Part 19

+Size of crop:+ Nut growers want their trees to bear large annual crops of nuts. It is very seldom that one hears a nut grower express the opinion that a certain tree is carrying too many nuts for the crop to attain proper size and fill well, yet this is very often the case. Furthermore, the production of a large crop of poorly filled nuts one year is almost certain to result in a light crop or none at all the following year. There is a very close inverse relation between the size of the crop produced and the degree to which the nuts are filled at harvest, namely, the larger the crop the less the nuts will be filled. It has been pointed out above that nuts are storage organs, and the food materials required to grow and fill them must be made in the leaves. When too many nuts are set and carried through to the filling period, in proportion to the number of leaves or the leaf area of the tree, it is not possible for the leaves to synthesize the large amount of food materials required to fill the nuts. In pecans, for example, it has been shown that six to eight leaves are required normally to fill a nut properly and 10 or more leaves per nut if the tree is to flower and set a crop the following year. Other ratios for number of leaves or leaf area exist with other kinds of nuts. It is general experience that large crops of nuts remove such large amounts of food materials and minerals from the trees that a light crop or no crop at all is produced the following year. This is especially true if the nuts are not especially well filled in the "on crop year."

+Size of nuts:+ Almost everyone prefers large nuts to small ones, and that is one reason, why the larger sizes command a higher price on the markets. Many remember how popular the McCallister hican was a number of years ago because of its extremely large size. Such varieties of the pecan as Nelson and Mahan were very popular because the nuts produced were generally much larger than those of other varieties. These varieties remained popular until experience in growing them showed that they were very often poorly filled at harvest. As a general rule, large nuts are more difficult to fill properly than small nuts. This is obvious, because much more food material must be made by the leaves and transported to fill the kernels of large nuts than is required to fill an equal number of nuts of smaller size. In seasons with conditions favorable for both tree growth and growth in size of the nuts, it is often the experience that the nuts are poorly filled at harvest. On the other hand, if the weather is dry during the period in which the nuts are growing in size, they are much more likely to be well filled at maturity. In fact, the writer has seen several instances in which, because of severe drought in the spring, pecans were undersized, yet the kernels developed and filled so well that the shells of the nuts cracked at maturity.

+Condition of leaves:+ To produce well filled nuts, nut trees must bear a large leaf area and the leaves must be in good health and vigor. If they are to produce annual crops, the trees must carry their leaves until cold weather in the late fall, undamaged by insects or diseases. The importance of a large leaf area free from injury or abnormal condition is so great that it can hardly be overemphasized in connection with nut production. It can be definitely stated that under normal conditions the size of the crop produced and the degree to which the nuts are filled is directly related to the leaf area and the length of time it is carried by the tree.

If the leaf area is to be large, the trees must make good, strong, vigorous shoot growth, and this means that proper attention must be given to fertilization to insure that the trees have adequate amounts of nitrogen, potassium, magnesium, zinc, and boron, as well as all other essential elements. The elements mentioned have been found most likely to be deficient in the soils of eastern and southern United States. In those regions their lack may be expected most frequently to limit tree growth or the filling of the nuts because of their effects on the leaves and the consequent inability of the leaves to make food materials. Deficiency of one or more of these elements results in leaves that are not able to make food materials in anywhere near such amounts as do normal leaves well supplied with all essential elements. In severe cases, deficiency of one or more of these elements results in chlorosis of the leaves, still later in leaf scorch, and finally in premature leaf fall. Trees having leaves in such condition cannot be expected to fill the nuts borne by them.

Most nut trees grown about home or farmstead are deficient in nitrogen, as the trees must compete with grass, weeds, shrubbery, or other trees. Frequently there is not enough plant food for all. A deficiency of nitrogen limits the growth and the leaf area carried by a tree. A deficiency of potassium or magnesium very greatly limits the amount of food material made by the leaves and hence greatly decreases the filling and the oil content of the kernels. Zinc or boron deficiency has a similar effect.

Hence, to insure the production of well filled nuts, one must be certain that the trees are well fertilized and that the fertilizer elements applied are in proper balance one with the others.

