Preliminary Results from Training Chinese Chestnut Trees to Different Heights of Head

J. W. Mckay and H. L. Crane[2]

Introduction

Many growers of Chinese chestnut (Castanea mollissima) want to know how soon their young trees may be expected to bear their first crops of nuts. This is determined by several factors, but perhaps one of the most important is the amount and kind of pruning the trees receive during the first four or five years they are in the orchard. One reason for the importance of type of pruning is the characteristic habit of the species to form branches low on the trunk, so that low-headed and spreading tops result if trees are left unpruned.

It has long been accepted by most horticulturists that any kind of pruning of fruit trees tends to be a dwarfing process. Hence, pruned trees would be smaller than similar unpruned trees. Pruning of young fruit trees, though reducing the size of the top and the number of growing points, tends to stimulate the growth of the remaining shoots. This has a marked tendency to delay the formation of fruit buds. Hence, unpruned trees come into bearing earlier than even lightly pruned trees. Tufts (2)[3] reported that lightly pruned deciduous fruit trees, such as apple, pear, apricot, and peach, came into bearing one to three years earlier than similar trees that had been heavily pruned. Crane (1) found that height of head in apple trees had little effect on yield for the first nine years in the orchard, but at the time the experiment was terminated the trees were still too young for him to expect much fruit production. He found, however, that the low-headed trees made more shoot growth and a larger gain in trunk diameter than the high-headed ones, and thus the bearing area was larger. Because the tree form of the horticultural varieties of Chinese chestnut is somewhat comparable to that of apple varieties, it would be expected that the two might give similar growth and yield responses to pruning or training procedures. The experiment described in this paper was initiated for the purpose of determining the response made by trees of Chinese chestnut varieties pruned and trained to three heights of head.

Experimental Procedure

The three varieties used in the experiment are Meiling, Nanking, and an unnamed variety carried under the accession number 7916. The last variety is characterized by dwarf, heavy-bearing trees that mature their crops very early in the fall, whereas Meiling and Nanking are vigorous, fast-growing varieties that mature their nuts in midseason. In the early spring of 1948 thirty-six two-year-old grafted trees were planted 25 feet apart in the orchard in four short rows of nine trees each. The three treatments consisted of (1) no pruning; (2) pruning to a 2-foot head; and (3) pruning to a 4-foot head. Three trees, one of each variety, were included in a plot or treatment. Thus, the experiment was arranged in a randomized block design with the three treatments randomized in each row and the four rows serving as replications. Each spring the trees received a liberal application of a 10-6-5 fertilizer. Strips six to eight feet wide on each side of the contoured rows received frequent cultivation each growing season, while strips of orchard grass sod were left between the rows to prevent erosion. The soil is Riverdale (tentative series) sandy loam that had been in orchard grass sod for ten years before the experiment was begun. It has been necessary to spray the trees each year with DDT, parathion, or both to control Japanese beetles and mites.

Pruning of the trees was begun during the first winter following the planting in the orchard, but only a few of the lower limbs were removed in order not to dwarf the pruned trees severely. The second winter a few more lower limbs were removed and at this time the two-foot-head treatments were complete. A third pruning was necessary before the heads of the trees in treatment three could be raised to four feet. Detailed records and measurements were made of the diameter of each tree trunk one foot above the ground, and of the weight and number of nuts produced (yield).

Experimental Results

Table 1. Effects of training to different heights of head on the average diameter of tree trunk and yield of nuts of three varieties of Chinese chestnuts at the end of the third season (1950) after transplanting

Treatment Average diameter of tree trunk (millimeters) Yield of nuts (pounds) Number of nuts

Meiling No. 7916 Nanking Tree average Meiling No. 7916 Nanking Tree average Meiling No. 7916 Nanking Tree average

No pruning 43 43* 47 45 .19 .43* .05 .16 11 22* 2 10

2-foot heads 25 19 21 22 0 .12 0 .04 0 7 0 2

4-foot heads 27 22 25 25 0 .03 0 .01 1 4 0 2

[*] 2 trees missing.

