THE DISEASES OF COFFEE.
Though coffee in Mysore is liable to two diseases, and to the attack of one insect, these, when the cultivation is good, and the shade suitable in kind and degree, are not likely to cause any uneasiness in the minds of the planters. But it is, of course, necessary to go carefully into the whole subject of these diseases and the insect attack, in order to bring out fully the steps that should be taken so to cultivate and shade the coffee as to render these evils as innocuous as possible, and I have therefore, in addition to my own knowledge, taken pains specially to procure from two planters of long practical experience their views. The views, I may say, of Mr. Graham Anderson as regards leaf disease are particularly valuable, as he has paid much attention to the subject.
Leaf disease is the common name given to the attack of Hemeleïa Vastatrix, a fungoid plant which distributes its spores in the form of a yellow powder. These alight on the leaves of coffee, and in weather favourable to the fungus, will germinate in about a day, and the fungoid plant then roots itself between the walls of the leaves. After the plant has completed its growth, which it generally does in about three weeks, more spores are produced to fly away with the wind, or be scattered by the movements of the coolies amongst the coffee, and thus the disease spreads. A great deal, of course, has been written about it, and those who desire more particular information may refer to Mr. Marshall Ward's report on coffee loaf disease in Ceylon. It is sufficient to say here that when the attack is severe the tree is deprived of its leaves, or of a large number of them; that much injury to the crop results; and that both the tree and the soil are heavily taxed in replacing the foliage that has been destroyed.
Leaf disease has probably existed[[56]] in Mysore as long as coffee has, but was, from the small amount of it, so entirely unnoticed, that, when I wrote my chapter on coffee in the "Experiences of a Planter," more than twenty-two years ago, I had never heard of it, nor, I am sure, had any of my neighbours. A trick, however, I once played on Mr. Graham Anderson's cousin about thirty years ago, enables me to trace it backwards so far with certainty. On coming through his plantation on one occasion, I picked oft a very large yellow coffee leaf, and placed it below the first of several plates with the aid of which he was helping his visitors. When the servant lifted the first plate, there was the leaf, and I said to my friend, "There are your golden prospects." Many years afterwards Mr. Graham Anderson recalled the incident to my memory, and said, "That was the leaf disease." But it was not till leaf disease appeared in Ceylon in a severe form that our attention was called to the subject, and since then leaf disease has undoubtedly increased, and, in the opinion of one of the two experienced planters I have consulted, has caused much loss directly and indirectly, while the other informs me it has caused much loss on some estates. But I confess my own observation causes great doubts in my own mind as to whether the losses of leaves which planters attribute to leaf disease are entirely owing to that cause, and I was much struck with what Mr. Reilly, of Hillgrove Estate, Coonoor, said to me on the subject; and when we were discussing leaf disease in general, he observed that it was often said to be the cause of leaves falling off, when their doing so was really owing to an over heavy crop of coffee. Then with our dry east winds many leaves become yellow and fall off, and some become so because they have been injured by the pickers, others from rot, and others from old age, and all these leaf losses are commonly put down to leaf disease, so that, taking all these points into consideration, I find myself quite unable to determine, even approximately, the amount of loss arising from Hemeleïa Vastatrix.
