Upper left: Eutypella canker of maple, typical of stem infections of forest trees. Upper right: Fruiting bodies of Polyporus sulphureus, one of the wood-decay fungi. Lower left: A fruiting body of Hydnum erinaceous, one cause of decay in hardwoods. Lower right: Exobasidium fungus gall on azalea, prominent but usually unimportant.

We have begun experiments to get more exact information on the danger of leaving oaks that are poisoned and, if they are a danger, on other methods of making certain that they cannot serve as sources of disease. Since wilt symptoms on white and bur oaks may be limited to a few isolated branches, careful and rigorous pruning of all wilting branches has been reported to prolong the life of an occasional tree.

The development of measures (other than the sanitation of known infection centers) for the control of long-distance, above-ground spread of oak wilt will probably await the discovery of the means of such spread. In many regions, however, oak wilt is not yet firmly established and the number of infection centers are few and small. Prompt elimination of those centers might prevent serious spread of the disease.

The fungus will kill small oak trees, but whether the disease may be spread through shipment of nursery-size trees is not known. There is but little evidence with regard to the hazard dimensional lumber may present in the spread of the disease. However, the fungus has not been isolated from heartwood. Kiln drying should kill the fungus if it were present in sapwood. The fungus is reported to have survived for almost a year in logs with bark on them.

Although the disease is widely scattered through much of our commercially important timber in the Ozarks and Appalachians, the percentage of trees infected is low and no significant losses have occurred. But oak wilt is capable of much destruction; should an efficient vector for the fungus appear, it could become a catastrophe. Research on all aspects of the disease has been started and we hope that a Control of this menace can be found.

THEODORE W. BRETZ, a pathologist in the division of forest pathology, Bureau of Plant Industry, Soils, and Agricultural Engineering, is in charge of the division's investigations of oak wilt, conducted in cooperation with the Missouri Agricultural Experiment Station, at Columbia.