Question of the Week
Answer: I am pleased to provide you with information on gopher control.
An important first step in any pest management strategy is to understand the life cycle, burrowing and tunneling habits, and damage patterns of the rodents that cause problems on your farm. Then you can design a systems-based approach to managing them.
Gopher management, like any rodent control, will be a continuing effort, especially at key times each season. Pocket gophers live 3-5 years. Females bear 3-5 litters of 2-10 young per year (7). It is probably unrealistic to expect to fully eliminate the problem.
To complement the management options I have outlined below, more information resources, products and services on non-toxic rodent control are available from Gophers Limited. Thomas Wittman includes very thorough PowerPoint presentations (as well as a schedule of where and when he is presenting) on his website that you can view by clicking on the presentations menu. An article on gopher control on organic farms is referenced at the end of this letter.
Depending on the wildlife that lives in your region, many types of predators may be able to help reduce rodent populations. A healthy population of wild predators may include owls, snakes (such as corn, rat and gopher snakes), hawks, great blue herons, weasels, bobcats, coyotes.
Domestic dogs and cats may also play an important role. They do need to be carefully managed, however. Domestic cats will readily prey on small birds that you may find desirable on your farm.
Rat and corn snakes on the mainland U.S. feed on rodents, such as mice, rats, and squirrels. Please note that both species also feed on small birds, so that chicks and eggs might be at risk as well as rodents. Gopher snakes do eat gophers, but do not represent an adequate control measure by themselves. Important and helpful as they are, they are not voracious. A gopher snake eats one gopher about every 6 weeks (7).
Of particular interest as an adaptable predator is the barn owl. Barn owls are very efficient predators. More than 95 percent of the diet of barn owls usually consists of small mammals, mostly rodents. However, in some studies substantial bird remains have been found. According to Colvin (2) each adult barn owl may consume about one or two rodents per night; a nesting pair and their young can eat more than 1,000 rodents per year. Dietary studies from California and other states show that a barn owl consumes on average 50 to 60 grams of prey per day (0.11-0.13 pounds per day, 40-48 pounds per year). The actual species consumed depends on the species abundance and availability in the area.
Many farmers have a great deal of success in attracting barn owls by putting up nest boxes, as barn owls will readily use man-made nest boxes. More detail on design and placement is enclosed at the end of this letter. It includes some specifications for constructing barn owl nest boxes and some considerations for building and mounting them. It’s clear that there is more than one way to build a barn owl box.
One animal’s predator can be another animal’s prey. Great horned owls can eat barn owls, so think carefully about placing barn owl boxes where their inhabitants may be vulnerable to larger predators.
Trapping, Habitat Reduction, and Physical Barriers
Many if not most organic farmers rely on trapping for some degree of control. Trapping can be very effective when used with persistence, skill, and appropriate type of traps. To be most effective, trapping must be done daily, especially at critical times in the cropping season and key seasons (usually early spring) in the life cycle of the rodent.
Many types of rodent problems may be minimized by making the farm and areas around farm buildings less hospitable to them, removing shelter and potential food and irrigation. There are many kinds of gopher traps on the market. Each type of trap has its advantages. Many farmers develop personal favorites that they are comfortable using. Some commonly used traps that are simple and effective against gophers include the cinch trap, Macabee "old reliable," and black hole traps. Most garden supplies and stores that carry wildlife control supplies will carry these traps and have instructions about how to use them.
Branch name traps tend to hold up better to wear and be easier to set than imitations. Most of these type traps are based on the idea that gophers try to fill holes in their tunnels, and trap the animal in the process of pushing dirt toward a hole. The advantage of the cinch trap is that you can see whether or not the trap has been sprung while it is still in the hole. This saves time when you set several traps and need maximum efficiency in terms of time spent per trap. The cinch trap is the head-and-shoulders favorite of gopher expert Thomas Wittman. They require less digging (another time saver); they can sometimes be pressed right into a fresh tunnel mound.
The disadvantage in my experience is that they are a bit tricky to set. They can hurt one’s hands (or a pet’s nose or extremities) when they spring unexpectedly. Gloves are advised, not because they make any difference in the rate of success in catching gophers, but because they do protect one's hands. Once placed, a large flower pot or bucket can be inverted over the set trap to protect pets and other animals that may be nearby.
