Conclusions and Summary
The preliminary results of the experiment described show that there is a great difference in vigor, growth, flowering habit, susceptibility to leaf scorch, winter injury, and infection with a fungus disease tentatively believed to be caused by L. coryli between trees of the Reed and Potomac filbert varieties. In all cases the Potomac variety has been the superior.
It would appear that much of the leaf scorch on filberts experienced in the past has been due to a magnesium deficiency or to an unbalanced condition 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).