Data on the diameters of the tree trunks and yields of nuts at the end of the third year in the orchard are given in table 1. It should be pointed out first that these grafted trees produced some nuts the third growing season they were in the orchard. This is very much earlier than seedling trees ordinarily could be expected to bear nuts. It will be noted that trees of Number 7916 developed a somewhat smaller trunk on the average than the other varieties did, but Number 7916 outyielded them about two to one, both in weight and in number of nuts produced. The tendency of Number 7916 to bear nuts earlier and on smaller trees than other varieties may prove to be a valuable characteristic that will justify naming and releasing this clone as a new variety. The fact that it matures its nuts early may also make it suitable for growing in more northerly areas than other varieties, because the length of season required for maturing the crop presumably is shorter than for other varieties. However, this cannot be determined without extensive tests in the North, which are now being made by a number of growers.

It will be noted also in table 1 that the trunk diameters of the unpruned trees were about twice as great as were those of trees trained to two-and four-foot heads; and furthermore, the yield of nuts was more than four times as great. This means that cutting off the limbs that formed below the 2-foot level checked growth so that the bearing surface of the tops was greatly reduced as compared with that of unpruned trees. Also, growth of the tops of these trees was etiolated and spindly, and the shoots produced few or no catkins as compared with the abundant catkins produced by the unpruned trees. Several of the trees with four-foot heads became so top-heavy that staking was necessary, and nearly all the pruned trees leaned to some extent. At the end of the third year in the orchard, the unpruned trees were much taller than trees headed at two and four feet, and the spread of branches was also much greater. Preliminary results from this experiment indicate that early pruning of young Chinese chestnut trees causes severe dwarfing and consequent delay in the formation of catkins and the bearing of nuts. All pruning operations should, therefore, be delayed until the trees reach bearing age, and from that time on low limbs may be removed gradually from year to year until the trees are trained to the proper height.

Literature Cited

(1) Crane, H. L. The effect of height of head on young apple tree growth and yield West Virginia Agr. Exp. Sta. Bul. 214. 1928 (2) Tufts, Warren P. Pruning young deciduous fruit trees California Agr. Exp. Sta. Bull. 313: 111-153. 1919

Discussion

MR. McDANIEL: What age and height were these trees when planted?

DR. McKAY: These trees were grafted on two year old stock and allowed to grow a year. They were three years old. They have grown in the orchard three years, so they are now six years old and about five feet high.

They were grafted about a foot from the ground and they grew three feet or so. They were a good size grafted tree.

MEMBER: May I ask the time of the year when you pruned?

DR. McKAY: In the dormant season.

MR. SHERMAN: I have been pruning some Persian walnuts. Just as the side branch starts I rub that bud off and I can't see that I am dwarfing it any.

MEMBER: Maybe you aren't pruning enough to do any dwarfing. We have removed whole limbs.

MEMBER: I have taken it off and allowed the center to go up.

DR. McKAY: It may have different effects. We actually removed wood from the tree.

MEMBER: Is that 7916 a pretty good sized nut?

DR. McKAY: It is a smaller nut. The 7916 is a potentially high bearer. It bears quickly after it is planted and that is one of the things a lot of us are interested in.

MEMBER: How about eating quality?

DR. McKAY: It is just as good.

Our preliminary conclusion is that early pruning in this species causes severe dwarfing and delay in the fruiting of Chinese chestnuts. Just let them alone. Plant them and forget about pruning them until they come into bearing. Let them alone and you will get nuts two or three years sooner than if you start taking those lower limbs off. Once you get it into bearing then start in and take off a few limbs on the bottom. You could still over-do the thing. The point is to wait at least three or four years. We will have some recommendations in another year when we shall know more ourselves.

MEMBER: What do you disinfect those cuts with?

DR. McKAY: We don't figure it is necessary to be too particular about painting the wounds. Those wounds heal over very quickly. Use an asphalt tree wound compound.