The cinch trap model designed for moles has slightly smaller jaws than the gopher model. It is actually more effective in catching gophers than the gopher model, as it fits more easily into the tunnels. The jaws of the gopher model are really too large to fit in the tunnels of pocket gophers — at least in the Western region.
A few tips for setting gopher traps:
- If the mound is more than a few hours old (at all dried out as opposed to fresh and moist), I don’t bother setting the trap; the gopher is long gone from interest in that particular tunnel opening. Instead, I watch the surrounding area over the next day or so until I see a fresh mound, and then set a trap immediately.
- To find the tunnel in which to set a trap, look for the small crescent arch on one side of the fresh gopher mound. I open the tunnel in that direction away from the rest of mound (think about how the mound was formed; the gopher is down in the tunnel, pushing dirt out with its hind feet — opposite the direction of where the tunnel is heading).
- Use a strong-bladed Japanese knife called a Hori Hori (available from Gophers Limited — see website below — and Harmony Farm Supply in Sebastopol, CA). The Hori Hori is approximately the diameter of a pocket gopher tunnel, and provides sufficient length to explore whether the tunnel you have found will accommodate a trap. Gopher tunnels often take surprising twists and turns. Open it and dig out just enough soil until you can place a trap easily.
- To increase the ease of finding and removing the trap, secure a strong but flexible wire to the trap, and attach it to a stick that remains outside the tunnel.
- You need not ever bend any of the metal parts. When you first go to set a Macabee trap, you may wonder, “how do I get that little wire in place in that notch?” When you squeeze the two springy parts of the trap together to open its jaws, the wire trigger can be brought easily from underneath, through the wider opening you have just created, and to the notch where it need to be to set the trap.
- Use two hands to open the trap. This makes it easy and minimizes the chances that you will catch your hand in the sharp metal barbs of the jaws if something slips. I use bare hands for these, as it gives me greater dexterity and I am used to it. Using both thumbs, I press the trap open. Then holding it firmly, I use my fingers to place the wire trigger in the notch.
- Place traps in one tunnel or two? I have had success both by setting a single trap in the tunnel that leads to the surface mound, and also by digging a bit further to set a pair of traps — one in each direction in the main tunnel. Both are good strategies, with the latter working better unless the mound is extremely fresh.
- Place the trap carefully in the tunnel. You can hear or feel if it springs prematurely as you place it. Sometimes it takes a couple of tries, re-setting the trap in between.
- People debate whether to leave the hole open or to cover it over. While the theory that a gopher will come close an open hole is a sound idea, I have had consistent success by covering the hole. I use a small piece of cardboard, a board, or simply a handful of nearby vegetation to prevent too much dirt from falling directly on the trap. (Sometimes it seems that something tasty — like the top of green bean plant they just cut off — may attract the gopher right into the trap.) Then I seal the hole with dirt. The fine, loose dirt form the gopher mound itself makes this easy.
- Check your traps regularly—usually first thing in the morning (or morning and evening if you are really dedicated to reducing your gopher populations). If you have not caught anything in 24 hours, you probably won’t. Remove the trap (keeping it dry will reduce rust and prolong its life), fill in the hole, and watch for new activity.
Another option for smaller areas: a strong piece of heavy duty rebar about two feet long can be used to follow, collapse and fill tunnels over a longer distance. Gophers dig many new tunnels to find new food sources, but they will reuse tunnels that are useful and desirable for a long period of time. This rebar disturbance to their tunnel system may be sufficient deterrent to the gopher to return to that area — at least for a while.
Many types of rodent problems may be minimized by making the farm and areas around farm buildings less hospitable to them, by removing shelter and potential food sources. However, in the case of gophers, which feed on plant roots, this is not possible, though plants that are distasteful to gophers can be planted, as noted below.
Physical barriers to invasion or access to food, such as fences, wire baskets, or even trenches and irrigation can help to limit rodent populations. Any barrier must have holes that are small enough that gophers cannot pass through. If you use wire, be sure to get gopher wire or even aviary wire. Chicken wire has openings that are large enough to allow easy gopher passage.
