of the United States it would not be necessary or desirable to spray with poison so late in the season and this being the case the poison which would remain on the fruit from ordinary spraying, would be much less than the amounts recorded in the paper presented. PRESIDENT W. D. HUNTER: The next paper will be by Mr. G. D. Shafer on, "How Contact Insecticides Kill.”

HOW CONTACT INSECTICIDES KILL

By G. D. SHAFER, Lansing, Mich.

(Withdrawn for publication elsehere.)

PRESIDENT W. D. HUNTER: As the amount of time remaining is very limited it has been suggested that Dr. Felt's paper be read and discussed and that the remaining papers be placed on the program for the next session. If there is no objection we now will listen to the paper by Dr. Felt, entitled, "Injuries Following the Application of Petroleum and Petroleum Products to Dormant Trees."

INJURIES FOLLOWING THE APPLICATION OF PETROLEUM OR PETROLEUM PRODUCTS TO DORMANT TREES

(Abstract)

By E. P. FELT, Albany, N. Y.

Attention was called in a summary manner to earlier injuries in New York state by petroleum or mechanical emulsions of the same. More recent damage following the application of miscible oils to hard maples and apple trees was briefly described. The conclusions reached were as follows:

The use of oils or oil preparations on dormant trees has been followed in several cases by severe injury.

Trees, as living organisms, respond to climatic and cultural conditions and, as a consequence, their power of resisting penetration and injury by oils undoubtedly varies with the season and probably from year to year.

Since certain weather conditions promote injury by oils, it appears impossible to be certain that deleterious effects may not follow spraying trees with an oil or oil preparation.

Fall treatment with an oil appears to be more hazardous than spring applications.

Other things being equal, we believe there is less danger of penetration by oil and a consequent injury if the applications are made

in the spring shortly before active growth begins, and presumably offers greater obstacles to entrance by oil or quickly replaces destroyed and necessary vital tissues.

PRESIDENT W. D. HUNTER: This paper is now open for discussion. [The following has been supplied by Mr. Yothers as a substitute for his remarks. Ed.]

THE EFFECTS OF OIL INSECTICIDES ON CITRUS TREES AND FRUITS

By W. W. YOTHERS, Bureau of Entomology

The effect on citrus trees and fruits of those commercial and homemade insecticides having a mineral oil base is of primary importance. This is especially the case since these are the only kinds of insecticides which have been found up to this time to be effective in controlling the white-flies, and the grower who desires to spray has no alternative. Their effectiveness against scale insects and rust mites also increases the importance of this subject.

As a general proposition their use is attended with little, if any, danger to the trees or fruit. On the other hand, the killing of the insects results in great benefit to the tree. There are certain chemicals, however, which usually cause damage when applied to the trees in the form of a spray and there are certain practices which should be followed in the use of oil sprays on citrus trees.

The use of sulphuric acid in a spray should be avoided. One brand of commercial miscible oil contained 2 per cent of sulphuric acid according to the analysis of the Bureau of Chemistry. Dozens of tests were made with this insecticide and every one resulted in some form of injury. When used at a strength of 13 per cent of oil or 1 part of insecticide to about 55 parts of water in the winter, a large part of the leaves fell and holes were burned in others that remained on the trees. So far as observed no twigs were killed. It is very doubtful, however, if this in the least made the following crop of fruit less. When used in April when the oranges were about to inch in diameter, at 1 per cent of the oil contents the new leaves were injured and many new and old leaves fell. About three fourths of the crop of fruit fell or was so badly scarred as to be unsalable. When used in April at of 1 per cent of the oil contents or about 1 part of insecticide to 170 parts of water, it burned holes in the new leaves, and the results even at this weak dilution were so disastrous as to prevent

Published by permission of the Chief of the Bureau of Entomology.

Since it requires a dilution of spraying material containing approximately 1 per cent of oil to be effective against the insects. further experiments were discontinued. According to our observations this acid did not increase the insecticidal qualities of the spray. We were unable to test sulphuric acid in any of the formulæ since. it always prevented the emulsification of the oil by the soap.

The use of rosin or rosin oil should also be avoided. One brand of commercial miscible oil contained a considerable percentage of rosin oil and this, while not so injurious as sulphuric acid, burned the leaves and fruit when used at 1 per cent of the oil contents. The use of rosin oil in the home-made products always resulted either in great damage or unfavorably. One sixth of 1 per cent used in a spray containing 2 per cent of oil caused many more leaves to fall than where the same amount of oil in a spray without the rosin oil was used. When used in May on oranges 1 inches in diameter at 1 quart rosin oil to the emulsion required to make of 1 per cent of petroleum fuel oil for 200 gallons of water or of 1 per cent of rosin oil, large areas were scarred. This injury was usually found on the lower part of the orange where the drop of spray had collected. Rosin oil did not increase the insecticidal qualities as much as it was expected and since it costs about three times as much as the paraffine oil, we strongly advise against its use.

Experiments with another miscible oil, made on the same dates and in the same groves, using exactly the same percentages of oil as was used in the experiments with the above brands, gave only good results. It did not burn the leaves nor fruit and did not cause an excessive shedding of leaves in the winter. The analysis showed this product to be free from sulphuric acid and rosin oil, and to contain only such chemicals as were necessary for the proper emulsification of the oil used in its manufacture.

