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Raspberry Root and Crown Rot
This article was published originally on 6/28/1996Phytophthora root rot on raspberries is caused by several species of soil-borne fungi in the genus Phytophthora. Root rot is most common on red raspberries, although purples and blacks may also be affected. Phytophthora has been identified as the cause of the decline of stands of red and purple raspberries previously thought to be suffering from winter injury or "wet feet."
Root rot is most commonly associated with heavy soils or portions of a planting where water accumulates, such as lower ends of rows, dips in the field, etc. Infected canes are often stunted with weak lateral shoots and leaves that yellow prematurely or scorch along the margins and between the veins. Severely infected canes wilt and die as the weather turns warmer before harvest. Over time, fewer new canes emerge from within the diseased patches. New canes may become infected, wilt and die within the first year.
It is important to identify the cause of the wilting symptoms since other entities may cause similar symptoms. Winter injury, cane borers, anthracnose and cane blights can also cause cane dieback. To diagnose Phytophthora root rot, dig up canes which are wilting but not dead, and scrape off the outer layer of tissue (epidermis) from the main roots and crown. On healthy plants this tissue will be white, but on diseased plants, this tissue will be red-brown. Often a distinct line can be seen between the diseased and healthy tissue, especially on the crown.
Since this fungus requires free water to spread, the disease is more severe during periods of excess moisture. If water remains standing and oxygen is depleted from the root zone, the plant becomes less capable of resisting invasion by the fungus.
Year of Publication:
IC-475(17) -- June 28, 1996