Because other organisms and injuries can produce symptoms very similar to P. ramorum and Sudden Oak Death, confirmation of P. ramorum can only be done through laboratory diagnosis. Diagnosis of P. ramorum based on visual symptoms is a judgment rather than positive confirmation. Follow these links for more information on true P. ramorum symptoms, diagnostic questions, and how to sample for laboratory testing. Some more common look-alike diseases are described below:

Wetwood - a bacterial infection that is the result of an injury to the tree; like Sudden Oak Death, wetwood also causes bleeding in the trunks and large branches of oak trees. However, Phytophthora ramorum bleeding is sticky and spotty, whereas wetwood bleeding is watery, foul smelling, and usually very copious. 

Hypoxylon – a fungus that looks like dark brown or black balls and grows on dead wood; Hypoxylon is often associated with the later stages of Sudden Oak Death, but can appear on the trunks of trees or logs that are dead or dying from any number of causes.


 

California oakworm - a caterpillar with green or yellow stripes and a round, tan head; Oakworms can cause heavy to complete defoliation of coast live oaks, making the tree look as though it is dead or dying. Tree twigs and buds are alive though, and caterpillars will likely be visible, as will accumulations of droppings, or frass, beneath the tree. Infested trees usually releaf in the spring; a tree is rarely defoliated two years in a row.

Foliar host look-alike symptoms - Foliar hosts can be damaged by the sun or other fungi, causing symptoms similar to Phytophthora ramorum on leaves. Other hosts lose their leaves in the summer, or display browning foliage during drought conditions. These symptoms can make foliar hosts look as though they have Phytophthora ramorum, but only laboratory testing can ensure an accurate diagnosis.