But of one thing, however, I do feel absolutely certain, and that is, that when the land is well cultivated, manured, and judiciously shaded with good caste trees, leaf disease may be reduced to such a degree that we need not trouble ourselves about it, and I feel equally sure that the most important of all the agents for controlling and limiting the disease is the shade of good caste trees. And as to the effect of shade upon Hemeleïa Vastatrix, I made particular inquiries when visiting estates in 1891 on the slopes of the Nilgiris, and conversing with planters on the subject. One manager went so far as to say that there was no leaf disease under the shade trees. Mr. Reilly, of Hillgrove Estate, said there was much less leaf disease under the shade trees. Another planter of great experience told me that leaf disease begins on the coffee in the open, and then spreads into even the finest trees under shade, but that those are affected in less degree. "In the end," he said, "You see the estate all yellow, but with green patches of coffee under the shade trees." In short, I found that all the planters I consulted were agreed in saying that there was but a small amount of leaf disease under the shade trees. The estates on the Nilgiri slopes have been originally all in the open, but latterly shade has been encouraged on some estates, but not to a degree which in Mysore would be called shade. However, the shade was quite sufficient, as we have seen, to illustrate the important fact that shade can control leaf disease. And as shade can control leaf disease, I need hardly say that it is of the utmost importance (just as it is as regards Borer), to carefully fill up at once all spots where shade is deficient, because this deficiency encourages leaf disease, and forms a breeding ground for spores to fly into the surrounding coffee. Open spots here and there may not strike one at first sight as being of much importance, but if they are all added together, the planter will see that they will amount to a considerable area of land, and quite sufficient, at any rate, to inoculate his plantation with leaf disease.
The reader will observe that I have said that leaf disease may be reduced within practically speaking harmless limits if the coffee is judiciously shaded with good caste shade trees, and I would call particular attention to the term good caste trees, because bad caste shade trees will not control leaf disease. On the contrary, Mr. Graham Anderson informs me that he has seen worse leaf disease under a dense covering of bad shade trees than he has in the open, and he also informs me that, though shade is the backbone of our success in Mysore, he has had more misfortune from all causes when his estate was under the heavy shade of bad caste trees than he has ever had since, though many places are not yet properly covered with the good kind of shade trees which he had planted to take the place of the bad ones he had removed. I am much indebted to Mr. Graham Anderson for information on the subject of leaf disease, and he has been kind enough to enumerate the following conditions under which leaf disease is liable to occur in the cases of good soils under good shade:
"In the case of good soils under good shade trees," writes Mr. Graham Anderson, "leaf disease is liable to occur under the following circumstances, or at the following times:
"1. From the soil being saturated at some critical period of growth, particularly just when secondary growth commences in September.
"2. During the time when the plants are maturing a heavy crop.
"3. After the plants have been exhausted by ripening a heavy crop.
"4. After heavy weeds—particularly if late in the season.
"5. After a heavy digging where roots have been cut.
"6. After pruning without manure having been applied, or from want of digging.[[57]]
"7. Even after manuring when the trees have large succulent roots in an immature condition—generally a sign that fibrous surface roots are deficient, and that large, deep-feeding roots are present in excess.
"8. After large quantities of green or rotting weeds have been deeply buried, or large quantities of acid, unrotted, or forcing manures have been applied.
"Leaf disease is also liable to occur:
"1. In poor gravelly soils, and on land which has caked in the hot weather, or become unmanageable during rain.
"2. On land where ill-balanced manurial preparations have been used.
"3. In soils suffering from a deficiency of the available supply of phosphates and alkalies.
"4. Under unsuitable shade trees."
Now it is to be observed that these are preventable causes, or aggravations of leaf disease, and, if carefully attended to, the planter will have little to apprehend from leaf disease. Mr. Anderson, in his communication to me, lays, and very rightly, particular stress on the maintenance of the physical condition of the land and its state of fertility. And it is satisfactory to find that he is exactly confirmed by Mr. H. Marshall Ward in his third report (dated 1881) on coffee leaf disease in Ceylon, and he points out (p. 3) that "Leaf disease appears to affect different estates in different degrees on account of varieties in soil, climate, and other physical peculiarities."
"But," he continues, "I would draw particular attention to this. Careful cultivation and natural advantages of soil, climate, etc., enable certain estates to stand forth prominently, as though leaf disease did not affect them, or only to a slight extent, while poor nutrition, the ravages of insects, etc., have in other cases their effects as well as leaf disease." Or, in other words, he states that, as was suggested to me by Mr. Reilly—a planter of long experience near Coonoor on the Nilgiris—that much loss of leaves, which has been attributed to leaf disease, is often due to other causes.