Much work was done with emulsions of petroleum fuel oil 24° Baumé, distillate or gas oil 28° Baumé, and two paraffine oils of 24° and 28° Baumé, respectively. The extensive use of these oils at proper strengths did no immediate damage to the foliage or fruit.

While it is a fact that oil sprays made without injurious chemicals and used properly cause no immediate damage and never any serious injury, they apparently interfere to a limited extent with the physiological processes of the tree. On March 30 and 31, 1911, a row of about 20 trees each was sprayed with petroleum fuel oil 1 per cent, distillate oil 1 per cent, paraffine oil 28° Baumé 1 per cent, and paraffine oil 24° Baumé 1 per cent. At the time of the application the leaves were the new ones of the first spring growth and had not become very green but were of a light yellowish green color.

After about two weeks it was noticed that the leaves of those trees that had been sprayed were still of a slight yellowish green and those left unsprayed had changed into a dark green. At the end of a month this difference had entirely disappeared, and so far as could be ascertained no permanent injury had been done. Although some difference may have existed according to our observations, none could be detected between those leaves sprayed with the distillate which was somewhat volatile and the heavy paraffine oil of 24° Baumé, which was very stable. This observation would indicate that the coating of the new leaves with oil spray interfered to a limited extent with the formation of chlorophyll.

The excessive use of sprays may be injurious and some tests were made to determine the accumulated effect of one of the above oils. The same trees were sprayed with the paraffine oil 24° Baumé using 1 per cent of oil in the spray three times at intervals of six weeks during the summer, the first application being made May 13, 1911. The effect of these repeated applications was very marked. The leaves were small as compared with those from other trees. There were considerable dead twigs in the trees and the fruit was very small and very late and sour compared with the fruit from adjoining trees. There was no yellowing of the leaves, nor burning of the leaves nor fruit by these applications. The trees sprayed only once on May 13 and a check on the above were much improved by the application. It should be stated that a single application of a spray containing 1 per cent of the above oil instead of 1 per cent as was used would have been sufficient to eliminate the damage caused by insects. No experiments were conducted to determine the accumulated effect of as weak a dilution as of 1 per cent of oil but it is the opinion of the writer that such a dilution would not be injurious even though. used very frequently.

The weather conditions which may exist at the time of the application may be of much importance. It has been known since Hubbard made his investigations that low temperatures following the application of kerosene emulsion would result in injury. This is due to the low temperatures preventing the evaporation of the kerosene, thus permitting it to remain for too long a time in contact with the leaves and interfere with their function. Those oils used in the manufacture of miscible oils as well as the petroleum fuel oil, distillate oil, and the paraffine oils are much less volatile than kerosene and consequently just as liable to cause injury when the application is followed by low temperatures. The author has sprayed thousands of trees and known of other thousands sprayed by other people and only one or two instances are known to him that disastrous results

followed. It is well, however, to cease spraying just before a freeze is predicted. It is well known that neither hot sun, nor shade, neither rain nor dry weather existing either during or following the application is influential in causing damage.

As yet no experiments have been conducted to determine the effect. of these sprays on the bloom and it is inadvisable to use them during the blooming period.

It has been observed that the use of these oils, including kerosene emulsion, causes dim shadows or faint green blotches to appear on the fruit if sprayed early in the season. These disappear when the fruit colors up in the fall and this has never been considered a serious matter by the author.

MR. H. J. QUAYLE: I agree with Mr. Yothers that the injury may be due to something other than the oil itself. We depend largely on distillate oils in California and they are used at a strength from 6 to 8 per cent on dormant trees. The latest use of oil there is the heavy crude petroleum, 16° to 18°, just as it comes from the wells and is used in the form of an emulsion with soap at a strength as high as 15 per cent. This seems to be the only thing that will control the Italian Pear Scale successfully. Thus far there appears to be no complaint of injury even with the heavy crude petroleum.

MR. H. A. GOSSARD: A number of years ago I conducted some small experiments with oils, obtaining the same results as stated by Dr. Felt. Trees treated in the fall had some of the fruit buds killed, while no injury was done by spring applications. The manufacturers of the oil were quite perplexed and skeptical concerning my conclusions and went to considerable trouble to determine where the trouble lay. They took samples of the water used for diluting the oil and reported that they found considerable sulfur in it. They thought this was the explanation of the adverse result. Referring to spraying mixtures, I prefer to recommend the preparation that is nearest to "fool-proof" of any that I know. If I am writing to an experienced horticulturist, whom I know to be an intelligent sprayer, I use my best judgment in giving a prescription, but when making general recommendations for publication or when writing to strangers, I always want to name the nearest to a "fool-proof" remedy that For this reason I prefer to recommend home-made limesulfur solution where practicable before the oils or the commercial mixtures.

MR. T. B. SYMONS: In the case of peach lecanium the limesulfur will not phase it. We have to recommend the use of an oil mixture, but we state that the application should be made as late in the spring as possible.