MR. SILVIS: Personally it appears to me that Walter Sherman's method of rubbing off the buds or very young shoots just as they start growth is to be preferred. Your method of cutting off limbs is destructive pruning. Though you say pruning dwarfs the tree, actually the root is still there and given enough time will not the tree recover?

DR. CRANE: I carried on pruning experiments for many, many years, with apples, peaches, pears and cherries. Since then I have been working on nut trees. As for this debudding, the reason he doesn't know he was injuring, was that he didn't have checks and experiments. When you have, you will see that debudding or even pinching the terminals will actually dwarf the tree, although not as badly if it is not done in the summer time. If you do it in the springtime, and if you keep on debudding along in June and July, you are dwarfing your trees.

MR. McDANIEL: In the University orchard you will see some Chinese chestnuts which have been pruned heavily, and the results aren't good.

MR. CORSAN: I visited a sweet chestnut orchard in Michigan, and the grower told me that there were two types of Chinese chestnut trees, one that grew tall and the other squatty. The one that grew shorter was much later than the tall one. Then I would like to tell you about an experience I had years ago. I imported from this state of Illinois from Miss Amelia Riehl, and I also planted about a bushel of seed of Chinese chestnut trees grown in the Niagara district. These Niagara seedlings are quite large and the amazing thing is they didn't grow any nuts. So I came across another orchard in the Niagara district where they were growing that large pointed type of nut and I got some grafts from that and I put them on these non-bearing trees and they all took at once. A bunch of them would all grow up without any failure. That was easy and now they are growing fine. I just thought I would tell you that peculiar experience, and that knocked me cold. The trees from Illinois and the trees from the seeds of the large good sized nuts were equally good.

MEMBER: Did they bear after you grafted them?

MR. CORSAN: They sent out sprouts that far. [Indicating.] The trees were all right.

MR. STOKE: I think you are both wrong. I think you will take the tree and plant it without pruning and then it starts and then in the summer after it is in full leaf pinch off the leader in the lower branches. That will retain the value of those lower leaves. By doing that and suppressing the lower you will get better results than either of the other ways. Nature will remove and make unfruitful the lower ones. You can help nature in forcing the upper growth and removing the lower.

DR. McKAY: That is one way of doing it. A lot of people want to get ahead of nature. If you wait for those lower limbs to die, the tree will have to be pretty large. Lots of people want to get under their trees before that. You sometimes want to get there after three or four years. I think it would take ten years for the shade to do it.

MR. STOKE: I didn't mean to let the shade do it. We after three or four years can remove the limbs ourselves with less shock and much better results. That will work on any tree.

DR. McKAY: I don't see how you can remove.

MEMBER: You force stronger leaders at the top and hasten the growth of the top.

MEMBER. You will get a delay of fruiting.

MEMBER: I think you make up for it.

DR. CRANE: That may be true. We have seen very conclusively that when you prune even a little you are going to destroy fruiting.

MR. STOKE: You will have a larger tree in five years by my method than by yours.

MR. A. M. WHITFORD: I have trees of that very spreading type of Chinese chestnut, that are lying on the ground and I should have removed those limbs five or eight years ago. You should remove them in not more than five years after planting.

DR. McKAY: I want to make a comment. Some grafted trees are not bearing. This to us shows the importance of varieties. This difference between 7916 and the two others is so striking it means in the future we have to pay more attention to the varieties. There is no question that some varieties will bear sooner than others. We have to talk about grafted trees because that is the only thing that can be developed. Every grafted tree is potentially like every other of the same variety.

MEMBER: What factors suppress them? In pinching back, do you mean that the actual growth rate is changed, or that debudding will suppress the entire tree?

DR. McKAY: We mean the amount of the top itself. Usually it is the spread and the height together. When you prune, you tend to hold back the total amount of the fruiting area of the tree. If you allow it to develop untouched you have a greater fruiting area.

