Codling Moth And Apple Aphis
( Originally Published Early 1900's )
PROF. R. H. PETTIT, M; A. C.
Friends—In our ordinary spraying for the codling moth we use two sprays, one spray just as the petals fall, and another spray the first week in August. Beside these, we sometimes put on another about fourteen days after the petal spray, and sometimes one between that and the first week in August. These two last sprays are applied for the scab fungus primarily but we usually add a little poison on general principles. We time the first spray something after this fashion : The petals fall, and for a while the stamen bars fill the calyx completely full. Sometimes this condition lasts for two days and if the weather is very moist sometimes for ten days but sooner or later the stamen bars will wither leaving the calyx open for two or three days, and just at that time we get the best results with an arsenical spray. I have waited in experimental work for ten days in order that the stamen bars might wither and allow the poison to fall into the calyx cup. Now, with most varieties the young sets are in perfect condition for only about two days. If we could all put on our sprays at that period we should get the optimum results but the time is too short. We have not enough rigs to get over the orchard or enough skilled men to operate the rigs so we must try to get the poison into thé calyx cup in some other way. Professor Melander of Oregon has been experimenting for some time along these lines and while his recommendations for Oregon probably will not suit our conditions in toto, still theoretically there is much to be said in favor of this plan. This idea is to force the spray in between the stamen bars so that it will fall into the calyx cup and thus utilize all the time that elapses between the falling of the petals and the closing of the calyx followed by a downward turning of the fruit. This gives us about ten days instead of two in which the work can be done. Professor Melander also advocates getting along with one spraying. I do not think we should find this to any advantage even if we could get along with one spraying, since we have to spray for scab anyway in this country and the cost of the additional poison is so little in comparison with the benefit obtained that we would all of us rather put the poison in for insurance if for nothing else. The spray to which we have referred should go on when the petals fall and should be put on under comparatively high pressure. About 200 pounds is all right. A coarse nozzle of the bordeaux type will carry the poison in between the calyx bars much better than can be done with a fine nozzle especially if the spray is directed downward from above. Of course the work must be done thoroughly. One can always check up on his work by going back over the sprayed part of the orchard and cutting open some of the little fruit sets. If one finds a drop of poison in each little set, then he knows that the work has been thoroughly done.
The second spraying in the ,first week of August is aimed at the second generation of larvae. As most of the eggs are laid on the leaves and as the young feed where they hatch out before going into the apple, a mist spray which deposits a thin layer evenly all over the foliage is best.
Now, about plant lice. For two years we have found numbers of plant louse eggs on apple trees in early spring and late in the winter. Some of you will remember finding large numbers of these eggs a year ago last winter and again last winter,—little black shiny eggs on the branches. Two years ago they were more plentiful than last year but when the season came on two years ago it was warm and dry and the plant lice hatched out all right but disappeared about blossoming time. Last summer the season was wet and cold and they started just the same as the year before only they did not stop at blossoming time, rather getting worse as the season advanced. Now, we can see the effect on the apples. Many apples in the middle part of the tree are hard and undersized.
Now, for the explanation. There are three kinds of plant lice that work on apple trees. First the common green apple louse, the rosy Iouse, and a third one. I do not know that the third one has any common name. The common green louse lives on apple trees early in the spring. About the time the blossoms open it goes to orchard grass and stays there all summer to come back about the time that apples are gathered. The other green louse leaves about the same time and goes somewhere that we lose track of it, its offspring returning also in the fall. The rosy louse stays on the apple all the year around.
When the rosy louse multiplies and keeps its numbers up all summer, then is the time we have trouble. This happens in seasons when we have a backward spring, a cold wet spring extending into the summer and the reason is because cold weather does not agree with the parasite which keeps the rosy louse in subjection. This parasite is a little wasp-like creature which thrusts its eggs through the skin into the bodies of the plant lice. There the young grubs from these eggs feed; each one on the tissues of a living host, to come out later as an adult and repeat the egg-laying process. Now, it happens that the parasites are more sensitive to temperature than are the plant lice themselves. The parasite will stop growing during cold spring days at a time when plant lice will thrive and multiply. For this reason cold, wet springs hold back the parasites for a long time giving the lice a chance to get such a start that the parasites do not catch up with them all summer.
Question—Will lime sulphur kill the eggs?
Answer—No, I think not but the old home-made lime-sulphur seemed to prevent the settling down of the young lice after they had hatched.
Question—It has been stated that salt and water would do this.
Answer—No, it will not kill the eggs. Even lime and sulphur will not kill many of them. There is nothing known at present which will kill the plant lice eggs without injuring the buds and if we get a cold, wet spring the parasites are held back so that the plant lice multiply and get such a start that they last all summer.
A Member—What is a remedy?
Answer—Dry, warm weather for spraying purposes lime and sulphur are of no use after the leaves come out. Whale oil soap costs too much. Probably the most efficient spray is nicotine. It costs a great deal but I do not know of anything that will take its place. It is at least safe.
Answer—One to seven hundred parts.
Question—What time should we use it?
Answer—That depends on the weather. Two years ago we received a great many requests for information about this same thing. The eggs were thick and were hatching out and we took a chance on spoiling our reputation and guessed that the lice would not be very bad. We guessed that way because the spring had been warm and dry and we hoped that the parasites would take care of the lice if they were let alone. We advised the people not to spray unless they felt worried about it and it turned out all right. This past season started in with lots of eggs hatching into lice but the weather had been cold and wet and we advised the use of some contact spray, nicotine, kerosene emulsion, tobacco tea or something of the sort.
Question—Can you mix this nicotine with lime-sulphur?
Answer—You do not want to mix lime-sulphur with anything until you are ready to put it on. It is claimed by the makers that you can mix nicotine sulphate with lime-sulphur safely if you do it just be-fore you apply the spray.
Mr. Hutchins The government is conducting an experiment in our section during the past summer and fall on one of the places there, and carrying it out with that same idea. They put on the arsenate of lead, and lime-sulphur at ordinary strength, and carried it with a high pressure and forced the spray right down onto the trees, which were low, and they did not give them another application for the codling moth. One spray after blossoming was given and they omitted the summer spray for the codling moth, and comparing that with the others, I have forgotten just the proportion—there was not a decided advantage with the summer spray.
The Chairman—The next topic on the program for discussion is one that we should all feel deeply interested in—one that should appeal to every fruit grower in the State of Michigan, and every fruit grower in the United States, and that is the new Sulzer Apple Law, and we will hear from Mr. R. G. Phillips, Secretary of the International Apple Shippers' Association.