Phytophthora Root Rot

Phytophthora is a very dangerous fungal incurable disease of blackberries

Blackberries that were planted in the wet soil conditions or periods of flooding are often susceptible to Phytophthora root rot.
The disease is caused by Phytophthora fragariae Hickman. These soilborne pathogens are most often associated with heavy soils (with low amount of oxygen) and poorly drained areas. Excess water not only promotes susceptibility of roots to this disease, but also aids the fungus in moving to new infection sites. New infections occur when the pathogen releases motile spores that are carried via water to susceptible hosts. These swimming spores also enable the organism to spread from plant to plant. Spores may also be moved considerable distances in contaminated soil. Low air temperatures enhance the susceptibility to Phytophthora root rot.
Disease symptoms may first become noticeable in the spring, initially occurring in areas of the planting that are low or poorly drained. Foliar symptoms can include marginal browning, red or purple coloration, and (or) chlorosis. Off-color leaves may also be smaller than normal. Infected plants show low vigor, developing fewer canes than usual. The canes may be weak and stunted. Wilt is sometimes associated with this disease. Stressed plants become more susceptible to other diseases, as well as to winter injury. Severely infected plants collapse and die. None of these symptoms alone are definitive for Phytophthora root rot since other factors, such as prolonged flooding or canker diseases, can result in similar symptoms.
Diagnosis requires a careful examination of the main roots and crown of dying (not yet dead) plants. The tissue beneath the root epidermis or bark is white on healthy roots, while a typical reddish-brown discoloration is evident with Phytophthora-infected roots. Often a clear line of demarcation can be observed between diseased and healthy portions of the root.
Disease management includes right site selection, improving soil drainage, healthy bushes planting and fungicide using. Note, that fungicides will not cure infected plants. Infected plants must be removed and destroyed. Good results was received with Ridomil Gold and Aliette fungicides. But these chemical controls are not effective if the cultural controls (as wrote above) are not followed.

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