THE DISEASES OF NUT TREES

M. B. Waite, Washington, D. C.

In taking up the question of nut diseases it is hardly proper, perhaps, to take too narrow a view of it and I will, therefore, mention some of the other work being done here in Washington that is of interest to the Northern Nut Growers Association.

You all know of the pomological work being done on nuts, and I hardly need mention the work now being carried on by Mr. C. A. Reed, a member of this association. It might be well to remind you that the work was started by Mr. Van Deman some twenty-five years ago, and continued by Mr. Corsa, and a report was issued some fifteen years ago. It was taken up later by Mr. William A. Taylor.

The plant introduction work of Mr. D. G. Fairchild should be mentioned. He is scouring the world for new nuts of all kinds for the northern and southern, eastern and western United States, and introducing them into this country. The diseases of those nuts are studied by Mr. Orton in the Cotton Truck Division of our department.

Outside of the Bureau of Plant Industry also there is some work being done on nut trees. The insects attacking cultivated nuts are studied by Professor A. L. Quaintance, of the Bureau of Entomology, along with the deciduous fruit insects. The insects attacking forest nut trees are studied by Dr. Hopkins of the same Bureau in the laboratory that studies the forest insects. Of course the nut trees, as forest trees, are studied in the Forest Service about which you all know.

One thing more that I would like to say, in way of explanation or apology, is in regard to criticism of the Department for not more thoroughly attacking the filbert blight. Only forty-five thousand dollars are appropriated by Congress for the investigation of the entire fruit disease problem of the United States. That includes the great citrus industry; everything, in fact, from cranberries on Cape Cod and the mouth of the Columbia River to grape fruit in Florida or apples in New York. It includes the subject of all the nut diseases, and that means the problem of the diseases of the pecan, of walnut bacteriosis—that is a big problem—in southern California, and more or less in other parts of California, our great apple industry, the peach yellows, the pear blight, etc. When it comes to parceling that out it only leaves about three thousand dollars for nut diseases, and thirty-five hundred dollars for studying diseases of citrus fruits, so you must not be surprised that we cannot put a group of men on this problem and study it as it should be studied. It is a question of men and means.

Perhaps now some general information might be of interest and set you to thinking.

In the first place in every disease problem, conspicuously so with our fruit and nut diseases, there are two main classes of plants to be considered, our native plants and the foreign plants. The pathologist is always looking to the native origin of a plant in studying its adaptation to the environment in which it is attempted to be grown. A foreign plant may not necessarily be unadapted to another locality. The vinifera grape is thoroughly adapted to California and to much of the Pacific slope beyond the Rocky Mountains, but you know the vinifera grape has a hard struggle in other parts of the United States. This is not only a pathological problem but a physiological one. It cannot stand a soaking rain for two weeks at a time; it cannot stand so much water and humidity but it wants dry, hot sunshine continuously from the time it puts out its leaves in the spring.

Another phase still more interesting is the question of foreign parasites. Many of the worst diseases with which we have to contend are either native diseases attacking introduced plants, or foreign diseases attacking native plants. I will take that up in detail. Nature has fought the battle all out with the native parasites against the native host plants, so we don't have to do it. It's a case of the survival of the fittest. They have won, so when we are dealing with native plants against our native diseases, we have a condition that has been fought out in nature for nobody knows how many thousand years. The result is that unless we disturb the balance too much by cultivating great orchards of a thing that has been grown as scattered individuals, or overforcing it or selecting and breeding towards larger fruit without any regard to foliage and other characters we can go ahead with our breeding and selection and cultivation and trust nature to keep the balance to some extent. We have this natural balance in our favor in dealing with the problem of cultivating native plants. As an example take the pear and apple blight. The pear blight problem is one in which a native parasite on wild crab apples, which occasionally kills a few twigs here and there, attacks the juicy, tender, susceptible, introduced European pear and makes a very serious disease. It is a fight indeed to grow it in so much of the country that pear culture has been very largely suppressed over the eastern half of the United States and part of the Pacific coast. All this trouble has been caused by one little native microbe. Apple culture also, with certain varieties, has been seriously interfered with in some sections.

