JTATE PLANT BOARD 
 
 August 1950 ET-289 
 
 Ifcited States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entomology and Plant Q:uArantlne 
 
 A PORTABLE FIELD GAGE i/ 
 By Marion W. Pedersen, §/ Frank E. Todd, 1' and Frank V. Lie'berman li/ 
 
 Several common disadvantages of portable field cages have been 
 overcome by using plastic screen for the covering and standard electrical 
 conduit for the framework. The utilization of these materials has made 
 it possible to construct a cage that is (l) light, (2) portable intact, 
 (3) easily assembled and taken apart, and (4) conveniently stored. In 
 addition, meteorological factors are not serio\isly modified. 
 
 The cage described in this paper was designed to confine or excltide 
 bees In pollination experiments (fig. l). The dimensions were chosen to 
 fit immediate requirements. Other sizes might be more practical. The 
 cages have held up well through two seasons of use, largely because of 
 sturdiness supplied by rigid corner construction. However, the top 
 screen in some of the coverings used from spring to fall has become 
 brittle. The life of these covers depends upon careful handling so as 
 to avoid creasing. 
 
 The cage covers an area of ZkJ square feet — II3 feet wide, 21-| 
 feet long, and 6 feet high. A plastic screen covering ( 12 by 12 mesh) is 
 supported on a framewoife of i-inch electrical conduit, which is anchored 
 to the ground with steel stakes and wire. A 6-foot zipper is installed 
 in each of the fovir comers to permit entrance, and to facilitate the 
 handling and folding of the cover for storage. 
 
 TJ Cooperative legume seed investigations conducted at Logen, UtaJi, 
 by the Bureau of Plant Industry, Soils, and Agricultural Engineering, the 
 Bureau of Entomology and Plant (Quarantine, and Utah Agricultural Experi- 
 ment Station. Photographs were taken by W. P. Nye. Clarence Austin 
 aided materially in the cage construction. 
 
 2/ Division of Forage Crops and Diseases, Bxireau of Plant Industry, 
 Soils, and Agricultural Engineering. 
 
 ^ Division of Bee Culture Investigations of this Bureau. 
 
 h/ Division of Cereal and Forage Investigations of this Bureau, 
 
The weight of the assembled cage is eraproxiraately II5 po-unds, the 
 cover weighing 32 pounds and the framework 83 pounds. Two men can 
 easily pick it \ip and move it for short distances. 
 
 Comparative tests were made of the relative humidity, temperature, 
 light, and wind movement inside and outside these cages. The results, 
 sho\7n in table 1, indicate no significant differences in temperature and 
 humidity but a significant reduction in light and in wind movement. No 
 differences in alfalfa growth have been observed that could be attributed 
 to a cs^e effect. 
 
 Table 1. Comparison of meteorological conditions inside and outside 
 of 12- by 12-nesh plastic screen cages covering alfalfa. 
 
 Location 
 
 of 
 reading 
 
 Relative 
 humidity 1/ 
 
 Temperature 1/ 
 
 Light 2/ 
 
 Wind iJ 
 
 In cage 
 In open 
 
 Difference 
 
 Percent 
 
 ^3.3 
 
 39.7 
 
 3.6 
 
 70.5 
 
 70.3 
 0.2 
 
 Candles 
 per sq-u^.r© foot 
 
 193 
 -35 !i/ 
 
 M.p.h. 
 
 5.27 
 6.70 
 -I.H3 5/ 
 
 1/ Average of 1 reading in each of 6 pairs of plots taken with a 
 psychrometer. 
 
 2/ Average of 2 readings in each of 8 pairs of plots taken with e 
 photographic meter, 
 
 ^ Average of 20 recidings in each plot of 1 pair taken with an 
 anemometer, 
 
 U/ Highly significant (l^ level). 
 
 ^ Significant (5^ level). 
 
 Construction of Conduit Framework 
 
 The boxlike framework is made from suitable lengths of conduit 
 coupled to welded comer units. Short lengths are cut from standard 
 10-foot pieces with a hacksaw. Two or more pieces must be coupled to 
 form lengths longer than 10 feet, A conduit bending tool is essential 
 for making bends. 
 
Comer units (fig. 2): 
 
 The comer pieces are U-foot lengths of conduit bent at right angles. 
 One of these comer pieces is welded to each end of the corner posts. 
 The 2i-foot "braces, which support the comer pieces, are then welded Into 
 place as shown. A wooden form made to hold the pieces of conduit in 
 place while starting the welds speeds up the operation and assures uniform 
 comer units. Ends of the "braces can be more easily welded if depressed 
 on one side with a ballpeen hammer. 
 
 Sides and ends: 
 
 The upper and lower end pieces are 7"2 feet long. The upper and 
 lower side pieces are I72 feet long (a 10-foot length coupled to a 7^- 
 foot length). 
 
 Cross memhers (fig. 5)* 
 
 Three cross members are used in the top of the framework to prevent 
 the covering from sagging. The center one is a regular 10-foot length 
 attached to 6-foot posts by means of side supports. The other two are 
 made by coupling together a 10-foot piece and a li-foot piece. A small 
 hole is drilled in each end of the 11^-foot cross members for use in 
 wiring them to the main part of the frame. 
 
