Preliminary Report on Growth, Flowering, and Magnesium Deficiency of Reed and Potomac Filbert Varieties

H. L. Crane and J. W. McKay[10]

During the course of filbert breeding investigations at the Plant Industry Station, Beltsville, Md., covering a period of approximately 18 years, the leaves of certain seedlings scorched badly in mid or late summer. Certain other trees showed little or no evidence of this disorder. It was thought that, because filberts thrive best under maritime climatic conditions of cool summers and mild winters, this scorch was probably due to high temperatures accompanied by deficient soil moisture.

This breeding work resulted in the introduction in 1951 of the Reed and Potomac varieties, which were produced as a result of crosses between the American filbert, Corylus americana, and the European filbert, C. avellana. The original trees of these varieties had been under observation for more than 10 years, and their performance had been such as to indicate their suitability for home plantings under eastern conditions. Furthermore, these varieties had shown little or no evidence of scorch and had held their leaves well.

In early spring of 1948, an experimental orchard, consisting of 36 layered trees each of Reed and Potomac, was planted at Beltsville, for the purpose of testing them more fully than had been possible before as to their suitability for eastern conditions. The orchard was designed also for study of their response in tree growth and fruiting to differential fertilizer treatments. Although this experiment has been underway now for only three years, certain of the findings are thought to be of such importance that a preliminary report should be made at this time.

Experimental Plan

The site selected for the orchard is a gentle slope varying from five to 15 percent and providing good air drainage. The soil is a Riverdale (tentative series) sandy loam that had been in orchard grass sod for 10 years before the experiment was begun. Much of the land on the Plant Industry Station farm is now known to be low in available magnesium and potassium. Tree crops, including peaches, pears, and apples, have shown deficiencies of one or both of these elements. The trees were planted 20 feet apart on the contour in pairs, one of each variety in a plot, with six plots in a row. The 36 two-tree plots were in six rows. Thus, the experiment was arranged in a 6 by 6 Latin square and six fertilizer treatments were used. After planting, the trees received frequent cultivation and a uniform application of one pound of 10-6-4 fertilizer. The following spring differential fertilizer treatments were applied: Nitrogen, phosphorus, potassium, complete, nitrogen and potassium, and check. The amounts applied per tree in fractions of a pound were elemental nitrogen 0.2, phosphoric acid, 0.4, and potash 0.2. In the spring of 1950, the amounts applied per tree were doubled; and these same amounts were applied in the spring of 1951. Nitrogen was applied in the form of nitrate of soda, phosphorus as 20 percent superphosphate, and potassium as 50 percent muriate of potash. Strips about six to eight feet wide on each side of the tree rows have been cultivated frequently, but strips of orchard grass sod have been left in the tree row middles to prevent soil erosion. The trees have been sprayed with DDT or parathion or both to control Japanese beetles and mites.

Growth Responses

To determine the growth responses made by the two varieties to the differential fertilizer treatments, diameters of the tree trunks one foot above the soil were measured each spring before growth started. These data are not given here because in 1949 and 1950 there were no significant differences in the growth of the trees as a result of the differential fertilizer treatments. However, trees of the Potomac variety made more growth than those of the Reed variety. At the end of the 1949 and 1950 growing seasons, the average diameters of the tree trunks of the Potomac variety were 16.3 and 25.7 millimeters, respectively; those of the Reed variety were 13.6 and 22.4 millimeters, respectively. The differences 2.7 and 3.3 millimeters, are highly significant. Under the conditions of this experiment, the trees of the Potomac variety are much more vigorous than those of the Reed. The greater vigor of the Potomac trees may account for the fact that they produce suckers much more freely than do trees of the Reed variety. The habit of producing abundant suckers is an advantage in propagating by layering, but it is a disadvantage in orchard trees because the suckers must be removed for optimum nut production. Whether the differences in vigor and suckering habit of the two varieties shown thus far will affect their performance as orchard trees will have to be determined by future observations.

Flowering Response

Each year at the height of the flowering period, each tree in the experiment was rated on the catkins it carried. So far, there has been no effect of the differential fertilizer treatments on the production of catkins. However, there have been very highly significant differences between the Potomac and the Reed. In 1950, only four of the 36 Reed trees produced catkins, whereas 32 of the 36 Potomac trees flowered, and approximately half of them were heavily loaded. In 1951, the number of Reed trees producing catkins was 12 of the 36, whereas 35 Potomac trees flowered. The amount of pistillate flowering during the two years was small on both varieties and not greatly different; this indicates that their nut-bearing potentialities may be about the same. The amount of pollen produced by the Reed variety has always been considered ample for cross-pollinating the Potomac, even though the former has been a light producer of catkins.

Records of dates of flowering of the two original trees over a 10-year period, and of these young orchard trees over a 3-year period, show that there is great variability in time of flowering, depending upon the sequence of weather events each season. Fertilizer treatments have had no measureable effect. The trees have shed pollen as early as January and as late as April, and stigma receptivity sometimes has continued intermittently for two months. The average period of flowering at Beltsville is the last week of February to the first week in March. Both varieties have flowered at the same time under all seasonal conditions observed. This means that additional pollinators will not be necessary when the varieties are planted together in an orchard.

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.

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).

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.

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