Diseases and Insect Pests
In common with most other forms of plant life the trees are susceptible to some insects and diseases.
Reports of injury by the walnut weevil, Conotrachelus juglandis, and also by codling moth larvae have been received. In some cases the foliage is attacked by rust fungi and some injury is also done by leaf spot. Prof. Reed reports witches broom attacking some trees in the South and one case of this disease was observed by the writer in Ontario on a Siebold-butternut hybrid. Notwithstanding these defects it is believed that the Japanese walnut is less attacked by disease and insects than most other species of nut trees.
Opinion of Observers
The opinion of a group of people on the merits or defects of a tree species or project is worthy of consideration. In order to get an expression of opinion as to the merits of the Japanese walnut the following question was asked: Do you consider the better strains of Japanese walnut worthy of more extended planting? The answers to this inquiry were numerous and varied. The great majority were in favor of increased plantings but a few were somewhat dubious. Nearly every one agreed that the species possessed marked beauty and was worthy of more extended planting as an ornamental. Some gave preference to the nuts over the black and English but the majority thought the quality was not quite up to the standard of these two species. Some observers reported favorably on the heartnut for culinary purposes and as an ingredient of ice cream and candy. With these latter comments I have had personal experience and can heartily agree.
Summary
From the evidence furnished by correspondents and from personal observation the good qualities of the Japanese walnut may be summed up as follows:
Rapid growth, marked beauty of form and foliage, early bearing, productiveness, and more than average hardiness to winter cold. The nuts from superior trees are easier to crack than the butternut, hickory and black walnut, but not so easy as the pecan and Persian walnut. These superior varieties yield nuts with a mild flavor which appeals to the taste of many people, but others think the flavor is not quite pronounced enough.
This species crosses readily with the butternut and offers interesting possibilities for the plant breeder.
The trees appear to be somewhat less susceptible to insects and diseases than other walnuts, but this may not always hold good.