Spraying Plums for Brown Rot.
PROF. E. C. STAKMAN, MINN. EXP. STATION, UNIVERSITY FARM, ST. PAUL.
The brown rot of plum is without doubt one of the important limiting factors in plum-growing in Minnesota. In seasons favorable to its development, losses of from twenty to fifty per cent. of the crop in individual orchards are not uncommon.
Experiments on the control of the disease have been carried on by the sections of "Plant Pathology and Tree Insects and Spraying," of the Minnesota Experiment Station, since 1911. No accurate results could be obtained in 1912 and 1915 on account of crop failure in the orchards selected for experiment. Results are available for the years 1911, 1913 and 1914.
Brown rot is caused by a fungus (Sclerotinia cinerea (Bon.) Wor.). Every plum grower knows the signs of the disease on the fruit. Blossoms, leaves and twigs may also be affected. The diseased blossoms become brown and dry, and fall from the tree; the diseased leaves become brown and may die. Young twigs may also be killed.
Infection may occur at blossoming-time. The amount of blossom blight depends very largely on weather conditions; in fairly warm, moist weather there is usually more than in drier weather. The same is true of the rot on the fruit; during periods of muggy weather it may spread with amazing rapidity. The rot does not usually attack the fruit until it is nearly or quite ripe, although green plums may rot, especially if they have been injured. It is important to know that a large percentage of rotted plums have been injured by curculio. Counts have shown that in many cases as much as eighty-five per cent. of the rot followed such injury.
Rotted plums should be destroyed for two reasons: (1) The spores produced on them may live during the winter and cause infection in the spring; (2) if the mummies fall to the ground, late in April or early in May of the second spring the cup fungus stage may develop on them. This cup fungus produces a crop of spores capable of causing infection.
Spraying experiments, the summarized results of which are given here, show that the disease can be fairly well controlled even in badly affected orchards.
Some of the experiments were carried on in the orchards at University Farm and some in commercial orchards. There were from twelve to forty-five trees in each plot, and the trees on which counts were to be made were selected before the rot appeared. The percentages given below refer to fruit rot and do not include blossom or twig blight. The object was to determine the times for spraying and the most effective spray mixtures. Details are for the most part omitted, and the results of various experiments are averaged.
For convenience the times of spraying are designated as follows:
1. When buds are still dormant.
2. When blossom buds begin to show pink.
3. When fruit is size of a pea.
4. Two weeks after third spraying.
5. When fruit begins to color.
It did not pay to apply Spray 1. In the plots on which applications 1, 2, 3 and 4 were made there was an average of 6.3 per cent. of rot, while in those from which Spray 1 was omitted there was an average of 6.7 per cent. rot, a difference so slight as to be negligible. Neither did Spray 4 seem to pay, there being an average of 10.9 per cent. brown rot when it was applied and 11.4 per cent. when it was omitted.
The schedule finally adopted was therefore the application of Sprays 2, 3, and 5. Spray 2 is necessary to prevent blossom blight, although it has not always reduced the amount of rot on the fruit. Spray 5 is the most important in reducing the amount of rot. In all of the experiments during three years the average amount of rot in the sprayed plots which did not receive Spray 5, was 10.7 per cent. On the plots which received Spray 5, with or without the other sprays, the average amount of rot was 4.6 per cent., and the average on unsprayed plots was 34.8 per cent. Excellent results were sometimes obtained by applying only Spray 5, although this did not, of course, have any effect on blossom blight. In 1913 the amount of brown rot in one plot which received only Spray 5 was 3.3 per cent., while in the unsprayed plots it was 33.9 per cent. In 1914 the amount of rot was reduced from 38.8 per cent. in unsprayed plots to 6.5 per cent. in the plots to which Spray 5 was applied. Possibly Spray 3 could be omitted without seriously interfering with results; success in controlling the rot with Spray 5 alone seems to indicate this. It was hoped to settle the matter during the past summer, but spring frosts spoiled the experiment.
For the present it seems advisable to recommend the application of Sprays 2, 3, and 5. In the first two, two and a half pounds of arsenate of lead paste, or one and one-fourth pounds of the powder should be added to each fifty gallons of spray mixture in order to kill the curculio. In the plots sprayed in this way in 1911 ninety-six per cent. of the fruit was perfect, while in the unsprayed plots only 81.6 per cent. was perfect, and in 1913 and 1914 the amount of brown rot was reduced from 34.8 per cent. to 4.6 per cent. Several growers have reported excellent results from these three applications, and there is no reason why other growers should not duplicate them.
