Bunch Disease of Black Walnut
[Paper expanded from a talk given at the 41st annual meeting of NNGA in 1950.]
John W. McKay, horticulturist, and Harley L. Crane, principal horticulturist, United States Department of Agriculture, Agricultural Research Administration, 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.