ey are now
known. Severely affected trees are subject to cold injury, and in
addition the wood becomes very brittle and is easily broken by storms.
Although this disease has been known for several years, it is believed
that its seriousness has not been fully appreciated, as it does not
cause death as soon as symptoms appear. Several years must elapse before
the tree succumbs. In the nut tree plantings made at the Plant Industry
Station at Beltsville, Maryland, large numbers of butternut, Japanese
walnut, and Persian walnut trees were planted. During the following
years, although no records have been kept, several hundred of these
trees have become affected and have been removed. Consequently at the
present time we do not have any butternut or Japanese walnut
trees, and only a few Persian (English) walnut trees left in the
plantings. So far, not a single eastern black walnut tree has been
removed from the orchards because of the bunch disease. Some trees have
shown characteristic symptoms of the disease, but following the removal
of the entire diseased limbs the symptoms have not reappeared.

Possible Effects of Bunch Disease on the Walnut Industry

This disease is known to spread to nearby healthy walnut trees, but the
means by which it is spread or how infection occurs is not known. No
survey has been made to determine whether the disease is present in the
various regions in which walnut trees are grown, and hence it is not
known how widely it is distributed at present. Its spread is probably
associated with an insect vector, and the presence of the vector would
determine whether or not local spread would occur. Much more must be
learned about this disease before its importance and destructive nature
can be fully determined. It seems certain that in localities where the
disease is already present there is little use in planting young trees
of the most susceptible species unless trees in the vicinity that are
already diseased are destroyed. Nurserymen growing trees of the Japanese
walnut, butternut, and Persian walnut should be sure that no diseased
trees which might infect the nursery trees are close to their nurseries.
It is not known how far the inoculum may be carried, but at this time it
would seem that in order to be reasonably safe no diseased tree should
be allowed to grow within a mile radius of a nursery. Infected nursery
trees (or scions) probably constitute the most important means of
long-distance spread