The apple cedar rust is probably the most striking example of a native parasite attacking a foreign host that we know of, and particularly so as the remarkable evolution in which the parasite has adjusted itself to the new host is taking place right now every year. The apple cedar rust is becoming a more difficult problem clear across the eastern United States to Nebraska. It has occurred as a serious disease since 1905 to 1907. As a botanical curiosity we have known it a long time, but as a serious disease, it is very recent, and nobody knows yet how serious it is going to be.

We have a very striking example of this introduction of a foreign plant and the plant being attacked by a native parasite, in the case of the filbert blight, and I am going to take that up later. The trouble is that we have brought into the United States a European filbert and it has been attacked by a parasite of our wild hazelnuts. The disease is very rare and is seldom seen on the wild hazelnut,—so rare that it was hardly known by scientific botanists, and yet it interferes with filbert culture in the eastern United States and is the one thing more than anything else to make filbert culture unprofitable. We have practically the same proposition in the walnut bacteriosis, not only in the northeastern United States, but in the best walnut districts of California. This bacterial disease which is undoubtedly a disease of our native walnuts—probably the native black walnut—occurs rather rarely, and so feebly developed as to be difficult to find at all on its native host yet it becomes the great serious disease of the Old World cultivated walnut.

Now, there again, it is not so much a lack of physiological adaptability, because the walnut is thoroughly adapted to our Pacific coast. I suppose most of you know that east of the Rocky Mountains, east of the Great Plains, we have a humid climate and winters more or less cold which corresponds, not with western Europe, not with Germany, England, Spain, France and Italy, but with China and Japan, with Asia, in its climatic conditions. The result is the Chinese and Japanese trees brought to the eastern United States grow well but may grow indifferently in California. On the other hand, the plants of the Mediterranean, France, Germany, Italy and Spain do not, as a rule, thrive when introduced into the eastern United States. There are a few exceptions, like the apple and perhaps the peach. These are not really natives of western Europe, but have been brought from the interior. They are more like the Japanese and Chinese plants which came in by way of Persia and which have been slowly adjusted to the conditions of western Europe. That adjustment has gone so far that the Persian type of peach does better on the Pacific coast than in the East. We are breeding a race of these fruits from China, the Chinese cling group, which does well in the eastern part of the United States, and we have from there a peach that is better for the country east of the Rocky Mountains than the ones that have been modified in Europe.

Now take the other side of this question, the foreign parasite—that is very unfortunate thing—over which we do not always have the control that we do with the foreign host. An equal disturbance of nature takes place when we introduce a foreign parasite, whether it is from a similar climatic region or one not so similar. The chestnut blight is a tremendous example of that sort of thing. This has come into prominence within a decade and it is one of the greatest problems in the pathology of the chestnut. That has turned out to be a Chinese parasite. It was found last summer by the agricultural explorer, Mr. Myers, but the fungus was studied out by Dr. Shear.

The three great American parasites of our native grapes are the black rot, the downy mildew and the Phylloxera, an insect pest, and they caused a great amount of study and work and investigation and great expense when they were introduced into France and South Germany and Italian vineyards, and were fought out only by what might be considered a magnificent effort on the part of the European governments, especially France. On our native wild grapes those diseases are almost trivial, and the wild seedlings in the woods are practically immune, but when we cultivate them and select the tenderer varieties, the black rot is pretty bad, especially on the Concord, and particularly when that is hybridized with grapes of European blood. Nevertheless, we have cultivated them in order to get the large juicy fruits. There are many more examples of this sort.

Now about the cultivated nuts. I wish I could tell you how much I think of the native nuts. I grew up in Northern Illinois and could go out on a day like this and gather two or three bushels of hickory nuts. How I enjoyed the black walnut, especially when it was just shriveled so it would leave the shell—it got rather too rich when it was dried and stale in the winter time—but how delicious it was when just wilted! Also there was the butternut and the wild hazelnut. I used to take a one-horse wagon into the woods on a Saturday and gather enough hazelnuts in the shucks to fill it; then we had hazelnuts all winter. So I am in full sympathy with the Northern Nut Growers Association and I would like to see those nuts grown, if not wild in the woods, at least in cultivation.

