TATE PLANT BOARU
ET-168 December 1940
United States Department of Agriculture
Bureau of Entomology and Plant Quarantine
A MOBILE SAMPLE-CARRYING RACK
By H. W. Rusk, Division of Insecticide Investigations
For a number of years fruit samples from apple orchards
have been oollpctd throughout the growing season and brought to
the chemical laboratory (for residue-deposit analysis) in inexpen-
sive paper bags. This practice has resulted in the physical removal
of some of the residues, owing to contact with the bag surface
during travel and subsequent handling preparatory to analysis.
The trailer rack herein described was constructed to carry
44 individual samples of 25 fruits each. The fruits are impaled on
12-gauge pointed steel wire pins 4 inches long. The pins bearing
the fruit are placed on the sampling boards and are finally trans-
ferred to the sample-carrying boards, which are then slid into their
proper place in the rack.
The method of collecting fruit on wire pins and mounting them
on boards or long sticks is not new; as early as 19321 this pro-
cedure was used by the Vincennes laboratory of the Division of
Fruit Insect Investigations for collecting fruit from field spray
plots for artificial infestation under controlled laboratory
conditions. At that time the sticks bearing the fruit were placed
in slotted drawers of large wooden boxes, which were brought in
from the field by truck. From 1936 on, a four-wheeled trailer
bearing a specially constructed rack has been in use by the Division
of Fruit Insect Investigations for carrying samples for biological
testing from the orchard to the laboratory.
It will be seer, therefore, that the trailer rack herein
described is merely an adaptation of a previously devised rack,
the alterations in design being made in such a fashion as to make
1 Lathrop, F. H., and Sazama, R. F. 1932. A laboratory-
field method for the study of the efficiency of codling moth
sprays. Jour. Econ. Ent. 25: 83-96, illus.
2 Steiner. L. F. 1939. The laboratory-field method for
testing codling moth insecticides. U. S. Dept. Agr., Bur. Ent.
and Plant Quar., E-488, 10 pp. (multigraphed), illus. September
it more suitable to the sampling for chemical analysis It permits
the placing of an entire 25-fruit sample on a single, board. The
boards are of a size that will allow them to accommodate 25 fruits
up to 2 inches in diameter. For larger fruit it will be necessary
to space the holes for the wire pins a little differently, and the
number of fruits per board will have to be reduced.
The trailer rack was constructed according to the plans
given in figures 1 and 2. Figure 3 shows the truck and trailer
ready for travel from the orchard to the laboratory. Figure 4 shows
the trailer open and ready to receive the samples. In figure 5 a
sample-carrying board has been mounted on the side of the rack to
illustrate the way in which each stratum sample is placed in it.
Directly below it are shown the sampling boards with their respec-
tive fruits ready for transfer to a sample-carrying board. In
position from left to right it will be seen that 7 fruits are taken
from the top stratum of each tree, 10 from the middle stratum, and
8 from the bottom stratum. By this placement it is possible to
conduct studies of residue loads on either the entire tree or
sections of a tree. Figure 6 shows a view of the rack with some of
the boards filled with fruit and in place.
The trailer itself is a small two-wheeled unit consisting of
chassis, springs, axle, roller-bearing 16-inch wheels, and trailer
The bottom frame illustrated in figure 1 was bolted directly
to the trailer chassis in several places with 3/8-inch carriage
bolts of suitable length. Flat washers and lock washers were used
in all cases to prevent the nuts from working loose.
To prevent the sample-carrying boards from jumping out of
their grooves during transit, it was necessary to use square-bend
screws 2 inches long with i-inch bends. One screw inserted in each
runner about 10 inches from the front of the rack was found to be
sufficient to prevent any jumping of the boards. The screws were
run down until the projecting bends were about 1/8 inch from the
The sides of the trailer rack are covered during transit
with curtains of automobile topping material. These curtains
contain a piece of strap iron inch wide and 61 inches long, which
is inserted in a hem in the bottom of the curtains to weight them
down. The sides of the curtains are folded around the front and
the back of the trailer and secured in place with automobile curtain
snaps. During the sampling the curtains are rolled up to the top
of the rack and held securely by cloth straps.
As a safety measure a combination stop light and tail light
was mounted at the left rear of the trailer rack. Two-wire cable
with a detachable coupling was used, the two circuits being grounded
to the trailer chassis, which in turn grounds to the truck chassis
through the hitch.
A list of lumber necessary for the construction of the
trailer rack is given below. It should be noted that all dimensions
of lumber are full measure, in which case a piece listed as 2 by
4 inches is actually that size and not a standard "2 by 4" which in
reality is 1- by 3- inches.
2 2" x 4" x 60" Bottom frame
1 2" x 4" x 52" Bottom frame
2 2" x 6" x 42" Bottom frame
10 2" x 2" x 53" Side posts
2 2" x 4" x 53" End posts
3 2" x 2" x 60" Side ties. middle ridge tie
2 1" x 2" x 42" End ties
6 2" x 2" x 56" Cross runner stops
5 1" x 4" x 56" Cross runner rests
24 1" x 4" x 20" Runner supports
20 1" x 10" x 20" Runner supports
10 1" x 8" x 20" Runner supports
4 1" x 6" x 20" Runner supports
88 1" x 1" x 20" Runners
1 42" x 60-" x !" 3-ply veneer top
1 42" x 60" x L" 3-ply veneer bottom (notched to fit)
2 42" x 53" x T" 3-ply veneer ends
44 11" x 10" x 20" sample-carrying boards (white pine or other
3 I" x 7" x 13" sampling boards
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Figure 5.-Method of placement of fruit.
Figure 6.-Rack partially filled with fruit.
Figure 3.--Truck and trailer ready for travel.
Figure 4.--Trailer open to receive samples.
UNIVERSITY OF FLORIDA
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