ition between magnesium and calcium plus potassium in their
nutrition. The symptoms of magnesium deficiency (scorch), which in
general are similar to those on apple and tung, are described. The data
presented show that liberal applications of potassium alone, or in
combination with nitrogen, resulted in a highly significant increase in
the incidence of leaf scorch due to magnesium deficiency. This in turn
resulted in susceptibility to winter injury, the coefficient of
correlation being 0.97, which means that the severity of the leaf scorch
in August, 1950, would account for 94 percent of the winter injury
sustained.

Applications of 1500 pounds per acre of high-magnesium dolomite,
together with five pounds of Epsom salt per tree in early spring of
1951, did not produce consistent improvement in leaf scorch. It seems
that recovery from magnesium deficiency in filberts is slow after
treatment, just as has been found to be the case in fruit trees (2, 4).

Literature Cited

1. Boynton, Damon, Cain, Carlton J., and Van Geluwe, John
Incipient Magnesium Deficiency in Some New York Apple Orchards.
Proc. Amer. Soc. Hort. Sci. 42:95-100. 1943.
2.----
Magnesium Nutrition of Apple Trees. Soil Sci. 63:53-58. 1947.
3. Drosdoff, Matthew, and Kenworthy, Alvin L.
Magnesium Deficiency of Tung Trees. Proc. Amer. Soc. Hort.
Sci. 44:1-7 1944.
4.----, and Lagasse, Felix S.
The Effect of Some Magnesium and Calcium Fertilizers in a
Magnesium Deficiency Bearing Tung Orchard. Proc. Amer. Soc.
Hort. Sci. 56:5-11. 1950.
5. Southwick, Lawrence
Magnesium Deficiency in Massachusetts Apple Orchards. Proc.
Amer. Soc. Hort. Sci. 42:85-94. 1943.
6. Wallace, T.
Magnesium Deficiency of Fruit Trees. Jour. Pom. and Hort. Sci.
17:150-166. 1939.

FOOTNOTES:

[Footnote 10: Principal Horticulturist and Horticulturist, respectively,
U. S. Department of Agriculture, Bureau Plant Industry, Soils, and
Agricultural Engineering, Beltsville, Md.]

[Footnote 11: Numbers in parenthesis refer to Literature cited, p. 55.]

[Footnote 12: The authors take this opportunity to thank Dr. Harald E.
Hammar for making the chemical analyses of the leaf samples.]

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 Admi