MEMBER: The chestnut tree often will sprout from the trunk. What are the processes to check that?

DR. CRANE: It is very largely root pressure. When you have a tree that is uninjured, all of your water and soluble minerals are going up to the top. When you have the tree trunk killed or cut off you still have water in your root system. In some trees you have a lot of adventitious buds that are still there and never forced out. Nitrogen will force those dormant buds into growth. At each walnut node or leaf we have as many as seven buds, all of which are capable of producing growth. Normally it is only the major bud that grows, but propagators sometimes get a patch bud back to life even though the primary bud dries up. Keep on forcing it and you are bound to get a sprout out of that bud. That is just the way it is with a lot of dormant buds. There are so many that when we cut off the top these dormant buds are forced into growth. Some trees don't have them. Tung does not form dormant buds, but will form those adventitious buds. They will form numerous buds even in a very small area of callus. It is just a safeguard that some plants have developed to keep the individuals alive.

MR. McDANIEL: I think what Mr. Craig had in mind was the tendency there is in Chinese chestnut to form multiple trunks.

DR. CRANE: That is due to these dormant buds and the ability to produce callus. Chestnut is one of the species that produces abundant callus very readily. That is one of the reasons this Chinese chestnut is so blight resistant. When it has an injury it will form callus at the point of the injury.

MEMBER: Would you tell me how you would start a blind bud growing. It will not break. It doesn't form. When I come to a wood which is blind I cut it off.

MR. CHASE: We have had such buds and find if that bud is blind you can force all you want to but you won't get any new buds to grow from that bud patch.

DR. McKAY: It does on two-year wood. Perhaps on one-year wood you have no adventitious buds. When the bud dies, that patch is through. On two-year wood frequently small adventitious buds will grow.

MEMBER: If you rub the main bud off, it will start on the side.

MEMBER: Do you recommend two year wood for budding?

DR. McKAY: We recommend one year if it is large and vigorous. If you have to use chestnut wood smaller than a pencil the results will be indifferent.

MEMBER: What time do you recommend budding?

DR. McKAY: We graft in spring, the first week in May, using dormant wood the size of your little finger. We wait until the first leaves are open, usually in May.

MEMBER: Do I understand that most any place along that tree trunk there are adventitious buds?

DR. McKAY: Particularly next to the root.

MEMBER: Have you had any success in bench grafting of the chestnuts?

DR. McKAY: We have had some success and other times failures. We can't recommend bench grafting. Perhaps you can do it, but we haven't yet worked out a satisfactory method.

MEMBER: Wouldn't it do better if you dipped the top in paraffin or something?

DR. McKAY: Ask Mr. Bernath. He is the authority.

MR. BERNATH: No, none whatever. No, it wouldn't help.

MR. CORSAN: In New York they had weevils. That is the most terrible thing I ever saw. Has the weevil disappeared entirely?

MEMBER: No, indeed, we have weevils over a large area. It is a very important pest in the East and in the Ozark Chinkapin range around chestnut plantings. There is a very satisfactory and easy way of control. DDT, two pounds per 100 gallons of spray solution or a dust of one per cent. The trees are sprayed once or twice or three times from about the last of August on until shortly before harvest.

MR. McDANIEL: That is discussed in last year's annual report.

MR. CORSAN: I fumigated my seed nuts for the weevils and killed them all effectively, and we have no weevils of hickory or chestnuts now. That is, as far as southern Canada is concerned. It would matter terribly if we had any weevils of any kind. Anyone hear about the hickory and chestnut weevil?

MEMBER: Standard directions are available for the control of weevils both in chestnut and hickories.

MEMBER: There are practically no weevils in New York. The boundary line would be about southern New Jersey. It doesn't make much progress farther north. It's also absent toward the Southeastern and Gulf coasts.

MEMBER: That is an interesting discussion, but it is off the current subject.

DR. ROHRBACHER: I am sure your project is interesting, manifested by the questions you have been asked.

FOOTNOTES: