nistration, Bureau of Plant Industry, Soils, and
Agricultural Engineering, Division of Fruit & Vegetable Crops and
Diseases, Plant Industry Station, Beltsville, Maryland_

Introduction

For the past several years observations have been made on the
development and spread of the bunch (brooming)[13] disease on _Juglans
nigra_ and on other species of walnut growing in the orchards at Plant
Industry Station at Beltsville, Maryland. Because of the widespread
interest in growing walnuts a brief survey of these observations will be
given in this paper together with a summary of the history of the
disease and a discussion of its possible effect on walnut production.

History of the Disease

The bunch disease of walnut has been known for years. Waite[14] in 1932
said, "It turned up in Delaware several years ago, where quite a variety
of walnuts, including the Persian, the Japanese Group, and the American
Black Walnut, were found to be affected. At Arlington Farm, Virginia,
during the past 15 years it has boldly riddled the collection of nut
trees assembled in the grounds for study and ornamental purposes."
Photographs made in 1914 of Japanese walnut trees growing in Georgia and
thought to be affected by rosette (now known to be caused by zinc
deficiency) have been found in the files of the U. S. Department of
Agriculture. Now that the symptoms of the two different disorders are
known, it seems clear that the bunch disease was present in those two
states at that early date.

Becker,[15] of Climax, Michigan in 1940 reported on his observation of
this disease in that area. He reports that he observed several cases of
it on Persian walnut, Japanese walnut, and butternut, in addition to
many diseased eastern black walnuts. He says, "My conclusions are that
in witches'-broom (bunch disease) we have a very bad disease that
threatens the black walnut trees everywhere".

In 1939, the late Howard E. Parsons, pathologist of the U. S. Department
of Agriculture, made an inspection trip to Climax and other areas in
Michigan where he studied and photographed diseased trees. Parsons at
that time was working on a similar disease of pecan and water hickory
and was of the opinion that the disease found on the various species of
walnuts in Michigan was similar to the one he was studying.

For the past 20 years the bunch disease of walnuts has been under
observation by the writers and it seems clear that its incidence has
increased great