UBRARY 5TATE PLANT BOARD lb7 1943 ir-20d UNITS) STATES DS'ARIIUnT OP ACSICULTURS Agricultural Research Administration Buraau of ^itomology and Plant Quarantine A LABORATORI APPARATUS AMD PROCJBDURE FOR TESTING AQDBOUS SPRAY SUSPMSIONS AS INSBSTICIDES 37 £• R. SfeGovran and S. L. Hajer DlYiaion of Control Inrestigationa There are two general types of laboratory apparatus for applying spray suspensions. In one type the spray is applied to an uneren surface such as a potted plant. In the other type, de- scribed belov, the suspension is applied to a relatirely smooth surface such as a leaf or section of a fruit. The spray is eren- ly distributed, preferably as small drops, to prerent large accu- mulations of the suspended material from foxming in certain areas before the spray has dried. If a suspension is sprayed to form a uniform distribution of drops of the same rolume closely packed together b\it not coalescing, a relatlYely uniform deposit should be obtained if each drop is considered as a unit area* Therefore, if the area consumed 1:^ the insect is greater than the area cov- ered by a single drop, it is probable that the insect will ingest a proportionate dose of insecticide. This may not be true, ho»- erer, if the insect consumes a smaller area, because within an individual drop of spray the deposit may not be uniform, owing to the settling of the insecticide within a drop and other factors* SPRAT AND SETTUNG CHAHBSS The spray and settling chambers consisted of a cylinder «r tower (fig. l) 6 feet in hei^t and 2 feet in diameter. Light was admitted through a lO-ineh-sqaare eellwloid window (B) in the re- movable wallboard top (A) of the tower. The floor (G) of the spray chamber (C) was 5 feet from the top and was made of half- inch-mesh galvanized screen. Below this screen was the settling chamber (R), irtiich stood on the floor of the laboratoxy (T). The intake of "a blower (S) for exhausting the contents of the'tower to the outside of the building opened near the floor. The inner surface of the spray tower was ef linelevm aal the outside cover- ing of building paper. The two surfaces were separated by a 1- inch air space for insxilation. A removable door (F) 6 inches wide extended 10 inches above and below the screen*'floor (G), and two 4-inch-square observaticHi windows (E) were located 15 inches above the screen floor. The tower was supported b7 passing through and being securely attached to a table (j^). I SPRAIBl The sprajv (K) was a modified air brush aanufactured for applying palixt. Ths'liqaid orifice was 1.75 nn. in diameter and was KLrrounded bj the air oxlfiee. The sprayer operated as an atoniser and drew the liquid up through a straight copper tube (L) about 4 ■»• in dianeter. The sprayer, as purchased, had a bend and a flnll chamber in the liquid line, but it was replaced by the strai^t tube because the larger particles of insecticide collected near this hmA and also in the small chamber* The Bpnjmr was moxuited below the screen floor so that it discharged upward at about the lerel of this floor. Three setscrews per^ mitted accurate adjustmait of the direction of discharge. Just belew the sprayer was a container (M) for the spray suspension, which was held in place by a threaded Jar top. From this posi- Hen the liquid was raised Tertically throu^ the sucticm tube and sprayed out so that settling in the tube was practically eliainated. Whea the air pressure was shut off, the material in the tube fell back into the container*. Air pressure at 50 pounds per square inch operated the sprayer. This could be turned on and off at a yalve (O) located outside the spray tower. AGITATION Of SPRAI The agitator used in preliminary tests gave variable d»- peaite. For wxample, chemical analysis revealed that a fine fraction of paris green deposited Ik, a medium fraction 26, and a coarse fraction 70 micrograms per square centimeter, when equal weights of the three fractions were added to 100 ml. of water* ^ The agitator adopted gave deposits of 16. 9» 17*2, and 18»2 aicrograBS per square centimeter for the fine, medium, and coarse fractions, respectively. These figures show some increase in deposit with increase in particle size, possibly due to the •notion pipe of the sprayer opening near the bottom of the spray container. To obtain unifom deposits of paris green, the amount of each fraction used was adjusted to give the desired deposit* A« many experiiaeatal materials that are tested as insecticides wettle or rise rapidly when suspended in water, the data given d«aonstrate that the •ffieiancy of the agitating a^ ttem may r«e- terMine the deposit of insecticide obtained* V The amthora mish to thank C. 0. Cassil, C. M. Statith, and others in the Dlviaion of Insecticide Investigations for preparing these fractions of paris gz>een and the chemical analysis given above, and also for materials and suggestions on procedure used in determining the deposits given under "Unifont- Ity of Deposit." - 3 - The spray suspension was agitated by a rubber blade which rotated in a horizontal plane near the bottom of the container (M). This blade v;as mounted on a vertical shaft (j), which was driven by a flexible shaft (l_) from a variable-speed motor (H) mounted out- side the spray tower. The agitator speed was adjusted to keep the materials suspended without forcing air bubbles into the spray sus- pension. UNIFORMITY OF DEPOSIT Following preliminary tests to center the spray discharge, several applications were made on six pairs of glass slides 8 by 10 cm. arranged in two concentric circles 10 cm. apart on the floor of the chamber. The average deposit on the slides in the inner circle was 22 percent greater than on those in the outer circle. To obtain a uniform deposit on leaves, after half the spray suspension had been applied, the position of the leaves was re- versed before the other half was applied. The leaves were then turned over and the other side was treated in a similar manner. To check further on the uniformity of the deposit at