There might be a few things of interest to you about the wild hickory nut. According to Farlow's Index of North American fungi of twenty-five years ago, there have been thirty-seven species of fungi collected on that tree. Probably there are twice that number as a matter of fact, but mycologists have collected, described and named thirty-seven species on the Hickoria ovata, the plain shagbark, and the other hickories have similar numbers. The pecan has only three named species in Farlow's Index, but Mr. Rand has got together three times as many I think—I am not sure of the number.

Of the pecan diseases, the pecan scab is probably the most conspicuous fungus trouble. The pecan scab is the most typical fungus parasite of the pecan. It attacks the leaves, fruit, etc. It attacks the vessels or veins of the leaves and frequently enters by means of aphis punctures which break the skin so that there is no doubt but that this particular disease is favored by an aphis. We have investigated this disease quite carefully and carried on a series of spraying experiments for some three years and there is no doubt about our ability to control it. It can be prevented by spraying with Bordeaux mixture. You never can tell how many sprayings will be required. It may take three to ten sprayings to protect the nuts. The leaves are grown mostly within a month—the leaves are pushed out within thirty days and you can spray those leaves and protect them. The weak point in the treatment is that the nut of the pecan grows steadily from the time it starts to way into September. This makes a hard problem in spraying as the nut keeps expanding and forming a new and unprotected surface for an unreasonably long season and they are susceptible to scab attacks all the time, so you have the problem of spraying the nuts all summer. The spray does not stick very well on the nuts. The result is that we advise dodging that parasite by planting the non-susceptible kinds; it is much better and cheaper. It is certainly an encouraging thing that you can plant good varieties, that do not scab badly, and which at the very most require but two or three sprayings to protect them entirely, and in a great majority of cases, no spraying at all. Those already are the great nuts in cultivation, like the Stuart, the Schley and the Frotscher. Most of those good varieties will be occasionally attacked by scab because of a wet season, just as a variety of apple which is very resistant to apple scab is occasionally attacked by that disease.

The pecan has quite a number of leaf-spot fungi and most of those we have tested by spraying. These experiments have been made in the nursery where it is more convenient to spray and where the necessity is, perhaps, a little more pronounced, and there it is, undoubtedly, a proper practice to spray and fight out the pecan leaf diseases. Bordeaux mixture is the thing to be used on all occasions. The pecan resists copper poisoning almost as well as the grape and can be sprayed with safety.

If a pecan tree has crown gall don't plant it. All nursery trees should be rejected in planting if they show signs of this disease. The pecan has fungus root-rot and various wood rot fungi besides the leaf diseases. It also has several other troubles more or less serious. Occasionally in the pecan groves you will find these remarkably white mildewed nuts. That gives way to spraying. Another disease is an internal spot on the kernel which Mr. Rand has been working on and which seems to be due to a fungus. We don't know how to prevent that yet. The pecan has a fungus attacking it that is very similar to the bitter rot of the apple. The pecan anthracnose looks like the bitter rot, has the same pink spore masses and you will be able to recognize it. That may be prevented by spraying, but it is, fortunately, not a serious disease. The northern nut grower will not have so much trouble with that, as it is a southern disease. Here is a physiological trouble that causes blackening of the young nuts on the inside. It appears to me to be due mainly to wet weather, but I don't know its exact nature. It came primarily on a pecan raised in the semi-arid section of Texas and brought into South Carolina, and by the way you can get as much trouble in adapting trees from the western to the eastern United States as in bringing in trees from other countries. In parts of semi-arid Texas the trees are supplied with moisture by sub-irrigation and when we move those pecans to the humid East we get almost as much non-adjustment as when we bring in foreign things. I would suggest that these pecans from western Texas are the very ones to take to Utah and California rather than those from the eastern part of the United States. They are adjusted to dry seasons with moisture at their roots and you will get the best results from them when grown under irrigation.

