Symptoms and Diagnosis
Hypoxylon canker is caused by an opportunistic fungi, hypoxylon antropunctatum. Hypoxylon is unable to cause disease in healthy trees but is quick to colonize weakened or dying bark and wood. The Texas Red Oak or Spanish Oak are more susceptible than the Live Oaks or the Post Oaks.

In some areas, red oaks have developed oak wilt symptoms, but also quickly developed additional symptoms of Hypoxylon Canker. Since Hypoxylon Canker infects and kills weakened or stressed trees, it is thought that oak wilt weakens the tree and then Hypoxylon fungus moves in and kills the tree. The oak wilt fungus is not a strong competitor with other fungi, the Hypoxylon fungus is the only one found when laboratory diagnosis is made. The disease is usually associates with stresses caused by drought, heat, wound or chemical injury. Healthy trees are more resistant to the disease.

Symptoms
Leaves of trees infected with Hypoxylon turn yellow and wilt, and the entire branches die, but these symptoms are merely general indicators that the tree is under stress not necessarily caused by the fungi. The bark sloughs off, exposing the stroma, which may appear dusty brown, silver, or white depending on its age as it progresses from it’s asexual to sexual stage. Prior to the bark sloughing, sunken or depressed areas appear in infected areas where the fungus has killed the cambium and sapwood. Fruiting structures eventually cover the cantered area and rupture the bark. Spores produced at a rapid rate and are wind borne to new host.  

Life Cycle
The Fungus is transmitted from one tree to the next by the wind and rain and enters the tree through wounds on the branches and cracks in the bark. As the fungus grows into the cambium and often girdling the tree very quickly killing the cambium and sapwood. Infected branches progressively die back as the fungus moves downward. There is evidence that the fungus may invade young trees but not cause a problem until the tree is under stress.

Control  
No effective means of control are available. Trees infected with Hypoxylon should be removed and properly disposed of, to prevent secondary infections on other susceptible trees. Since the fungus can remain active in dead wood do not chip the wood and use as mulch. Disease prevention can be achieved in high value trees by keeping them healthy and vigorous by fertilization and watering them during drought periods. 

ASIAN AMBROSIA BEETLES