Relation of Magnesium Deficiency to Leaf Scorch, Winter Injury, and Fungus Infection
On August 15, 1950, at the time the leaf samples were taken, each tree in the experiment was scored as to the degree of leaf scorch present. In the winter of 1950-51 soil samples were taken from each plot receiving potassium alone and the lime requirement was determined by the Division of Soil and Management and Irrigation, of this Bureau. The lime requirement was found to vary greatly, ranging from 1500 to 6700 pounds per acre. In early spring of 1951, high-magnesium dolomitic lime was applied uniformly at the rate of 1500 pounds per acre and in addition each tree received 5 pounds of Epsom salt.
Each tree in the experiment was scored for degree of winter injury on May 10, 1951. By August 3, leaf scorch was evident on trees in certain treatments and the trees were scored for leaf scorch. At this time it was found in certain treatments that the trees that had not shown any appreciable amount of scorch heretofore had some severely necrotic leaves on them. Careful examination revealed many fruiting bodies of one or more fungi in these necrotic areas. Each tree was, therefore, scored for the presence of this disease, which has been tentatively identified by Paul L. Lentz, of this Bureau, as being caused by Labrella coryli. The data on leaf scorch, winter injury, and the fungus disease are given in table 2.
Table 2. Relation of magnesium deficiency in filbert leaves to leaf scorch, winter injury, and disease caused by Labrella coryli
| Treatment | Ratio Mg (percent) K (percent) | Scorch[1] score (1950) | Winter[2] injury score (spring, 1951) | Scorch[1] score (1951) | Disease[1] score (1951) |
| 1. Nitrogen | .151 | 1 | 4 | 7 | 9 |
| 2. Phosphorus | .210 | 1 | 3 | 1 | 119 |
| 3. Potassium | .094 | 21 | 22 | 24 | 3 |
| 4. Complete | .112 | 2 | 5 | 8 | 11 |
| 5. Nitrogen and potassium | .073 | 13 | 19 | 9 | 5 |
| 6. Check | .167 | 14 | 6 | 6 | 8 |
Note [1] Total plot score for 12 trees; highest possible score 36. The scale for scoring was 0, none; 1, light; 3, severe.
Note [2] Total plot score for 12 trees; highest possible score 48. The scale for scoring winter injury was 0, full leaf, no injury; 1, few dead twigs; 2, half of buds not growing; 3, very large amount of dead twigs; 4, only a few buds growing.
Trees that had received potassium alone had the most severely scorched leaves and more of them on August 15, 1950, followed by those that had received nitrogen plus potassium. The trees that had received nitrogen or phosphorus alone showed practically no scorch, each having a total score of 1; and the complete fertilizer trees a total score of only 2, while those in the check had a total score of 6. These scores indicate that scorch is related to magnesium deficiency or unbalance. There was a close relation between the amount of leaf scorch in August, 1950, and the amount of winter injury, the coefficient of correlation being 0.97, which is very highly significant. This coefficient means that 94 percent of the winter injury sustained could be accounted for by the leaf scorch present the preceding summer and early fall.
The scorch scores of August, 1951, show that there had been no consistent improvement from the magnesium-deficiency condition as a result of the dolomite and Epsom salt applications. The scores for the disease caused by Labrella show that applications of phosphorus alone increased the incidence of the disease and those of potassium alone or potassium plus nitrogen decreased it.
In all cases, the incidence of leaf scorch, winter injury, and disease were strikingly different on the Reed and Potomac varieties. In the summer of 1950, the total scorch score of the Reed variety was 26 and that of the Potomac 18, and in August, 1951, the scores were 36 and 19, respectively. The total winter injury scores were 46 for the Reed variety and 21 for the Potomac. Thus, it is clearly evident that under the conditions of this experiment the Reed variety was much more susceptible to leaf scorch and to the winter injury resulting from magnesium deficiency or unbalance between magnesium and calcium plus potassium than was the variety Potomac. Furthermore, the total score for the incidence of the disease caused by Labrella coryli on the variety Reed was 38 as compared with 9 for the Potomac variety. It would, therefore, seem that the Reed is about four times as susceptible to infection by this fungus as is the Potomac. Its less vigorous tree growth, susceptibility to leaf scorch, winter injury, and infection by L. coryli may be due to the differences between its nutritional requirements and those of the Potomac variety.