Brown rot of plums showing the small, grayish brown tufts of spores. Can be controlled by destroying mummies and thorough spraying.
The efficiency of various fungicides was tried. Self-boiled lime-sulphur, 8-8-50; commercial lime-sulphur, 1 to 40; 2-4-50 and 3-4-50 Bordeaux; iron sulphide made up with 1 to 40 commercial lime-sulphur, and iron sulphide made up with 10-10-50 self-boiled lime-sulphur were tried and all gave good results. Commercial lime-sulphur, 1 to 40, has been used in commercial orchards with excellent results, and it will probably be used more than the other spray mixtures because it is so easy to use. Possibly weaker solutions of lime-sulphur would do just as well as 1 to 40. This will be determined, if possible, during the summer of 1916.
Good results were obtained only when a high pressure was maintained in spraying. There was a clearly observable difference between plots sprayed with low pressure and those sprayed with a pressure of more than 175 pounds. For large orchards a power sprayer is desirable; for small orchards a barrel sprayer with an air-pressure tank attached is large enough. Such an outfit can be bought for $35 or $40 and can do good work.
The cost of spraying three times should not exceed fifteen cents a tree. The results from spraying orchards which contain a great deal of brown rot and have never before been sprayed will probably not be so good the first year as in better kept orchards, but by spraying regularly each season the disease can be well controlled.
Mr. Cashman: Please state what you mean by 3-4-50 there.
Mr. Stakman: 3-4-50 Bordeaux mixture means three pounds of bluestone or copper sulphate, four pounds of lime, and fifty gallons of water. The copper sulphate should be dissolved in twenty-five gallons of water, the best way being to put it into a sack and hang the sack in the water. The lime should be slaked and then enough water added to make twenty-five gallons of milk of lime. Here is where the important part of making up the spray comes in. Two people should work together and pour the milk of lime and the bluestone solution together so that the streams mix in pouring. It is very important that the mixing be thorough and the mixture should be used fresh.
The President: Do you add any Paris green at any time or arsenate of lead?
Mr. Stakman: Always add arsenate of lead two times, when the buds are swelling and when the plums are the size of green peas.
The President: How much?
Mr. Stakman: I would rather leave that to Professor Ruggles. We used from 2-1/2 to 3 pounds and Mr. Ruggles, I think, found 2-1/2 pounds was enough.
The President: That is, 2-1/2 pounds to 50 gallons of water with the other ingredients?
Mr. Stakman: Yes.
Mr. Dyer: I would like to ask if you have ever used arsenate of lead for spraying plums?
Mr. Stakman: In the experiments which we conducted in co-operation with Mr. Ruggles, of the Division of Entomology, we always used arsenate of lead in the first two sprayings to kill the curculio.
Mr. Dyer: I had quite an experience, so I want to know what your experience was.
Mr. Stakman: We never had any trouble with it.
Mr. Dyer: I have had an experience of thirty years, and I have never seen or had on my place any brown rot, and I never was troubled with any curculio, and I practically always used arsenate of lead.
Mr. Cashman: Isn't it a fact if you begin spraying your plum trees when they are young and spray them early, at the right time, you have very little trouble with the brown rot? And spray them every year?
Mr. Stakman: Yes, that is it. You might be disappointed the first year if the orchard had never been sprayed, but by spraying year after year you finally cut it down.
Mr. Cashman: You said a pressure of 200 pounds ought to be used?
Mr. Stakman: Yes, but it isn't necessary to get an expensive power sprayer to keep up that pressure. There are sprayers on the market that cost from $30 to $40 which have a pressure tank by which the pressure can be maintained at from 175 to 250 pounds without any great amount of trouble, that is, for a small orchard. If you have a big enough orchard for a power sprayer, of course get it.
Mr. M'Clelland: This summer my plum trees, the leaves all turned brown and came off. What is the reason?
Mr. Stakman: When did it happen?
Mr. M'Clelland: Along in August, I think; July or August.
Mr. Stakman: What kind of soil were they on?
Mr. M'Clelland: Clay.
Mr. Stakman: Did you spray?
Mr. M'Clelland: Yes, sir, I sprayed.
Mr. Stakman: What did you use?
Mr. M'Clelland: Lime-sulphur, I think.
Mr. Stakman: Did the whole leaf turn brown?
Mr. M'Clelland: Yes, sir, the whole leaf turned brown and came off.
Mr. Stakman: How strong did you use the lime-sulphur?
Mr. M'Clelland: Not very strong.
Mr. Stakman: If you use very strong lime-sulphur you sometimes get such an effect on both plums and apples. Sometimes the leaves fall, and almost immediately you get a new crop of leaves.