Mr. Brooke Mockett—one of the planters previously alluded to—informs me that "Leaf disease is certainly worst (1) on trees that are cropping heavily, (2) on trees that have been severely pruned (heavy pruning being ruination in my opinion), (3) on plants under bad caste shade trees (these plants it seems to cripple), and (4) on plants in the open."
It is worthy of note that the Coorg plant is not nearly so liable to attacks of leaf disease as the original Mysore Chick plant. I have seen a tall plant of the latter variety heavily attacked, while a Coorg plant partly under it was only slightly attacked on the side next the Chick plant, and hardly at all on the side not under the Chick plant. I observe, too, from the Planting Correspondent's Notes in the "Madras Mail" of January 30th, 1892, that the same thing has been observed in Coorg, and that occasional Mysore plants, which had by some accident found their way into the Coorg coffee, got the disease first, and that it then spread into the surrounding coffee.
It should be borne in mind that leaf disease does not kill the tree, but only injures it, and diminishes its powers by depriving it of much of its foliage, so that there is nothing alarming in leaf disease when it is controlled by good management of the tree, and good shade, cultivation of the soil, and manuring; and the only case I can hear of where anything like permanent injury has occurred, is where the disease has existed under the shade of bad caste trees. But it is far otherwise with the justly dreaded Borer insect, which, however, can, as we shall see, be effectively controlled by good shade. To the attacks of this insect I now propose to direct the attention of the reader.
The too well-known coffee Borer is a beetle, about as large as a horsefly, which lays its eggs in any convenient crevice, and generally, it is supposed, near the head of the tree, in the bark, or wood of the coffee tree. After the larvæ are hatched they at once burrow their way into the tree, where they live on the dead matter of the inner or heart-wood of the stem, and there they reside from, it is supposed, three to five months, till their transformation into winged beetles. Then they bore their way out of the tree, and fly away to carry on their mischievous work. This insect has been declared to be, by Mr. John Keast Lord, "a beetle of the second family of the Coleoptera Cerambycidæ, and to be closely allied to a somewhat common species known as the wasp-beetle (Clytus avietis), which usually undergoes its changes in old dry palings." And in a collection made by M. Chevrolat in Southern India, and now in the British Museum (at least it was so in 1867, when Mr. Lord investigated the point), a specimen was found, to which the name of Xylotrechus quadrupes was attached. This Borer, like the leaf disease, has probably always attacked coffee, but the earliest probable notice of it is to be found in Mr. Stokes's Report on the Nuggur Division of Mysore, in about 1835, where he observes that coffee trees in dry seasons often wither and snap off suddenly at the root. The cause, or probable cause of this he does not state, but there can be little doubt that the Borer had attacked the trees alluded to. Since then the Borer seems to have attracted little or no attention till towards the end of 1866, but about that time, and during the three following years, an alarming attack of Borer took place, and inflicted immense injury on plantations, and there can be no doubt that this was in a great measure owing partly to insufficient shade, and partly to bad caste shade trees, accompanied by dry, hot seasons, which were favourable to the hatching of the eggs of this destructive insect. But since then much attention has been paid to shade, both as to quantity and kind, and the Borer may now be regarded as an insect which can with certainty be held in check if the land is properly shaded with good caste trees. And I say good caste trees, because bad caste trees encourage Borers, and Mr. Graham Anderson, who has had a very large and disagreeable experience of the effects of bad caste trees, informs me that he has "seen worse Borer under dense bad caste shade than in open places in good soil on northern slopes." "Some bad shade trees," he continues, in his communication to me on the subject, "keep the coffee in a debilitated state. They allow it to be parched up in the dry weather, and they smother it in the monsoon. They rob it of moisture and manure with their myriads of surface-feeding roots, and prevent dew and light showers benefiting the plant. I do not fear Borer under well-regulated shade of approved descriptions. Renovation pits left open in the hot weather, large clod-digging in a light soil even under fair shade, weeds left standing in dry weather; all these, by increasing evaporation, tend to cause increase of damage from Borer. A hard caked surface, or a compact, undug soil is equally bad. Rubbing and cleaning the stems is a valuable operation, because it removes rough bark in which eggs may be deposited, and contributes to the health of the tree. The prompt removal and burning of all affected trees, properly arranged shade of selected varieties, frequent light stirring of the surface soil, having well arranged shoots distributed all over the coffee trees, not opening the centre of the trees too much, and keeping the trees succulent and vigorous by culture and manure, may be at present classed among the best remedies for the Borer pest." In other words, he would say that the Borer loves dry wood. Keep your coffee tree green and succulent and well shaded, and you have little to fear from it.
