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Leather rot

Phytophthora cactorum

Leather rot occurs sporadically in Minnesota. The disease infects flowers and fruit at all stages. Infected strawberries have a distinctively unpleasant odor and a strong, bitter taste. Infection of a few ripe berries that are processed into jam can ruin the whole jar with this off-taste.



S. Burkness-Wold, UMN


Infections on green fruit are typically tan to brown areas but occasionally the infected area remains green outlined by a brown margin. As the disease progresses these unripe berries become completely brown and have a rough leathery texture. Infection of ripe fruit may cause little to no color change, or the infected area may become pale, purple or brown. Rot on ripe fruit becomes dry and leathery over time. Both ripe and unripe infected fruit eventually dry down into fruit mummies.

Important biology

The leather rot pathogen is an oomycete; commonly called a water mold. These unique pathogens thrive in wet conditions and produce three types of spores. Oospores are tough resting spores that form in mummified berries and can survive many years in soil. These germinate when soils are saturated to produce sporangia and then zoospores. Zoospores are swimming spores that move through a film of water on the plant or soil to reach susceptible fruit and flowers. Zoospores only need two hours of moisture on the plant surface to start an infection. Once infected, sporangia are produced on fruit and are splashed by rain or irrigation to infect other fruit. The leather rot fungus thrives in areas where water stands for awhile after a rain event.


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