Mr. M'Clelland: This was in August.
Mr. Stakman: There was a perfect crop of new leaves?
Mr. M'Clelland: Yes, sir.
Mr. Stakman: My only suggestion would be that you used the lime-sulphur too strong. That might account for it.
Mr. Sauter: I never sprayed until this year. I tried it this year and with good results. I sprayed my apple trees at the same time, and I sprayed the plums with the same thing I sprayed the apple trees with. I had nice plums and nice apples; last year I had hardly any.
Mr. Stakman: What did you use?
Mr. Sauter: Lime-sulphur and some black leaf mixture. I used it on the plum trees and the apple trees, and afterwards I used arsenate of lead.
Mr. Stakman: You didn't get any injury to the plum trees?
Mr. Sauter: No, sir, we had nice plums.
A Member: I have seventeen plum trees, and I have only sprayed with kerosene emulsion and the second time put in some Paris green, and I have never seen any of the brown rot, but there have been a good many of the black aphids on the plum trees, on the end of the branches. I cut them off and burned them. I didn't know whether that would be the end of it or not.
Mr. Ruggles: Why don't you use "black leaf 40," 1/2 pint in 50 gallons of the spray liquid. It can be used in combination with arsenate of lead and lime-sulphur or arsenate of lead and Bordeaux mixture.
If you wash them with black leaf 40 it will kill all the aphids. I did that myself this summer.
A Member: Please give us a little better explanation of what black leaf 40 is.
Mr. Ruggles: It is an extract of tobacco that is for sale by wholesale drug companies and stores, or you can get it from Kentucky, from the Tobacco Products Company, at Louisville, Ky., or Grasseli Chemical Co., St. Paul. I am not advertising, Mr. President, but they will send you a small package for seventy-five cents, about half a pint. Of course, that looks kind of expensive, but it will go a long way. I think possibly it is the best thing we have to combat lice.
Mr. Stakman: Plum pocket is caused by a fungus which is supposed to infect mostly when the flower buds are just beginning to swell, especially in cold, wet weather. Plum pocket causes the fruit to overgrow and destroys the pit, and big bladder or sack-like fruits are produced instead of the normal fruit. The fungus that causes it gets into the twig and is supposed to live there year after year. Therefore pathologists usually recommend cutting out and burning affected branches and even trees that bear pocketed plums several seasons in succession. Our experiments with plum pocket have not extended far enough to enable me to say anything definite about it.
Mr. Hall: With us in western Minnesota this year this plum pocket got all the plums that the frost didn't get. If we were to cut off the twigs we would have to chop off the trees.
Mr. Stakman: When a tree becomes so badly infected that practically all of the branches produce pocketed plums year after year you can't expect very much normal fruit. Sometimes you might get some, but usually not very many.
Mr. Graves (Wisconsin): Do you use your black leaf 40 in conjunction with your Bordeaux or lime-sulphur?
Mr. Ruggles: Yes, you can.
Mr. Graves: Doesn't it counteract the result?
Mr. Ruggles: No, it does not.
Mr. Stakman: I used this year lime-sulphur and black leaf 40 together.
Mr. Graves: You say you got the same results from black leaf 40 in that mixture?
Mr. Stakman: It killed the plant lice; that is all I wanted.
Mr. Graves: We had some experiences that indicated that black leaf counteracted the other results.
Mr. Stakman: Yes, sir, I think that has been the impression, but I think there have been some experiments more recently to show that the black leaf 40 can be used in conjunction with other sprays without counteracting their results.
Mr. Richardson: Did you ever know the plum pocket to come unless we had cold weather about the time of blossoming and lots of east wind?
Mr. Stakman: Yes, a little; I have seen it mostly when there was cold weather, however, and as I said before it usually isn't so serious unless there is cold, wet weather.
Mr. Richardson: I settled out in Martin County, Minnesota, in 1866, and in all my experience I never saw plum pocket unless we had the right kind of cold weather at the time of the blossoming. I had my plums all killed and destroyed one year and never did anything for it, and when we had the right kind of weather I never had any trouble.
Mr. Stakman: When you have cold, wet weather, as I mentioned before, infection takes place much more rapidly than it does at other times. There is some evidence to show that the fungus lives in the twigs and that affected ones should be cut out.
Mr. Richardson: Yes, but these didn't bear any for four or five years, and when we got the right kind of weather I got good plums.
Mr. Norwood: My experience is something like this man's. I have had my plums killed off as many as five years with the plum pocket and then had a good crop of plums. I sprayed with lime-sulphur.
