This Live oak was diagnosed with Phytophthora and confirmed through DNA lab tests. The disease has progressed to the crown causing thinning of the canopy and dieback on some limbs.
All of these Live oaks tested positive for Phytophthora. Only a few showed symptoms but it had spread through the soil.
Phytophthora spp. (also known as root rot or crown rot) is a destructive pathogen in the genus of oomycetes or water molds responsible for damage to crops, plants, shrubs, and trees. (The Great Potato Famine in Ireland was caused by Phytophthora infestans. Phytophthora ramorum is a species best known for sudden oak death (SOD) in Texas.) It was previously believed to be a fungus but unlike the cell walls of fungi, which are primarily made of glucans, chitin, and glycoproteins, Phytophthora cell walls are made of cellulose. There are approximately 200 species of Phytophthora known and up to 500 species are estimated yet to be discovered. Phytophthora is a soil-borne pathogen that can survive in slightly moist soil for long periods. It is easily spread in several different ways. Rain and wind, water run-off, tree-dwelling animals carrying it from one tree to another, and of course man. Walking across infected soil, transplanting infected plants, and equipment that hasn’t been cleaned properly, and cutting infected trees allowing air-borne spread. Yes, Phytophthora can enter a tree through contact with either roots or leaves. Phytophthora is especially damaging when the soil around the base of trees remains wet. Good drainage is key to reducing the spread. Trees with weed fabric or plastic around the base are prime for infection since the moisture in the soil can not evaporate and the soil can become sterilized of nutrients.
Phytophthora causes decay in roots and dries out the leaves of trees, which can take months to years before symptoms appear, almost mimicking Oak wilt. A few visual observations can help differentiate between the two. This is important when treating sick trees so that the proper chemical is used. The leaves affected by both pathogens are very similar with just a few differences. Oak wilt leaves can have veinal necrosis which will show through on both sides of a leaf. Phytophthora leaves can have veinal necrosis but it will not show through on the back of the leaf. Leaves can show margin burn or tip burn from both pathogens but the Phytophthora leaf will look “damp” and not “crispy” like an Oak wilt leaf. Yellowing or browning and curling of leaves is also an indicator. Phytophthora is not host-specific like Oak wilt and can be treated with the proper fungicide. Don’t let someone look at your trees and diagnose them with Oak wilt and treat them if they haven’t done a thorough investigation or offered to take a lab sample. A simple test can make all the difference. If you have a tree that shows symptoms like this give Rockoff Tree Solutions a call.
Example of Phytophthora leaves. 
Example of Oak wilt leaves.