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SUMMARY OF FIVE YEARS WORK ON SPRAYING
M. P. ZAPPE AND E. M. STODDARD. In order to show the relative merits of spraying and dusting as determined by the results of our experiments during the years 1920 to 1924 inclusive, we here present a summary in which are brought out the points that seem to have been demonstrated in these particular experiments. We have included some other interesting features in regard to the occurrence and control of insect and fungous pests.
In the preparation of these data we have scored 564,675 apples, chiefly of four varieties, McIntosh, Greening, Gravenstein and Baldwin, in four different orchards in the vicinity of New Haven.
The following table gives the average results in per cent. for all the spraying, dusting and checks on all varieties for the five years indicated above. In this table "other fungi" includes sooty blotch, fruit speck, rust, black rot and bitter rot. “Other chewing insects” includes the various chewing insects other than are listed which attack the fruit of apples.
Codling chewing Treatment Good Scab Fungi Aphis Red Bug Curculio Moth insects
% % % % % % % % Spray... 68.6 14.7 6.05 10.0 1.3 17.7
1.8 Dust. 41.4 30.2 28.4 10.7 2.6 21.8 1.4 4.7 Check... 12.2 40.5 34.8 9.7 12.8 48.6
9.8 It would seem from these figures that dusting is practically as good as spraying for the control of red bug, curculio, codling moth, and other chewing insects, but in the control of fungi there is a wide variation in favor of the spraying. Aphids have not been controlled by either treatment, in fact the checks show the least amount of injury. It is evident that aphids and curculio cause the greatest amount of insect injury on treated trees and are the most difficult to control.
Scab took the largest toll of all the fungi, with sooty blotch and fruit speck ránking next, these latter making up the greater part of the injuries listed in the table as "other fungi.” Rust, black rot and bitter rot are so rare as to be negligible on the varieties included in the orchards in this study.
In the study of the data it was found that scab was the least prevalent in 1920, which year had the largest amount of rain of all of the five years, and in 1921-22-23-24 which had normal rainfall or less than normal, the per cent. of scab was higher by 50 to 70%. These computations were made on the data from check trees which represent the actual amount of scab present in the orchard, and were not influenced by variations of treatment. A study of the weather conditions during April, May and June of
these years showed that in 1920 the periods of high humidity were very short, the per cent. of humidity dropping immediately and sharply after a rain, while in the other years the humidity dropped slowly after rains, sometimes lagging over three or four days, and very light rains were often accompanied by high and sustained rises in humidity.
Further study will be necessary to establish this apparent relation to per cent. of humidity rather than actual rainfall, but it would seem that better results from spraying would follow if it be done before or during sustained periods of high humidity rather than before rains. It is our belief that a close study of the weather conditions is a safer guide for the orchardist to follow than information as to time and duration of spore discharge, because it is safe to suppose that sufficient spores will always be discharged to cause a damaging amount of infection if weather conditions are suitable for such infection and if the trees are protected during optimum periods for infection the desired control will be obtained. Inability to predict these conditions accurately will necessitate spraying a certain number of times as insurance, timing them as near as possible to give maximum protection.
Our data show that McIntosh is the most severely attacked by scab of the varieties used in the experiments, but the amount of injury from all other insect and fungous pests is considerably less than on the other varieties. Baldwin is the least susceptible to scab but much more susceptible to sooty blotch and fruit speck, and in most cases shows more curculio injury. Gravenstein is most severely injured by aphids of all the varieties observed.
TESTS OF INSECTICIDES FOR THE CONTROL
OF THE ASIATIC BEETLE.
M. P. ZAPPE AND P. GARMAN. This insect has caused considerable injury to lawns in the western part of the City of New Haven, in the vicinity where the adults of this insect were first collected on July 16, 1920. In some cases sections of lawns equivalent to 60 square yards and smaller have been ruined by the larvae or grubs, as they are commonly called, which devoured the roots of the grass. Where the infestation is heavy, the turf may be rolled up like a carpet. Many of the property owners have spaded up the infested sections, collected, and killed all the grubs they could find, afterwards reseeding their lawns. During the summer of 1924, tests of several insectides and methods of their application were made to determine which of these are the most practicable and efficient in controlling this insect in the larval stage in lawns. So far as we know, this pest has not been troublesome in gardens, with
the exception of one case where a few grubs were found in a strawberry bed near a badly infested lawn.
Previous accounts of this insect in Connecticut have been published in the Report of this Station for 1922, page 345, and for 1923, page 291.
Calcium CYANIDE. This material was used on lawns in several tests at strengths varying, from four to six ounces per square yard. It is a coarse dust containing from 40 to 50 per cent. of calcium cyanide, and is very poisonous, not only when taken internally, but when the gas is inhaled. The soil where all tests were made was a type of light sandy loam.
