Crown Rot

Strawberry infection by Phytophthora cactorum occurs on poorly drained, over irrigated soils, or during long periods of rain in warm climates. Symptoms of disease are enhanced during periods of high water need, such as after transplants are set, during hot dry weather, or as the fruit load increases. The pathogen has become very important in the last 10-15 years (1999-2014).

Symptoms and signs
he most diagnostic feature of plants with advanced symptoms is a collapse of plants and a deep dark red discoloration of the crown. Stunting of plants or wilting of young leaves are the first symptoms and may appear at any time during the season. Infected plants may remain stunted, or foliage may turn bluish and the entire plant may wilt rapidly until total collapse. Wilting is often accompanied by “draught” symptoms on the leaves such as browning of leaf margins often progressing between the veins and a sharp line between damaged and healthy tissue. Plants may break freely at the upper part of the crown when pulled for sampling. Plants may occur in low lying areas and then are often clustered, or they may appear more in a scattered pattern, especially if the disease came on infected plants. When the crown is first infected, a longitudinal section reveals watersoaked and light brown tissue, but, as disease progresses, extensive necrosis appears that is uniformly brown and not restricted to the vascular tissue. The dark brown discoloration may appear at the base, middle or top of the crown. Roots attached to the affected crown area are frequently black at the point of attachment and commonly have diagnostic oospores in the root tissue. Root systems are also frequently discolored and have a low level of fibrous (secondary and tertiary) roots. In contrast, tissue infected by the anthracose pathogen (anthracnose crown rot) takes on a darker cinnamon color, is more firm, often has a “marbled” appearance and roots tend to remain white to brown at the point of attachment. Also, the root system tends to remain fibrous with a healthy white appearance.

The disease can appear in plug production facilities introduced on infected tips or through contaminated water sources. Tips fail to root, the roots turn black, and the lower petioles of the leaves turn dark brown to black. Plug plants will die or remain stunted especially once frequent watering stops.

Phytophthora crown rot may be confused with anthracnose crown rot. A series of different symptoms and diagnostic steps can be taken to discern between the two crown rot problems.