We are back this week with our series on the common tree diseases and insect pests in Illinois with a close look at a serious disease that threatens all types of oak trees; oak wilt.  Oak wilt is a dangerous vascular wilt disease caused by the fungus Bretziella fagacearum that oak trees can contract over land or through their roots.  The main symptoms of oak wilt include discoloration and wilting of the leaves and defoliation, and it can kill...