Walnut Crown and Root Rots

Walnut crown and root rots Common name Walnut crown and root rot Phytophthora crown and root rot Causal agent Walnut crown and root rot are caused by soil-borne Phytophthora species, especially in waterlogged areas. Scientific name Phytophthora spp. Symptoms & Signs Walnut crown and root rot can only be identified during the late stages of the disease when the symptoms start appearing overground. Depending on the phytophthora species, the damage may be limited to the root, crown, or trunk base. When the roots are damaged, the plant displays stunted growth, with reduced foliage and chlorotic leaves. The leaves also fall prematurely. In addition, the tissues under the bark also show dark brown cankers with a banded appearance near the margins. Transmission The Phytophthora species produce chlamydospores that germinate to produce zoospores. The zoospores travel through wind and water, enter new plants, and restart their life cycle. It is commonly seen in loamy soil with high water retention capacity. Time of concern Early spring to late summer Common hosts Walnut Almond