Injury to the leaves resulting from attacks by diseases and insects is one of the most common and important causes of poorly filled nuts. Every species and variety of tree nut suffers from at least one disease or insect pest that damages the leaves and hence limits or curtails the amount of elaborated food materials they can make. In most cases the fungi or bacteria causing foliage diseases infect the leaves in early spring at the time they are unfolding and growing in size, although the infection may not be noticeable until later. These infected areas, even though they are small and not numerous enough to cause the leaf to fall, seriously impair the functioning of the leaf out of all proportion to the area directly affected. Should the infection be so severe as to cause premature defoliation, the damage will be great even though only a small percentage of the leaves falls. The disease of eastern Mack walnut known as leaf spot, or anthracnose, is one of these defoliating diseases that causes untold damage from poorly filled nuts in the current crop year, and results in a small crop or none at all the following year. The development and spread of these diseases is gradual, and unsuspecting growers do not realize the damage they cause.

On other hand, the injuries caused by such insects as the webworm, the walnut caterpillar, the pecan leaf case-bearer, the Japanese beetle, and others are somewhat spectacular in that the leaves may be partly or completely consumed on portions of the trees. The injury caused by the walnut aphis, the walnut lace bug, the pecan black aphis, and others, on the other hand, is less conspicuous; but the end result is far more serious than it usually is with the leaf eating insects, because the damage caused is more widespread, almost all of the leaves on a tree being affected. These sucking insects are small in size and may be overlooked until premature defoliation takes place. If nut trees are to bear satisfactory crops of well filled nuts, the diseases and insects that attack and cause injury to the leaves must be controlled. Under normal conditions the size of the crop produced, the regularity of bearing, and the quality of the nuts harvested is proportional to the leaf area of normal leaves carried by the tree from early spring until freezing-weather in the fall.

+Second growth of the trees:+ Certain of our nut trees, such as pecan and walnuts, under some conditions have two or perhaps more periods of shoot growth during the same growing season. The first, or main period of growth, starts at the time of foliation in the spring and ends soon after the shoots flower. The second period of growth, if it occurs, may begin any time after the nuts are set, and may end any time later. This second growth seriously affects the filling of the nuts, in that food materials are consumed in producing this second growth rather than in the growth and filling of the nuts. Generally this second growth is not made until late in the season, and it usually follows a period of dry weather, when conditions again become favorable for growth. Usually this is at the time the kernels should be developing, and hence the degree of filling is affected. The seriousness of the effect on the filling of the nuts is largely proportional to the amount and duration of this second growth. A third period of growth may occur later if weather conditions are suitable.

+Preceding crop:+ It has already been pointed out that nuts are storage organs and in their growth and development large amounts of food materials and minerals are removed from the tree. Under conditions of heavy crop production, the reserves of these materials left in the tree at the time of harvest are likely to be very low; and unless the trees are growing on a fertile soil and carry their leaves until frost, these reserves of minerals and elaborated food materials are not likely to be restored. Under such conditions, in the following spring the reserves are low and although there may be enough to initiate flowering and the set of nuts, they are not sufficiently high to produce well filled nuts. It is for this reason that the nuts produced in an "off crop year," even though the crop may be much lighter, may be less well filled than those produced in an "on crop year."

Such nuts as pecans, hickory nuts, and walnuts transfer large amounts of potassium from the tree itself into the shucks or hulls. The kernels of such nuts are high in nitrogen, phosphorus, and magnesium as well as in oil, which is one of the most concentrated food materials and has the highest calorie value. Nitrogen reserves in the trees are readily and rather quickly replaced if adequate amounts are applied, as this element is not fixed by the soil. This is not true of phosphorus and potassium, as they are apparently taken up by the trees much more slowly than is nitrogen. Furthermore, certain soils have a high fixing power for these elements and hence they are slowly, if at all, available.

+Insect and disease damage to the nuts:+ Certain insects and diseases attack the nuts, causing them to be poorly filled at harvest. Although these pests may destroy, or cause a certain percentage of the crop to drop before harvest, and hence serve as a thinning measure, the affected nuts remaining on the tree may not be well filled at maturity. Examples of such insects are the pecan or hickory shuck worm, the walnut husk maggot, and the codling moth. Infestations by these insects occurring before the shells of the nuts have become hard cause the nuts to drop. However, infestations taking place after the nut shells have become hard do not cause the nuts to drop. These late-infested nuts may be poorly filled because the insect larvae mine the hulls or shucks, severing the conducting tissues that transport food materials from the fruit stem or peduncle through the shuck to the kernel. The damage caused not only results in poorly filled nuts but also interferes with the natural separation of the shucks or hulls from the shells.

