Off-cycle Zythia leaf blotch

We usually see Zythia leaf blotch (caused by Zythia fragariae) during the early spring when plants are small and the weather is cool and wet. With summer planting in Santa Maria occurring in May, especially in fields close to the coastline where fog and heavy dews are common, the same conditions exist (i.e., small plants and cool, wet weather).

In the spring, Zythia is typically short-lived, relegated to the older leaves and does not persist as spring turns to summer. Here’s the catch – in the spring, the days are getting longer and warmer. In September, the days are getting shorter and cooler. So, in September, Zythia leaf blotch has the potential to stay around longer and cause more damage.

Unfortunately, we don’t know how to manage this disease. Conventional wisdom is to leave it alone and it will go away on its own. But in summer plantings, we may need to rethink this laissez-faire strategy. Equally important is to know that this disease is not just a springtime problem but can be a problem whenever cool, wet conditions persist, especially on new plantings.

Refresh your memory of the diagnostic symptoms and signs of this disease (Figs. 1-5).

Figure 1. Classic concentric rings produced by Zythia leaf blotch. This is not a common symptom but very diagnostic when it does occur. (photo by G. Holmes)
Figure 1. Classic concentric rings produced by Zythia leaf blotch. This is not a common symptom but very diagnostic when it does occur. (photo by G. Holmes)
Figure 2. Note the fruiting bodies (tiny dark spots) within the lesion. (photo by G. Holmes)
Figure 2. Note the fruiting bodies (tiny dark spots) within the lesion. (photo by G. Holmes)
Figure 3: After incubation of infected leaves in a moist chamber, 
the oozing of conidia can be observed. (photo by Shashika Hewavitharana)
Figure 3: After incubation of infected leaves in a moist chamber,
the oozing of conidia can be observed. (photo by S. Hewavitharana)
Figure 4: When infected leaf tissue is plated, the same induction of sporulation can be observed. (photo by Shashika Hewavitharana)
Figure 4: When infected leaf tissue is plated, the same induction of sporulation can be observed. (photo by S. Hewavitharana)
Figure 5: The pathogen produces capsule-shaped conidia with two oil bodies visible inside. (photo by Shashika Hewavitharana)
Figure 5: The pathogen produces capsule-shaped conidia with two oil bodies visible inside. (photo by S. Hewavitharana)

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