Figure 1. Common leaf spot

Angular leaf spot

This is a bacterial disease, and is not controlled with most fungicides. Lesions are translucent and look wet. Look for milky ooze in humid conditions. The bacteria in this ooze are easily spread throughout the field by workers , splashing rain or irrigation, and equipment. Use Copper 53W or Tivano to suppress angular leaf spot. If symptoms are showing up now, fall sprays might help to reduce inoculum. All cultivars are susceptible especially Wendy, Annapolis, and Jewel.

Figure 2. Angular leaf spot

Leaf scorch

Research has shown that winter injury is more severe where this fungal disease is abundant. Look for solid purple blotches , without a white center or border. Kent and Clancy are good indicator varieties for leaf scorch.

Figure 3. Leaf scorch

Leaf blight

Caused by the fungus phomopsis, leaf blight is common on Governor Simcoe. We saw it on Malwina this year as well. Lesions are multi-coloured and often v-shaped, progressing inward from a leaf edge.

Figure 4. Leaf blight

Powdery mildew

This fungal disease causes a range of confusing symptoms, from diffuse reddish specking, to a reddish-brown scorch. Often, affected leaves are curled upwards, causing a pinkish burn on the underside of the leaf. Very faint white powdery patches can sometimes be seen on the lower leaf surface when infections are new.

Figure 5. Powdery mildew