Walk-through fly trap works well for organic grazier

by Allan Nation

WILLOW SPRINGS, Missouri: In 1998, when Jerry Fry decided to apply for Organic Certification, nonchemical fly control was one of the items on his list of problems to be addressed. The basic idea of a walk-through fly trap is to create a closed passage the animals must walk through several times a day. When they walk through, canvas strips brush against them, wiping the flies off. When the flies take flight, they go toward the light, but a screen blocks their way. After landing on that screen, they walk around looking for a way out. Eventually, they find a pencil-sized hole and go through it. Once on the other side, they are in the trap and are unable to get out.

After ordered plans for a walk-through fly trap from the University of Missouri Outreach and Extension Publications Center, which enabled Jerry and his neighbor to built it in about four evenings. The cost was a little over $275. Jerry was looking for a portable system, so they put skids on the bottom. If the fly-trap is built to specifications, it is rather heavy, but can still be moved with a 4-wheeler.

Jerry uses strip grazing all the time, moving the fence twice a day. For example, twenty cows might get an area 100 by 15 yards twice a day (of course that amount varies, "depending on the situation"). Normally, Jerry first puts up the next forward fence, then lowers the previous forward fence, allowing the cattle to graze toward the new forward fence.

Next, he hooks a chain to the Fly-trap and makes a U-turn with his 4-wheeler, moving the trap to the fresh grass strip that was just opened. Next Jerry puts the old front fence back up (it is now the back fence for the new 100 by 15 yard area).

He then runs a wire from each side of the trap to the forward and backward limit fences. The trap is now sitting in the middle of the newly allocated 100 by 15 yard area and the cattle must go through it to get from one half of the new allocation to the other. Jerry normally has the water on one side of the trap and the shade or minerals on the other, but that is not always necessary.

With a new group of animals, Jerry takes all of the hanging strips and side panels off of the trap and sets it in the paddock, near the water, to get them accustomed to it. After a day, or so, he uses electric wires to force them to go through the trap to get to water. Once all are going through it, he starts adding the side panels. Next, he starts adding the hang-down-strips a few at a time. When a new group of animals join a group already using the trap, Jerry just lifts the hang-down-strips for a day, or so to let them learn from the others.

When it rains, or if the ground is wet, Jerry does not use the trap. The cattle will tear up the ground going through the trap over and over again. One or two days without the trap is not a problem. If you do not move the trap every day or two, they will wear off the grass even on dry ground. Jerry said, "If I were in a area that is often wet, I might try putting a floor in the trap to keep the cattle off the ground."

Jerry puts a cattle panel on both inside and outside walls, to keep the cattle from brushing against the screens and damaging them. They will damage anything they can rub against.

Rather than the canvas strips, called for in the U of MO Plans, Jerry uses burlap bags. They allow him to put diatomaceous earth (DE) in the bags. When the cattle rub under the bag, the DE dust is deposited on their backs. A nonorganic operation could use chemical fly dust, but it is not necessary. The bags alone will take care of the flies.

Jerry's trap does not work on horse flies. U of MO Guide #G 7013, Protecting Cattle from Horse Flies, has plans for a small horse fly trap. Jerry has not built one, because horse flies have not been a problem for him.

Jerry said, "North Dakota University Extension Service has a publication, 'A Walk-through Fly Trap to Reduce Horn Flies on Pastured Cattle.' Their trap is smaller (and probably cheaper to build) than the one I have, but it seems a little light for a portable system. It should work well if it were going to be in a fixed position. I suggest anyone planning to build a trap review the NDSU publication, prior to building one like mine."

According to Jerry, the trap should be put in service early in the spring, prior to flies becoming a problem. Last year, he had a new stocker calf develop pink eye, prior to flies becoming a problem. Before he could bring his trap into service, and train 63 new calves, another came down with pink eye. This group developed the habit of ducking their heads under the burlap bags, so Jerry made a slit down the sides of the bag in the middle, so that one bag hung to the ground.

At the entrance/exit to the trap, a bag should be hung which does not touch the back of your animals. It helps darken the inside of the trap, steering the flies to the sides, but does not brush off the flies as they enter the trap.

Jerry said, "I am very happy with my trap; I do not have a fly problem. Having said that, I also give my mobile chicken house some of the credit. I have a small house, mounted on a boat trailer, that holds 30 birds. The chickens tear up the cow pies and eat the fly larva. Consequently, we are not only attacking the flies directly with the trap, we are also interfering with their reproduction cycle with the chickens."

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