dif- ferent positions, spray applications were made on six glass slides arranged on the screen floor in a single circle' equidistant from the center and the outside wall. After six to nine replica- tions of each of three fractions of paris green — fine, medium, and coarse— the average deviation from the mean deposit of all frac- tions was 7.2 percent, and the average individual variations from the mean deposit in each application ranged from 1.9 to 14.2 per^ cent. As these tests varied both in the concentration and the particle size of the insecticide used, they appear to give some idea of the variation that might be expected in this method. Casual observations had shown that near the center of the spray floor and near the wall the deposits were not uniform. PREPARATION OF LEAVES FOR SPRAYING Flat leaves, such as those of certain varieties of turnips and beans, were cut and the petioles inserted in vials of vraiter through one-hole stopjers. The petioles fitted in the stopper tight enough so that air entered the vials as the leaf withdrew the water but the water did not leak out (fig. 2, A). The leaves with the vials attached were placed on wooden paddles of approx- imately the same shape and size as a single leaf. The vial was attached to the paddle with rubber bands,) and the leaf blade was held in a horizontal position by the points of pins that extend- ed up from the paddle. V^hen the leaf was turned over to spray - 4 - the other side, the deposit on the sprayed surface vreis not material- ly disturbed, as it was not heavy enough to drain dovm the pins. .Vhen the exact area eaten by bean beetles was desired, the under surface of the bean leaves was covered with a piece of flannel. The nap of the flannel and the pubescence of the bean leaves held this cloth firmly in place, preventing the insects from feeding on the lower surface. OPERATION OF TH2 SPRAY APPARATUS Leaves were placed on the screen floor in a circle equidis- tant between the spray nozzle and the wall of the spray chamber. When chemical analyses of a deposit were desired, two or more glass slides, 8 by 10 cm., were laid between the leaves. The door was closed and the vent through the exhaust blower was opened but the blower was not started. The valve in the air line was opened, and the spray stream rose in the chamber and fell back onto the leaves on the screen floor. The screen permitted the spray and air to pass into the settling chamber below and from there to the out- side with little interference, and thus reduced the formation of eddy currents which would tend to disrupt the uniform deposition of the spray. When half the amount of liouid that would produce the desired deposit had been sprayed, the air was shut off and the spray allowed to settle for 1 minute. The top of the tower was then raised slightly and the blower run for 30 seconds to remove any spray that might have settled unevenly when the leaves were being moved, and also to reduce the health hazard to the operator. The position of the leaves was then reversed. The quantity of spray suspension used was replaced in the container and the opera- tion repeated to finish the spray deposit on one surface of the leaves. The leaves were then turned over and the other side was sprayed, except when one side of the leaves was covered with cloth. IKTFESTING THE SPRAYED LEAVES Either Mexican bean beetles or southern armyworms were used as test insects. ViTien Mexican bean beetles were used, a dry sprayed bean leaf with the vial of water on its petiole was placed in a 6-inch Petri dish together with 10 to 20 adults or larvae, which were confined by a screen cover. Mortality counts were made after 24, 46, or 72 hours, and subsequently at 48- or 72-hour intervals until the mor- tality rate approximated that occurring among insects on untreated foliage. The treated leaves v.ere replaced by fresh untreated ones after 48 or 72 hours and subsequently as the insects needed food. The leaf surface consumed was measured by comparison with milli- meter-ruled paper. - 5 - When southern annyworm larvae were used as test insects, turnip or collard leaves were sprayed. As the southern armyworm tends to be cannibalistic, especially when poisoned, the larva* were confined individually (fig. 2, B-F)« The blade of a sprayed leaf was laid on l6-mesh screen tacked to a 12-inch length of 6- inch board. The vial was fastened to the board with a rubber band. A screen cage 2 l/A by 6 1/4 by 3/4 inches, divided into 5 sections 2 1/4 by 1 1/4 inches, was placed on each side of the midrib of the leaf. The ends of the screen wires that formed the sides and par- titions pierced the leaf blade and made close contact with the screen attached to the board below the leaf. The sides of the cages had been treated with an acetone solution of celluloid to add rigidity and also to separate the larvae more con^)letely. One fifth instar was enclosed in each section of the cage, which was then placed on the leaf and secured with wooden strips and rubber bands. Mortality counts were made in the same manner as for Mexi- can bean beetles. SUMMART A laboratory apparatus and a method of applying spray sus- pensions are described. The spray stream is discharged vertical- ly upward and the drops of spray fall back on the surface to be treated. This method gives a relatively uniform deposit of spray material, and a nimfcer of excised leaves can be treated simultan- eously. A cage for confining a number of larvae individually on an intact leaf is described. ^J^'O^ Digitized by the Internet Archive in 2013 http://archive.org/details/laboratoryapparaOOunit Figure 1. — Diagram of spray tower. See pages 2 and 5 for names of parts that are lettered. Figxjre 2, — Caging larvae individxially on a sprayed leaf. A, Leaf in position to be sprajredj B, wooden strips and rubber bands to hold cage on leaf; Cj cage with five larvae, ventral view, ready to invert and place on leaf in position Dj E> second cage already in place; F, base- board with leaf and one cage in place. iiiil J'