Examples of diseases that attack the nuts and cause them to be poorly filled at harvest are pecan scab and walnut bacteriosis. Pecan scab may also attack other species of hickory. It is the most destructive pecan disease, causing a high percentage of the nuts on highly susceptible varieties to drop prematurely and those that stick to the tree to be poorly filled at harvest. Walnut bacteriosis or blight is the most important walnut disease in the West and unless controlled causes severe losses from premature drop or from nuts both poorly filled and having discolored kernels at harvest. It is obvious that if large crops of well filled nuts are to be produced, these insects and diseases must be controlled.

+Weather conditions:+ Many growers are inclined to blame the weather for all small crops and poor nut quality because they realize it can have such important effects. In reality its direct effects are generally much less than they are thought to be, and its indirect effects are usually much greater than is usually realized. Weather conditions have a very great effect on the development of insects and diseases and on the damage caused by them, so that most often these are of major importance.

It has already been pointed out that a prolonged drought may adversely affect the size of nuts when it occurs while they are growing in size. Similarly, the degree to which nuts are filled at harvest is affected by the moisture supply during the filling period. A moisture deficiency within the tree probably affects the translocation of food materials to the nuts to a greater extent than it affects leaf functioning, for under such conditions the leaves will withdraw so much water from the developing nuts that the shucks and hulls become wilted. Under conditions of prolonged drought the kernels do not fill properly, maturity of the nuts is delayed, and the shucks or hulls do not open normally.

Under drought conditions the temperatures of the air and of surfaces exposed to the sun are often very high, and this sometimes results in sun-scald or burning of the hulls or shucks. In severe cases the injury extends through the hull or shuck to the shell and kernels. The pellicle, or skin of the kernel, turns brown or amber color, as does the portion of the kernel that has developed at the time of injury. Further development of the affected portion of the kernel is arrested; and on drying it becomes shriveled because of lack of filling. The greatest amount of damage from sunburn occurs on the south and southwest sides of the trees. Little can be done to prevent this type of injury other than to grow good, strong, vigorous trees that bear a heavy dense foliage that shades the nuts.

+Heterosis or hybrid vigor:+ The pistillate flowers of certain nut species, such as the almond, chestnuts, and filberts, must be cross-pollinated with pollen from another variety if satisfactorily crops of well filled nuts are to be produced. These species are self-sterile or self-unfruitful. On the other hand all walnut, pecan, and hickory species are self-fertile and cross-fertile, but may be self-unfruitful because of dichogamy, because they may shed their pollen either before or after the stigmas of the pistillate flowers are receptive to it. In all nut species cross-pollination is generally recommended so as to assure a set of nuts. With cross-pollination a better set of nuts is to be expected than with self-pollination, as well as better filling of the kernels. It has recently been found that when the pistillate flowers of a certain variety are cross-pollinated with a pollen from another definite variety the embryo or nut kernel is larger and better filled. This is a manifestation of hybrid vigor, or heterosis. Heterosis has been found in the chestnut and in the pecan. It likely will be found in other nut species. Some day the principles of selected and controlled parentage underlying hybrid vigor may be utilized in producing superior nuts, as these principals are now so widely used in producing hybrid seed corn.

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President Davidson: That paper was so extremely important that I hesitated very much to stop it, but we are already at the point where we should have adjourned. Now, unfortunately, we have some very important things, I think, yet before us, but if the speakers can give their talks from now on in the form of, shall we say, syntheses of the whole thing and give us the conclusions rather than the details, it will be appreciated by us all. Mr. Wilkinson is going to give us a very important talk on what he has done with the propagation of the Lamb curly walnut. Mr. Wilkinson.

The Grafted Curly Walnut as a Timber Tree

J. FORD WILKINSON, Rockport, Indiana

Our native trees are and have always been one of the most valuable resources of this country, and one of the greatest heritages ever to fall to a nation.

Wood has been used by our people since the landing of the Pilgrims, for almost every comfort and purpose in life, from the making of cradles to caskets.

Wood is still one of the principal materials in building homes and furniture, and is used for railroad ties, for paper, and in so many other ways that we could scarcely get along without wood.

The United States is the native home of many species of trees, of which a number are superior in some certain ways for some special purposes. The hickory has no equal for ax handles. As a building-timber where strength and durability are needed the oak ranks among the first. Other species are equally as important for some other uses.

Not to be overlooked are nut trees. They serve the twofold purpose of producing both food for man and wild life, and valuable timber.