I have also obtained the opinion of Mr. Brooke Mockett, who informs me that "Borer is certainly as destructive under bad caste trees as in the open." "Borer," he continues, in his communication to me on the subject, "is always much worse in land where there has been a burn than in unburnt land. It is also bad in rocky and stony places. In good soil, where there has been no burn, I have never had Borer severely, even though for a time there has been no shade whatever. I do not fear Borer now that such an excellent system of shade raising has been discovered. Rubbing stems once in about three years I look upon as of great use."
I too have had great experience of Borer, and agree with what my friends have written on the subject, with the exception of what Mr. Graham Anderson has said as to the advisability of promptly removing and burning all bored trees. This I am aware is the common practice, but I have never carried it out on my property, and yet, though the trees were riddled with Borer in the great Borer years, and I have had since then a fair proportion of it on some part of my property, I believe that no estate has less Borer now. Instead of removing the bored trees I removed the Borer itself with the aid of the shade of good caste trees, and especially, I believe, by paying strict attention to what I have particularly enforced in my shade section—the prompt filling up of every spot in the plantation that called for more shade. For it is in such spots that the Borer first locates itself, and then it spreads to other dried up trees in the plantation. There is little use, I think, in removing the affected trees. You must remove the cause of their being affected, because, if you do not, the sound trees that are insufficiently shaded will in time be affected: and then it must be remembered that the Borer is a winged insect which, as long as you leave suitable ground for it, will be sure to make its appearance. Out of curiosity I lately cut down and carefully examined a coffee tree which I could see, from the appearance of the bark, had once been heavily bored, but which I felt certain had no Borer now, nor any recent attack of it. The tree I found, after a careful dissection, had not a sign of Borer present in it, nor any sign of a recent attack, and yet in years gone by it had been heavily attacked and bored literally from end to end of the stem. The explanation was that the land had formerly not been sufficiently shaded, while now the shade is ample. The Borers had then left the trees, and their descendants had either not thought it worth while to lay any eggs on them, or the eggs had, from the lowered temperature caused by the shade, become addled. Many years ago I remember cutting down a fine coffee tree, when the round gimlet-made looking hole through which the insect makes its escape was plainly to be seen, when I found that a single Borer had drilled a hole down a part of the centre of the tree, then passed into the fly state and left the tree. It was a fine succulent and nourishing tree, and would, in all probability, have not again been attacked. To remove, then, all attacked trees, as some planters do, seems to me to be a great waste. To do so will not prevent other Borers arriving from some quarter or other to continue the deadly work; but shade, if it does not prevent their arrival, either prevents the insect from laying its eggs, from instinctively feeling that the ground is unsuitable for their being hatched, or causes the eggs to become addled. But whatever the cause may be, it is certain that succulent trees in well shaded land will not suffer from Borer, while it is equally certain that coffee trees in a dried up state, and with either insufficient shade, or shade of bad caste trees over them, are certain to be attacked by Borer again and again, and will eventually be killed.