Two plots were laid out on an infested lawn; one containing 20 square yards was treated with calcium cyanide at the rate of four ounces to the square yard, the other containing 60 square yards was given a dosage of six ounces per square yard. The cyanide dust was applied to the lawn as evenly as possible with a hand fertilizer drill, after which the ground was thoroughly wet down with a garden hose to wash the cyanide into the soil. (See plates XXIV, b and XXV, a).
Before applying the cyanide, a square foot of soil was dug up and all larvae were counted. There were 63 larvae in this square foot of soil, most of them being in the upper three inches among the grass roots, although a few were found six inches deep. Other sections were also dug, and found to be similarly infested.
Prior to our treatment of this lawn, the owner had spaded part of it and what sod was left had been turned under, so that it was buried four or five inches deep. The treatment was applied on May 14. On May 19, many of the grubs were dead in both plots, but in that portion of the lawn which had been spaded, before treatment, most of the live grubs were in the sod which had been turned under, and were too deep to be killed by the cyanide.
A good kill was obtained on that portion of lawn which had not been spaded, and practically all of the dead larvae were in the first two inches of soil; below this depth there were quite a number of living ones. All grass on the treated portion of lawn was badly burned by the cyanide.
Both plots were treated as one on May 31, with calcium cyanide, using about five ounces per square yard. This time the ground was spadeci after the application, then immediately treated again, and watered thoroughly. On this date the wind was quite strong and blew some of the cyanide dust upon rose bushes, Spiraea and Weigela. Nearly all the leaves on the rose bushes were so badly injured that they dropped off, and the Spiraea and Weigela were also injured, though not so badly as the roses. The roses were not killed, as they produced a new set of leaves in a short time.
A few days later an examination of this plot was made and it was found that about a 100 per cent. kill had been obtained. On May 19, several small wire cages containing three larvae and a small piece of sod each, were buried in small holes in the ground at the following depths from the surface; one hole with two cages, one three inches, the other six inches deep; another hole with cages at five inches and another seven to nine inches deep; . and one hole with cage four inches deep. One ounce of cyanide was then placed in a hole eight inches deep and six inches from the holes containing the buried cages of larvae, and covered with soil.
An examination made a week later gave the following result:
No. Dead 3
Not treated On another lawn, a plot one yard square was selected and holes made with a crowbar about six inches deep and 12 inches apart; each hole was dosed with one-third ounce of calcium cyanide. After the cyanide was put into the holes, they were filled up with earth. Another plot of two square yards was treated in a similar manner, except that the holes were made two feet apart and were dosed with one ounce of cyanide. An examination of the plots a few days later showed practically no kill of larvae on either plot.
A similar test was made at another place, using one ounce of calcium cyanide, placed at the bottom of a hole four inches deep and three inches in diameter, made by a sod cutter. The cyanide was covered with soil. Other holes the same size and shape as the cyanide hole were made at varying distances from them and an Anomala larva in a small wire cage buried in each hole. Eight holes with a larva in each one were made near the hole containing the cyanide. The cyanide and larvae were placed May 28, and examined June 11.
*No. Inches from
0 It may be seen from the tests that the application of calcium cyanide by the hole method was not a satisfactory method of
Two holes at each distance.
control for Anomala larvae. This method has the advantage of not killing the grass. By the broadcast method of application, a good kill of larvae resulted, but the grass was very badly burned. The men broadcasting the cyanide experienced a disagreeable dryness and hoarseness of the throat as well as headaches. More serious effects might be felt if operators were exposed to the action of the cyanide for a longer time. For these reasons it was thought best not to recommend this material for general public use in the control of this insect.
SODIUM CYANIDE. This is the ordinary cyanide used in combination with sulphuric acid and water for the fumigation of houses, greenhouses, warehouses, etc., for the control of various insects infesting places that are or can be made air tight. For the control of Anomala orientalis, a certain amount of cyanide was dissolved in water and sprinkled on the lawn to be treated, afterward wetting down thoroughly with water from a garden hose.
Three plots were treated with sodium cyanide, using one-eighth, two-eighths, and three-eighths ounces per plot of one square yard. Cyanide was applied as described in the above paragraph. A few days later the plots were dug up and all larvae collected, with the following result:
12 Further tests with sodium cyanide were conducted by burying five larvae in a wire cage in the center of a plot one yard square in area. The cyanide was applied as before, dissolved in water and sprinkled on plots with a watering can, then watered with garden hose.
0 Grass partly killed Three-fourths 0 5 Grass all killed One
0 5 Grass all killed Another plot of 24 square yards was treated with sodium cyanide using one ounce per square yard dissolved in water and applied to the lawn in the usual manner. Treatment was made on June 11, and on June 17, the plot was examined and approximately 90 per cent. of the larvae had been killed. Most of the larvae that were left alive were found rather deep in the soil. The grass on this plot was all killed.
Other insecticides were tried on a small scale to determine their effect upon Anomala. Mercuric chloride was tested on a plot of 11 square feet, using one-tenth ounce of this chemical.