Phytophthora trunk rot (collar rot, stem canker)
P. cactorum attacks the roots and trunk of apple and pear trees. Although it is rarely a problem in pear, Phytophthora crown, collar, and root rot is a major problem in apple orchards. Crown rot occurs when the infection is below the soil line, and typically affects the rootstock. Collar rot occurs above the soil line on the lower trunk of the scion. In both cases foliar symptoms are indicative of root or vascular dysfunction. Affected trees exhibit poor terminal growth and become stunted. Upon removal of the periderm, the inner phloem tissue is typically necrotic and orange- to red-brown, and may be dark brown during latter stages of infection. Trees infected with either of these diseases usually decline over several seasons and eventually die.