+Black Walnut Has Great Value+

Of the nut tree group, the black walnut is one of the most important. It ranks among the first for lumber, furniture, cabinets, and finishing material. It has no rival in use for gun stocks and airplane propellers; as walnut wood is light, strong, will not get rough, but wears smoother with use. Neither will it splinter when pierced by a bullet. Walnut wood has been largely responsible, at times, for keeping us a nation of free people.

The black walnut tree is an aristocrat of forest and field. It can justly be proud, for no other tree can fill its place. As the late author A. H. Marks said, "Who has not noticed the look of contended usefulness which a nut-bearing tree wears? It is of use to the world and knows it."

Walnuts, like other species of trees, are not all alike, either as to nut production or in the grain of the wood.

+The Lamb Black Walnut+

Several years ago an unusually highly figured, and very valuable, black walnut tree was discovered by Mr. George N. Lamb, then Secretary-Treasurer of the American Walnut Manufacturers Association of Chicago, Illinois.

When the logs from this tree came into the mill, and their value was realized, Mr. Lamb went to the place where the tree had grown. He secured some twigs from the branches of this top and sent these, as I have been informed, to Dr. Robert T. Morris and Mr. Willard G. Bixby, knowing of their interest in propagating better varieties of nut trees.

This wood had been taken from the top many days after the tree was felled, and so was dry and nearly dead. I believe Dr. Morris succeeded in getting only one graft to grow, and Mr. Bixby two. This variety was then named in honor of Mr. Lamb.

Several years later Mr. Bixby sent me a very small stick of graft wood from one of his trees, from which I made two grafts. One of them grew, giving me a start of this variety. I have annually propagated a few trees of it ever since, though with little encouragement, and even much discouragement from others, including State and U. S. Government authorities.

On one occasion I thought I practically had an order for a quantity of these Lamb walnut trees for a reforestation project. However, the prospective purchaser, before placing his final order, wrote to government authorities, then wrote me as follows:

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" ... Sept. 30, 1940 ...

"Following some investigation in connection with the so-called curly walnut varieties, we have been advised by government authorities that these trees do not form, or grow into, a curly walnut tree at any time during the growing stage.

"We took it for granted that the wood formation would be of a curly nature, and for that reason we were interested in that particular variety.

"In view of this information which we have concerning these trees, we would not be interested in growing them as we have plenty of native black walnut here...."

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This and other discouragements, from both government authorities and individuals, had about as much effect on me as King George's advice to the American people not to use tobacco; they smoked calmly on, and I continued to propagate Lamb curly black walnut trees.

I have been propagating nut trees since 1910, and have never yet known one of my propagated nut trees to fail to carry the characteristics of the parent tree, as to habits of growth, bark, bud formation, foliage, texture of wood, or quality of nuts. The Deming Purple walnut tree, when asexually propagated, reproduces the purple wood, so I reasoned the Lamb variety would reproduce figured wood. Nature seldom blunders.

+Value of Original Lamb Walnut Tree+

When I was in Grand Rapids, Michigan, a few years ago, doing some tree work for the late William J. Wallace, he took me a few miles to the location of the original Lamb tree. It was near a small river in a gravel loam soil near Ada, Kent County, Michigan.

The following is an extract of a letter received from Mr. Lamb as to the original tree:

"November 27, 1929

Lamb Figured Walnut-- Cut into veneers @ 6 to 18c per sq. ft. (1/28") Use: Furniture Amount of veneers 60627' [Value: $8,637.62 to $10,918.86 (Prewar!)--Ed.] Logs produced: 8' x 21"--144 Log Ft. 6' x 18"-- 73 " " 10' x 36"--640 " " 14' x 30"--591 " " 10' x 32"--490 " " Stump --500 " " _____

2438

Location of tree--Ada, Kent County, Michigan. Location--River flat 20 rods from river. Soil-Gravel loam. Type of tree--Open grown. Shape---Double stump. Height--40 ft. Figure--Throughout the tree."

Mr. Lamb further states in his letter: "Unquestionably it was one of the most thoroughly figured trees ever discovered, and if figured wood will propagate itself this stock should, certainly should, do so."

He further states, "The figure in this tree was quite apparent, even in the small branches, while the Forest Products Laboratory found evidence of a developing figure in the twigs not over five years old."

The wood specimens I now have on exhibit here were taken from one of my 12-year-old grafted trees that I cut, and in them you will find figure visible to the naked eye, or easily noticeable by touching with a finger, in wood from branches not over 7 years old.

Comparing age at which figure shows in the wood of the two trees, this young tree seems to be developing figure at an early age, as in the parent tree.