Symptoms of Scorch
The visible symptoms of scorch do not begin to appear under conditions at Beltsville until about the middle of July or later. The first symptom is fading of the green color, especially around the margins of the leaf blade. Sometimes this chlorosis results in blotches, which may extend for a considerable distance from the margin towards the mid-rib. This stage is of short duration, as the tissues of marginal chlorotic areas or those of the blotches soon die, roll up, and turn brown. Some leaves show yellow blotchiness over most, if not all, of the surface and this may develop into brown patches of dead tissue or the yellow leaves may fall before the tissues die. The older leaves, those at the base of a shoot, are generally the first to show chlorosis and scorch, and the terminal leaves are the last to show such symptoms. On severely affected trees all the leaves on a shoot may be scorched at the time scorching is observed. Severely affected trees drop part or all of their leaves prematurely. The leaves dropped are those that are scorched or that show yellow blotches. Such trees do not make satisfactory growth, they set few nuts, and the nuts are usually poorly filled at harvest. The symptoms of scorch on filbert leaves are similar in many respects to magnesium-deficiency symptoms on apple (1, 5, 6)[11] and tung leaves (3).
Leaf Analyses[12]
No differences in appearance of the trees as regards leaf scorch were noticed the first year after the differential fertilizer treatments were applied. However, in late July and early August of the second season, severe leaf scorch developed on the trees that had received potassium alone or nitrogen plus potassium, and scorch developed to some extent on the check trees. On August 15, 1950, leaf samples for chemical analyses were taken from each tree in all replications and composited by treatments into six samples. The data on the chemical composition of the leaves as affected by the differential fertilizer treatments are given in table 1.
These data show that the fertilizers applied to the trees were taken up by them and that the composition of the leaves was significantly affected. The trees in treatments 2, 3, and 6, which did not receive nitrogen in the fertilizer, had lower percentages of nitrogen in the leaves than those from the other plots. Their light green color indicated that in the middle of August they were deficient in nitrogen when its concentration was 2.3 percent or less.
Table 1. Chemical composition (oven-dry basis) of filbert leaves collected August 15, 1950, from fertilizer experiment, Beltsville, Md.
| Treatment | Composition of leaves | Ratio | Mg (percent) | |||||
| Ash | N | P | K | Ca | Mg | K (percent) | ||
| % | % | % | % | % | % | |||
| 1. Nitrogen | 6.68 | 2.52 | .129 | .945 | 1.30 | .143 | .151 | |
| 2. Phosphorus | 8.56 | 2.29 | .160 | .885 | 1.60 | .186 | .210 | |
| 3. Potassium | 9.39 | 2.31 | .150 | 1.650 | 1.93 | .155 | .094 | |
| 4. Complete | 7.18 | 2.43 | .133 | 1.175 | 1.63 | .132 | .112 | |
| 5. Nitrogen and potassium | 7.62 | 2.49 | .119 | 1.480 | 1.33 | .110 | .073 | |
| 6. Check | 7.38 | 2.32 | .188 | .890 | 1.70 | .149 | .167 | |
Potassium applications produced the greatest effect on leaf composition, as they increased the concentration of that element in the leaves by 0.285 to 0.760 percentage unit over that in the leaves from the check trees. In addition, it seems likely that this great increase in the potassium content of the leaves was accompanied by a decrease in their magnesium content, since this usually has been found to result. When the ratios of the percentage of magnesium to the percentage of potassium in the leaves were calculated, it was found that they were rather low for the trees that had been fertilized with potassium. The magnesium-potassium ratio was highest in the leaves from the trees fertilized with phosphorus only, followed in order by the check and nitrogen treatments.
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.