Finally, in the alleys between rows of trees, you may wish to consider planting Melilotus indica, Sour Clover (or Sour Sweet Clover). This plant should be sown at 3 lb/acre. Gophers don’t like to eat this plant, reportedly due to its coumadin content (which all Melilotus spp. contain).
For certified organic production, the National List § 205.601 Synthetic substances allowed for use in organic crop production lists two materials for rodent control: sulfur dioxide smoke bombs (underground rodent control only) and Vitamin D3. These materials, while allowed, are likely not most effective means of gopher control, as gophers do not tend to feed on baits.
If used, bait should be part of an integrated pest management program. Per USDA’s National Organic Program (NOP) standards (see § 205.206 Crop pest, weed, and disease management practice standard), allowed pesticide materials should be used only when you have tried other methods and they are not sufficient. Nonetheless, any material should be included in the Organic System Plan that has been approved by your organic certifier. Natural materials, in general are allowed. However, a few, such as strychnine, are prohibited (see NOP §205.602(h)).
Synthetic materials are generally prohibited, with the exception of a few specific exceptions that are allowed and included on the National List. § 205.601 Synthetic substances allowed for use in organic crop production. (g) As rodenticides. (1) Sulfur dioxide — underground rodent control only (smoke bombs). (2) Vitamin D3.
Vitamin D3 cannot be the sole means of rodent control. Alternative methods for rodent control must be documented in the Organic System Plan. Growers must take precautions to prevent killing non-target animals.
There are some propane-powered devices that can be used to create an explosion in the gopher tunnel. While previously allowed, the use of these devices is no longer allowed for rodent control on organic farms. The method was discussed in 2002 in the CCOF magazine where its benefits were touted along with sound advice on precautions, However, the determination was made by the NOP at a January 2007 certifier training that this method is not allowed in organic production. This message has been communicated broadly by accredited organic certifiers (see the CCOF website regarding Propane for Rodent Control).
Please be aware that propane combustion has been identified as a rodent control material incompatible with organic production. Commonly, this is marketed as an injection and combustion system under the Rodenator brand. While CCOF previously approved this use, recent clarifications from the National Organic Program during the certifier training in Asilomar (Jan, 2007) have made it clear that organic growers may not use this or other similar products for rodent control in organic fields. Please note that CCOF expects the manufacturer to petition for inclusion of this use on the National List and CCOF may support the petition if requested by its clients. In the interim, CCOF will be requiring that certified growers immediately cease and desist use of all propane combustion based rodent control devices.
The reason for determining it to be prohibited is that propane is not the list of synthetic materials allowed for rodent control. Although CCOF petitioned the NOP in 2010 to allow its use, there has been no further change in status; it is considered not allowed for use on certified organic operations at this time.
Non-organic producers may still consider its use. I have heard from many producers, who have tried these devices, that they are very effective. However, not one of them was continuing to use it because they had gotten complaints from their neighbors. The sound of the explosion is quite loud — similar to a gunshot. You can see more information on the websites of companies that produce such devices:
Rodex: http://www.rodexindustries.com or 1-800-407-2943
Rodenator: http://www.rodenator.com or 1-800-750-4553
Gopher Control on Organic Farms. Thomas Wittman. The Cultivar Spring/Summer 2004. pages 13-16.
PVC Owlbox graphics: http://kaweahoaks.com/html/barn_owl_house.html
1) Organic Materials Review Institute (OMRI) www.OMRI.org Generic Materials List.
2) An Overview of Cholecalciferol Toxicosis, The American Board of Veterinary Toxicology (ABVT).
3) Colvin, B.A. Barn owls: Their secrets and habits. Illinois Audubon, No. 216 Spring. 1986
4) Birds and Nature. Bird House Tables.
5) How to Manage Pests: Pocket Gopher University of Calfornia Integrated Pest Management
6) MontGuide fact sheet #2000-09/Agriculture Guide to Pocket Gopher Control in Montana. James E. Knight, Extension Wildlife Specialist
7) Thomas Wittman. 2006. Workshop notes.
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