for a disease of this type.

Control

The only known method of control of the bunch disease is to prevent
healthy trees from becoming infected. This can be done only by
destroying completely all diseased trees. In the early stage of the
disease, sometimes only one branch on a tree may show symptoms; and
complete removal of this branch may result in the tree's not showing
additional symptoms for a year or more. Except in the case of black
walnut, the disease breaks out again; hence cutting out diseased limbs
cannot be considered a satisfactory control measure, except possibly on
the eastern black walnut.

Case Histories at Beltsville

As a part of walnut breeding work carried on during the past 14 years,
approximately 20 large _nigra_ trees of named horticultural varieties
have been topworked to seedlings of natural first-generation hybrids
between _J. regia_ and _J. nigra_ for the purpose of forcing the
seedling scions into early fruiting. Of these 20 trees, 3 have shown
such unusual behavior as to merit a description of each in the form of a
case history.

_Tree Number 838._ This tree was cut back severely in the spring of
1942, and on August 26, 1943 vigorous new shoots were budded to
47.11-P17, a second-generation seedling of the O'Conner natural
hybrid. The buds grew vigorously in 1944 and early in the season
developed symptoms of the bunch disease. By the end of the growing
season of 1944 the scion limbs were heavy with the typical proliferated
shoots characteristic of the disease. Also, a few vigorous sucker limbs
of the stock tree that grew out from below the point of union of the
scions showed typical symptoms of the disease, although these limbs were
later outgrown by normal shoots and are not now to be seen. In the early
spring of 1945 the diseased limbs were all removed from the tree to
prevent the further spread of the disease in the area.

At the same time that the above seedling was budded in the top of this
tree, a large lateral limb of the stock tree was budded to seedling
number 40.70-P1. This seedling originated from a nut of the Ohio
variety of black walnut that was only about 1/4 the size of nuts typical
of the variety. At the time it was thought that this nut resulted from a
cross of Ohio with pollen of the Persian walnut, as it was produced
under bag and following hand-pollination. Later growth of the seedling
indicated, however, that the pistillate flower was probably pollinated
by _J