I will now take up the walnut, Juglans nigra, the common black walnut. There are twenty species of fungi which are known to attack it. Quite a good many of these attack the twigs and cause them to die, and probably half are leaf diseases. One, commonly called white rust, a disease of the leaves, attracts mycologists in collecting, but it has never been of serious economic importance.

Now, as to the butternut, Juglans cinerea. It has about nineteen species of fungi known to attack it, but probably many more will be found when the nut is thoroughly studied.

Juglans regia, the cultivated Persian walnut, has only about twelve species of fungi recorded from it in this country. There are, undoubtedly, more to be found. Of these fungi the walnut bacteriosis, caused by a bacterial germ is more important than all the rest of the parasites put together we can easily say. The California walnut bacteriosis has turned up at various points in the East. The twig blight form of this disease is also prevalent in various states. The walnut blight or bacteriosis is therefore to be figured with in planting the Persian walnut in the East.

Professor Smith: Is it worse or better here than in California?

Professor Waite: There have not been enough walnuts grown here in groves to allow the disease to accumulate—to have a fair test for that, Professor Smith. I don't believe we know; but it is, undoubtedly, a parasite of our native black walnuts. It occurs in Texas and Louisiana, and I think we have it in or near Buffalo, N. Y., and in New Jersey, so if I were planting extensively I should expect that disease to be serious. That would be my forecast of the matter. The humidity and the cloudy weather in the East ought to be more favorable to the disease than the climate of California.

Mr. Jones: For that reason I should think the disease would work fast in the Gulf Coast.

Professor Waite: Yes, those specimens of yours seem to show a very serious condition.

We must not pass over the chestnut without noting that there are thirty species of fungi attacking it, and that does not include the new one, the bad one, the chestnut bark disease.

The filbert blight belongs with the diseases of the European grape and sweet cherry. The filbert is an example of a European plant introduced into the eastern United States attacked by a native parasite which almost drives it out of cultivation. In fact, there are so few filberts in cultivation even now that if we were trying to plan a spraying experiment on them we would not know where to find a plantation suitable for carrying on the experiment. If any of you know of any such plantations I would like you to let me know about them.

The Chairman: We will have some in two or three years.

Professor Waite: Here is a sample of the filbert fungus taken from our pathological collection. It shows the mature fruiting bodies of the fungus and it also shows that the twigs are killed. This fungus is known as Cryptosporella anomala. It was described as Diatrype anomala by Peck of Albany, N. Y., but was afterwards found to belong to another genus. There have been two or three articles published on it, the best one probably by Humphrey in Massachusetts. I have an abstract of that which can be copied in the proceedings, if you wish.

(See Appendix.)

The fact that this Cryptosporella is related to the black knot of the plum is an interesting feature; and that it attacks the growing canes during the growing season and fruit during the fall and winter. He suggests the treatment of removing all the infected branches during the fall and winter. I would add to that, complete eradication of all diseased branches of the host, and they are rather easily seen, in the fall as soon as the leaves are off—then a thorough spraying with strong Bordeaux mixture, at least 5-5-50, preferably stronger than that, of course burning all the material that you cut out. One is at a disadvantage if there are wild hazelnuts in the neighborhood. How to handle that problem I am hardly prepared to state; perhaps, by eradication of the wild hazelnut in the vicinity.

The Secretary: I think that would be impossible in most regions.

Professor Waite: Mr. Kerr had his growing on the eastern shore on an island where there are no wild hazelnuts and they were not attacked by the fungus.

A Member: They are all dead now.

Professor Waite: The number of sprayings during a season is an undetermined question. It will be necessary, probably, to spray two or three times. You can certainly protect the two-year wood in that way by making a fall spraying and a spring spraying. This will keep them thoroughly covered with Bordeaux mixture but whether or not three or four sprayings are necessary remains to be tested.

The Chairman: Are any varieties of European hazels immune?

Professor Waite: I have not studied them enough to answer that question. I don't know. They all seem to go down. Perhaps Dr. Deming can answer.

The Secretary: I don't know.

