Berry Disease of the Month
Inspired by Tom Volk's "Fungus of the Month", Cornell's Tree Fruit and Berry Pathology program will feature a berry crop disease each month starting January 2009. Symptom pictures and key disease information will be presented through a series of simplified questions. Please understand, I will not reccomend specific chemical management products. Past Diseases of the Month, will remain on the site to be used as a reference.
Click here for Past Diseases of the Month
Berry Disease of January 2009 is:
Common Leaf Spot of Strawberry!
What is it? Common leaf spot is a ubiquitous foliar disease of strawberries. The disease is found in almost every New York strawberry planting.
What causes it? The disease is caused by a fungus called Mycosphaerella fragariae. This fungus survives in dead infected plant litter as hard black structures called sclerotia or as microscopic spores called conidia.
How do you get it? In the spring, the fungus breaks dormancy just like the strawberry plant, and releases its spores into the environment. The spores spread about the planting during warm rains. Young tender leaves of strawberries become infected by the fungal spores and eventually produce more of the fungus’ spores.
What does it look like? The disease looks like numerous tiny purple spots (1-2/8s) of an inch in diameter) with grayish white centers covering the surface of strawberry leaves. The number of spots per leaf and the severity of the disease throughout the planting depend on the amount of the fungus (inoculum) in dead planting material at the site. If the infection is too severe, the plants can defoliate.
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Common leaf spot symptoms developing on strawberry foliage |
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Mature common leaf spot symptoms on the surface of strawberry foliage. This level of spotting throughout a planting would represent a “severe” level of infection. |
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| Common leaf spot fungus surving on dead plant material. This is a major source of spring infection (inoculum). | ||
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| Young strawberry plant compromised by common leaf spot infection | ||
| Pictures provide by C. Heidenreich | ||
What will it do to my planting? This disease is fairly harmless and won’t impact production unless the spotting is severe. Indeed, the disease reduces photosynthesis, but unless your planting begins to defoliate from the disease, the impact on yield is likely to be negligible.
What do I do about it? Fungi like warm, wet, dark conditions and thrive on dead plant material. Therefore, it’s really important keep weeds out of the planting and not to crowd strawberry plants by employing tight within-row spacing. Since the fungus survives the winter on dead plant material, it’s vital to remove and destroy plant material during renovation.
What do I SPRAY? You really only need to make a fungicide application if you had a high level of leaf spot the previous year. If you decide to apply a fungicide, make the application dormant or delayed dormant to reduce the “inoculum” before the emergence of young tissue.
Past Berry Diseases of the Month