 Side supports (fig. 3)s 
 
 The connector piece for the center cross member is made by bending a 
 1^-foot length at a right angle. The piece is then welded to the 6-foot 
 post 80 that the bottom of the horizontal arm is level with the top of 
 the post. A small hole is drilled through the post ^ inch from each end 
 and in the same plane as the connector piece. 
 
 Construction of Screen Covering 
 
 The covering is made as follows: 
 
 1. Cut the strips of plastic screen from the rolls. 
 
 2. Sew the strips together in the design indicated (fig. Ua) , using 
 ■|-inch cloth tape to strengthen the seams. Use double stitching. Cotton 
 thread is satisfactory. 
 
 3. Install the zippers. The edges of the screen (c) are folded 
 back for 1 inch and bound between the zipper and 1-inch cloth tape, using 
 a double seam. 
 
 U. Bind the remaining edges (b). Sew 2- inch webbing along the four 
 sides, folding unfinished edges back, A double thickness of canvas can 
 be substituted for webbing. 
 
* k 
 
 5. Install the grommets at Ig-inch interrals along the webbing. 
 
 Assembly and Anchorage 
 
 Although one person can assemble the framework (figs. 5 and 6) and 
 put the covering in place, it is much more convenient for two people to 
 do it together. After both ends are assembled on the ground, they are 
 raised to their upright positions and joined with the side pieces. The 
 center cross member is next coupled directly to the connector piece of 
 the side supports. This U-shaped unit is then wired in place, being 
 fastened to the upper and lower side pieces. Care should be exercised 
 to twist the wire in such a way that it cannot catch in the covering. An 
 auxiliary cross member is then wired in place halfway between the center 
 cross member and each end of the cage. 
 
 After the covering is pulled over the framework the zippers are 
 closed. The covering is then securely fastened to the bottom of the 
 framework by wiring each grommet to the conduit, For some purposes more 
 positive closure may be necessary, in which case the bottom can be 
 banked with soil. Canvas that is to be kept covered for extended periods 
 of time with moist soil shoiild be treated to make it rot resistant. 
 
 Anchorage is the final step. The bottom of the cage is secured to 
 the ground with open-end steel stakes (fig, 3)» These stakes are driven 
 into the ground until the hook comes into place over the conduit. Guy 
 wires from the corner units and side supports are attached to closed-end 
 stakes in the ground (fig. 3)» Guy wires can be placed either inside or 
 outside the cage and have been used both ways satisfactorily. Convenience 
 and local wind conditions should govern the arrangement. The outside 
 anchorage is preferable against strong winds, since holes may form where 
 the wires go through. 
 
 Storage 
 
 Two men can dismantle and store a cage in 30 minutes. The flexible 
 covering may be folded or rolled into a compact bundle. The four corner 
 units partially nest. 
 
Materials aad Cost of Cage 
 
 Item 
 
 Estimated 
 Units Length (feet) cost, wholesale 
 
 Couplings 
 
 Conduit (^-inch galvanized) 
 Comer units 
 Comer posts 
 Comer pieces 
 Corner braces 
 End pieces 
 Side pieces 
 Long length 
 Short length 
 Side supports 
 Posts 
 
 Connector pieces 
 Cross memhers 
 Center 
 Auxiliary- 
 Long pieces 
 Short pieces 
 
 Plastic screen (3-foot width) 
 
 Strips 
 
 Strips 
 Zippers (6 feet) 
 
 Stakes (3/S-inch iron) 
 
 Closed end 
 
 Open end 
 Bpling wire 
 
 Framewoxk 
 21^ 
 
 k 
 8 
 
 16 
 1+ 
 
 k 
 k 
 
 2 
 2 
 
 2 
 2 
 
 Covering 
 
 k 
 k 
 
 Anchorage 
 
 Labor 
 
 Sewing (including webbing, 
 tape, and thread) 
 Welding 
 Cutting and bending 
 
 grommets, 
 
 10 
 
 6 
 li 
 
 10 
 
 10 
 
 li 
 
 3^ 
 22 
 
 1/5 
 1/5 
 
 $ 3.00 
 17.00 
 
 30.00 
 
 U.oo 
 1.00 
 
 20.00 
 l^.oo 
 1.00 
 
 Total $S0.00 
 
Figure 2. --View of upper half of a corner unit. 
 
 Figure 3. --Side support showing welded, wired, 
 and coupled connections. The two types of IJBRARY 
 anchorage stakes are shown at the ^ig^t. ^«£ p^^NT BOARD 
 
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 Figure 4. --Diagram. showing shape and seams of cage covering: 
 a. Double seams with l/2-inch cloth tape; b, 2-inch webbing or 
 canvas with 3/8-inch grommets at 18-foot intervals; c, zipper sewed 
 on 1-inch tape with double seams. 
 
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 Figure 5. --Diagram of 1/2-inch conduit framework for supporting cage: 
 a, welded joint; b, watertight coupling; and c, wired joint. 
 
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UNIVERSITY OF FLORIDA 
 
 3 1262 09242 9330