Professor Waite: I think that is all I want to say, except one thing, and that is about the physiological aspect of these, diseases. I touched upon that phase in discussing the matter of environment in the introduction of foreigners to places where they are not adapted. In some particular seasons and circumstances even the native trees suffer. One type of injury which has caused great trouble with the English walnuts and pecans, and also with apple trees and has also caused trouble with our native red oaks, is freezing when the trees are in a non-resistant condition. There is an example of this within three minutes' walk of this building. Here are the climatic and temperature conditions that bring about disaster, particularly if preceded by a dry season. Let us start with a dry season. The season of 1911 was conspicuously dry in this locality and the adjacent states of Virginia, West Virginia and Maryland, but about the first of September the rains came. Up to that time even the native forest trees such as oaks and chestnuts showed the stress of lack of moisture very seriously and were somewhat yellow and pale looking, mainly from water and nitrogen starvation. When the rains came the wilted trees all greened up, every tree in the parks brightened up, and we had fine growing conditions until October and no cold weather up to New Year's. It was warm that fall and even on New Year's day the warmth was noticeable. On the 12th of January we had the record cold temperature for this locality in the history of the weather bureau, except one year. We had fifteen or seventeen below zero and it was as low as thirty-eight in low spots in the Potomac Valley in West Virginia. Those trees had never been fully shocked into winter conditions. The cambium growth and sap flow had not been stopped and the physiological changes needed to get the trees ready for cold weather had never occurred. They were not ready, not only as to the bark, but in the trunk and wood. The result was that the trees were seriously injured, the less matured twigs died back, and the trees were frozen on the trunks down to the ground line. In the freeze of 1904 in New York I was surprised to find that the peach trees were not all killed. They were frozen through and through and yet the trees did not die. The question of winter injury hinges not alone on low temperature, but it also depends on the condition which the tree has reached when the cold strikes it. Now, to tell you still further about what that cold wave did, I will ask you to look at that row of red oaks near the Smithsonian which I just alluded to and see the big ribs of dead bark where the cambium layer has been shocked, and checked in other places. You will find these trees ribbed and ridged to about half way down the row. Those trees are subject to special disadvantages; they lack subsoil drainage and they have an excess of manure draining down through the paving stones. They have an excess of nitrogen and lack of drainage. The subsoil is a heavy clay. That brings up another thing that I want you to notice in regard to winter injury. Plant not only hardy varieties, but select localities with good subsoil drainage. The walnuts and hickories, belonging to the two great families of juglans, and the oaks and chestnuts, want good subsoil drainage. Where the underlying rocks are vertical the conditions are ideal. They do not like a heavy clay subsoil, but do best where water and excess nitrogen can get away.

The general summary I want to make is this: Nut trees have a large number of fungus parasites. In a few cases the native fungus parasites attack European or Old World species and varieties to such an extent as to make very serious problems, so much so that they can not be regarded as solved, the walnut bacteriorosis and filbert blight being examples of these. On the other hand, most of the native fungus parasites of our native trees are not to be feared as enemies of these trees, not only in the northeastern United States where this body is endeavoring to further a good cause, but over the whole eastern United States. These parasites in some cases may be serious enough to justify spraying and other lines of treatment, especially in the nursery. On the other hand, considering the nature of nut trees and considering the results of work on the pecan scab, the object of the nut grower should be to breed and select as far as possible resistant sorts, to work on and select native species and hybrids particularly where the native trees will give the necessary hardiness, immunity and resistance. The outlook, therefore, is promising for the cultivated varieties of hickory nuts and walnuts that I know you are all working for. Foreign parasites are always dangerous. This chestnut blight fungus comes into any such scheme as that like a bombshell. When it comes to an introduced parasite like that we can not tell what will happen. I thank you for your attention.

The Chairman: I think everybody here will agree with me, when you come to look over this list of amounts appropriated for work in nut culture investigation, that there will be no further criticism of the Department of Agriculture from any member of the association for not doing more in the interests of the nut grower.

The Secretary: We are all indebted to Professor Waite for his clear way of stating facts, for resisting the temptation to give a technical talk and for enunciating principles of wide applicability.