I turn, lastly, to the consideration of a disease in coffee which is popularly known by the name of rot, and scientifically as pellicularia koleroga, a fungoid plant which crawls over the leaves and seals up their breathing pores, till at last the leaf dies, as man does, from want of breath. On one of my estates we have had a considerable experience of it, and, whatever may cause rot, I feel sure that what aggravates it, and causes it to be very injurious, is the want of free circulation of air over the land, and through the coffee trees; and I am the more convinced of this because we have found rot worse in the open, and where there was little undecayed vegetable matter present in the soil, than in rather thick shade with abundance of undecayed vegetable matter on the surface. But in the latter case the land is on a rather high ridge exposed to the constant winds of the south-west monsoon, while in the former case the land was in a hollow under a hill which lies between it and the west—a hollow completely sheltered from the wind. And it is in such sheltered spots that we find rot worse, and quite independently of the presence or absence of shade or of vegetable matter lying on the land. To check rot, then, the free circulation of air is necessary both over the land and through the plant. Much may be done in the first case by judiciously opening channels for air through the shade trees so as to admit a free circulation of air into hollows, and much in the latter by freely handling out the centres of the trees which, in the monsoon, and especially in hollows, are apt to grow a superabundance of young wood, which chokes up the centre of the tree and thus hinders the free circulation of air. The soil, too, is often excessively saturated in these hollows, and, where this is the case, the land should be surface drained. Though I have not as yet adopted the plan of sweeping up and putting into the manure heap, or burying with a little lime added, the numerous dead leaves that are apt to drift into hollows, I feel sure that either of these plans would be attended with advantage, by lessening damp, and allowing a free circulation of air over the land. I am confident, I may add here, that the removal of the lower branches of the coffee trees, branches which in any case bear hardly anything in well-shaded land, would be of great advantage in lessening the damp in the plantation, and so diminishing the causes that promote rot.
With reference to rot, it is of great importance to thin out young wood as early as possible, so that, when the rot season arrives, the trees may have a moderate amount of well-matured young wood, with fully-developed hardened leaves, instead of a largo number of small succulent shoots covered with succulent leaves, which are very apt to be rotted bodily away. And the importance of this is equally great with reference to leaf disease, and Mr. Ward, in his "Report" (p. 15), points out that pruning and manuring should be so timed that the tree may have, at the beginning of the wet weather, mature wood and leaves, and the whole of his observations on this head point to the conclusion that manuring ought to be carried out at the close of the monsoon, and that pruning, which encourages the growth of much young wood, should be limited as much as possible to the removal of utterly useless, worn-out wood. Under the head of pruning and handling, the reader will find some remarks with reference to the important subject of the best time for pruning so as to limit rot and leaf disease.
I am glad to say that I have no other pests to chronicle as regard Mysore estates, but as estates on the Nilgiris sometimes suffer from green-bugs, I give the following treatment, which was discovered, and has been effectually used by Mr. Reilly of Hill Grove Estate, Coonoor, who has kindly permitted me to publish the recipe.
For every 30 or 35 gallons of water take a bundle of wild merang (Leucas zeylanica or (Kanarese) Thumba Soppu) plants about two feet in diameter, and, after removing the roots, boil it for about four or five hours, and let it cool all night, and in the morning apply the decoction to the coffee trees affected, with the aid of a garden syringe. The trees should be well syringed, and it is advisable to give the tree a second application. The refuse of the boiled plant should be scattered on the ground around the stem of the tree.
This prescription might probably be useful in the case of garden plants or shrubs which have been attacked by insects.
[56] Mr. Reilly, of Hillgrove Estate, Coonoor, told me that he had first noticed leaf disease about twenty-six years ago. It commenced low down on the coffee on the Coonoor Ghaut, and then came gradually up the Ghaut.
[57] A planter on the slopes of the Nilgiris gave me a well marked instance of leaf disease being increased from want of digging, when there was a good opportunity of contrasting the dug with the undug soil.