Propagators seldom agree in their choice of a wax and wound dressing. In a series of carefully controlled tests, Sitton (23), found that a rosin and beeswax mixture with a filler gave results with pecans superior to the so-called "cold waxes" or asphalt emulsions. Paraffin and polyvinyl resin are often used for scion covering and to protect newly set buds. Shelton (20) has indicated certain qualities of a satisfactory wax.
The Rootstock Problem
In the Pacific Northwest Painter (16) stated that some Persian walnut varieties on Juglans hindsi (the northern California black walnut) develop a fatal graft blight due to delayed incompatibility at about 20 years of age. This is the so-called black-line disease. McKay (12) found great differences in survival of buds of Chinese chestnut placed on five seedling strains and Hardy (8) suggested that more attention should be paid to the parental relationship of stock and scion in the chestnut. Weschcke (28) reported that black walnuts grafted on butternuts yielded poor crops and that bitternut was a satisfactory stock for shagbark varieties and shagbark hybrids. Smith (25) advocated shagbark stocks for shagbark varieties but found bitternut to be practically as good. Stoke (26), and Smith (25) found eastern black walnut to be the best stock for all walnut species, including heartnuts and butternuts.
Nursery Practices
Commercial nurseries have adopted various methods to discourage the normal tap-rooting habit of nut trees and stimulate lateral and fibrous root production. Planting seed over screen wire, undercutting the seedling each year in the nursery row, frequent transplanting, and root pruning are methods commonly used. Attention must be given to the production of an adequate root system to help the grafted tree withstand the shock of transplanting to its permanent location.
Summary
The chief obstacle to the large scale growing of selected nut varieties is the difficulty in propagation. Careful workers with a background of knowledge and experience and skilled in craftmanship are successful in a limited way. Quantity production is apparently dependent upon specialized facilities and efficient labor programs. The need for extensive rootstock research is keenly felt by growers of walnut, hickory and chestnut.
Literature Cited
1. Barton, Lela V.—Seedling Production in Carya ovata, Juglans cinerea, and Juglans nigra. Cont. Boyce Thompson Inst. 8:1-5. 1936
2. Becker, Gilbert—Notes from Southwestern Michigan. Rept. North. Nut Grow. Assoc. 28:135. 1937