Mr. Stakman: When did you spray?
Mr. Norwood: I spray just before the buds open.
Mr. Stakman: The flower or leaf?
Mr. Norwood: Flower, and then I spray when the plums are well started, just before they begin to ripen.
Mr. Stakman: Were you spraying for the pocket or brown rot?
Mr. Norwood: I used lime-sulphur and arsenate of lime.
Mr. Stakman: Of course, spraying after buds open wouldn't do any good for the plum pockets at all.
Mr. Norwood: I spray mainly for the brown rot, and I have pretty good luck.
Mr. Cashman: Have you had any experience in using orchard heaters to save plums in cold nights?
Mr. Stakman: I will ask Mr. Cady to answer that.
Mr. Cady: No, I haven't tried to use them.
Mr. Cashman: We tried it this year, and we saved our plum crop. We have tried it the last four years and saved our plum crop each year. We also sprayed each year and had a very good crop of plums when neighbors who had not sprayed had very few, and I am satisfied if we use the proper ingredients and spray properly at the right time, and occasionally use an orchard heater when there is any danger of freezing, that we will raise a good crop of most any plum that is hardy enough for this climate.
A Member: What kind of heaters do you use?
Mr. Cashman: We use oil heaters. We use crude oil, the same oil we use in our tractor engine.
A Member: Where do you buy your heaters?
Mr. Cashman: We have them made at the hardware store, of sheet iron, with a cover. We put about two gallons of oil in this heater. There is a small piece of waste that is used as a wick, which we light from a torch. It will heat quite a large space sufficiently for two or three hours and prevent frost.
Mrs. Glenzke: Do you put a canvas over the tree or leave it uncovered?
Mr. Cashman: We do not put anything over the tree.
Mr. Stakman: What does your oil cost?
Mr. Cashman: About eight or nine cents a gallon.
Prof. Hansen: Just a thought occurred to me that out west on the Pacific coast where men have to get down to business in order to raise fruit they have these horticultural commissioners that have absolute police power to make orchard men clean up. They will come into your old orchard and pull it up and burn it and add it to your taxes, charge it up to you, if you don't clean up. The same sort of police power should prevail here. If a man has an old plum orchard that is diseased through and through, it won't do for him to tell his tale of woe year after year and not do anything. A county agent will come along and clean it up for him. After it is cleaned up it will be an easier proposition. If you are not going to keep up with the times and spray, then the county agent ought to have police power to burn the orchard. Either spray or go out of the plum business.
To Make Concentrated Apple Cider on a Commercial Scale.—The specialists of the fruit and vegetable utilization laboratory of the department have completed arrangements for a commercial test of the recently discovered method of concentrating apple cider by freezing and centrifugal methods. As a result, a cider mill in the Hood River Valley, Ore., will this fall undertake to manufacture and put on the retail market 1,000 gallons of concentrated cider, which will represent 5,000 gallons of ordinary apple cider with only the water removed.
The new method, it is believed, makes possible the concentrating of cider in such a way that it will keep better than raw cider, and also be so reduced in bulk that it can be shipped profitably long distances from the apple growing regions. The old attempts to concentrate cider by boiling have been failures because heat destroys the delicate flavor of cider. Under the new method nothing is taken from the cider but the water, and the resultant product is a thick liquid which contains all the apple-juice products and which can be restored to excellent sweet cider by the simple addition of four parts of water. The shippers and consumers, therefore, avoid paying freight on the water in ordinary cider. In addition, the product, when properly barreled, because of its higher amount of sugar, keeps better than raw cider, which quickly turns to vinegar.
The process, as described by the department's specialists, consists of freezing ordinary cider solid. The cider ice is then crushed and put into centrifugal machines such as are used in making cane sugar. When the cider ice is whirled rapidly the concentrated juice is thrown off and collected. The water remains in the machine as ice.
At ordinary household refrigerator temperatures this syrup-like cider will keep perfectly for a month or six weeks, and if kept at low temperatures in cold storage will keep for prolonged periods. At ordinary house temperatures it, of course, will keep a shorter time.
To make the concentrated syrup, the cider mill must add to its equipment an ice-making machine and centrifugal machinery, so that the process is not practicable on a small scale. The specialists are hopeful, however, that the commercial test soon to be inaugurated in Oregon will show that it will be possible for apple growers to concentrate their excess cider and ship it profitably to the far South or to other non-producing regions. The specialists also believe that it will enable apple producers to prolong the market for cider.—U. S. Dept. of Agri., Oct., 1914.