ailed studies are needed,
but at present this Division is not in position to do more than limited,
part-time work on the disease.

The butternut, a widely distributed forest tree of minor importance, is
seriously injured or killed by this disease. The disease severely
damages or kills the Japanese walnut, which has been planted to a
limited extent but is of little importance. According to Dr. Waite's
report, the Persian, or English, walnut is attacked, but very few trees
of this species are planted in the eastern States. Precautions should be
taken to prevent the introduction of this disease into areas where it is
not now present, particularly the western states.

Symptoms expressed by infected trees are viruslike, and Hutchins and
Wester[12] were able to produce the brooming symptoms on a small number
of trees by means of bark patch grafts, indicating that the brooming
disease probably is caused by a virus.

[Illustration: Figure 3.--Brooming disease on black walnut. Ascending
type, upright, sucker growth is typical of this species.]

+Description of Symptoms+

The entire range of symptoms of the brooming disease has not been
determined. Symptoms are recognizable during mid-July but they are most
pronounced during September and October. Curling and cupping of
leaflets, chlorosis, narrowing and basal tapering of leaflets appear to
be associated with early stages of the disease. On severely affected
trees there are distinct broomlike growths at branch terminals, along
primary or secondary branches, or on the main stem to the ground line
(Fig. 2). The broomlike growths are formed by the continuing abnormal
development of normally located buds into short, succulent branches.
Upright, suckerlike branches appear on primary and secondary branches
and on the main stem of the affected tree. (Fig. 3).

The broomed parts usually die back during the dormant period following
their appearance. The dead brooms on trees that appear to be healthy
during the early months of the growing-season indicate that the trees
are infected. Usually the diseased trees, even those severely affected,
exhibit normal growth during the early summer months.

Evidence that walnut trees may be infected for a considerable time prior
to appearance of recognizable symptoms was obtained when 37 per cent of
a total of 300 severely pruned trees exhibited brooming disease
symptoms. These trees had looked healthy until they were pruned.
Unpruned control