This question of the blight on the hazel is a most important one for the northern nut growers. Mr. Reed was telling me yesterday about a man from California who went out near some city there and bought 10 acres of land at six hundred dollars an acre, planted almonds and in a few years had the place paid for and was making a good income, two or three thousand dollars a year from his ten acres of almonds. We can do almost that in the East, I believe, if we can cultivate the European hazel. If it were not for this blight, we could have splendid crops of the hazel. If the government would grant larger appropriations for nut culture investigations it might enable us to find a way to control this disease. Dr. Morris is breeding hazels, however, and hopes to get one which will be immune.

Professor Smith: It is a great pleasure to listen to a man who knows what he is talking about. I figured out some years ago that I was going to be a teacher and I decided that I would like to have a chestnut farm also. I got along very nicely, planted my trees and then the chestnut blight came along, and I regard the business, at least as to profits, as in abeyance. We are in a period of particular danger from the importation of foreign plants; we are bringing in perfectly innocent-looking things from other countries which are causing us great damage. I want to suggest to any one here who wants to plant an orchard, to plant two kinds of trees. If my nut orchard had been planted with something besides chestnuts, I would now have that something else. I would suggest the possibility of having two things on the same ground—say chestnuts and English walnuts—so if the planter finds he cannot raise one he can still have the other. Then he will not be in the same place I am with my chestnuts.

The Chairman: I understand we have Mr. Fullerton of Long Island here, and we would be pleased to have him give us some of his experiences.

DR. WILLIAM CHAMPION DEMING Secretary-Treasurer of the Northern Nut Growers Association

Mr. Fullerton: I just came in to see what you folks are doing and I don't think I can pose as a nut expert. I live on an island that has a great many varieties of nuts on it that have become native. We have quite a plantation of hazelnuts; nobody knows who planted them. They are used by nurserymen to fill orders. Also quite a plantation of magnolias which came from the South a couple of hundred years ago. They are thoroughly acclimated. We have also some of the very largest—and I am going to catch it here because I have never used a tape line—we have some of the very largest and oldest of the Persian walnuts in the United States, which produce annually a big crop of the so-called "English" walnuts. The trees produce the largest walnut I have ever seen, with the thinnest shell. They have been there about one hundred and fifty, two hundred and fifty or three hundred years. They are very large, larger than the black walnuts. Whether they were planted or not I don't know. Their history is probably this: Long Island was a sea-faring community a few hundred years ago. These sailors who went out from the island, some of them, loved nuts and they would bring back from other countries nuts or other plants, and now we have a most remarkable mess of trees. We have planted the Japanese walnut, I don't pretend to know which variety, and it began yielding the third year and has yielded every year since, bearing nuts in bunches like grapes.

The Chairman: Is it a heart-shaped nut?

Mr. Fullerton: Yes. We have some pecans and some almonds. Against the advice of everybody we planted some almond trees; they started to bear in their third year. The trees are one solid mass of glorious big red blossoms every spring. They bear very heavily and have for three distinct seasons. Hard winter or easy winter, nothing has affected their bloom and they have never had a particle of San José scale until this year. The almond grows all over the island. Also the pecan. I planted five varieties of pecans and they are still living and growing very slowly. They have been moved three or four times. Last year we planted seven varieties including the Van Deman and the Stuart and one Indiana variety. One of these trees died and the others were killed back, but they have sent up big shoots.

Two years ago an old fellow came up from the middle of the island to see if our pecan trees were the same kind as his. His story was very remarkable. He didn't know anything about trees. He went into town one day and got interested in pecans and bought all the different kinds he could find, all the different shapes. He didn't care what they were—didn't care whether they came from Canada or Mexico—he was the kind of a man who would plant bananas,—and he planted all those pecans and he told me that every one of them grew. He said they all produced nuts.

Mr. Pomeroy: The first Persian walnut nursery ever established in the United States was at Flushing, Long Island.

The Secretary: I should like to ask how old and how big are the pecan trees that are bearing?

Mr. Fullerton: I think he said seven or eight years.

The Chairman: The insect question is one of great interest. Professor Quaintance can give us a good insight into the insects that attack pecan and other nut trees.