Anything we can find out now can be used by regulators to make more informed decisions.” Letourneau takes nothing for granted as the research gets under way. The project will use a large number of sample plants on varied research sites, and the experiments will be replicated over three years. Hazards of GM corn, including allergenicity and contamination of adjacent fields, were identified during extensive testing that was required because it is a food. Because similar tests are not required on nonfood plants, it’s harder to know what the hazards might be, and what the probability is that they’ll occur, said Letourneau. “It might be that transgene movement to wild relatives would be no problem at all,” she said. “If we don’t detect any problems or hazards, we’ll feel we’ve tried to provide the data needed for risk assessment.” The three-year project is funded by a $335,000 grant from the U.S. Department of Agriculture.Some cover crops can both benefit your crop rotation or winter fallow and help limit gopher populations. Research has shown that gophers much prefer clover cover crops over small grains such as barley,hydroponic nft channel oats and Sudan grass. And although most clovers attract gophers there is a sour clover that appears to discourage them.
This can be used as a winter cover combined with a small grain to move populations out of the fields to areas where they can be trapped. I’ve also observed that gopher populations move to farm road edges and other border areas when a winter cover crop of bell beans or fava beans are planted. Be aware, though, that many studies have shown gophers to be extremely adaptable in their feeding habits, so no cover crop will guarantee a gopher-free field. When considering rotations on diverse farms, include gophers in the equation. If you follow a crop that attracts gophers, such as potatoes, with another that they feed on, like onions, you will exacerbate gopher problems by providing a continual food source. However, if you follow potatoes with a sour clover or small grain, populations are less likely to rise. Farmers and gardeners have tried all manner of barriers to discourage gophers. These include wire mesh, gravel, trenches filled with glass and rocks, corrugated roofing, even trenches with buried buckets that act as pitfall traps—anything that presents an obstacle for persistent gophers. These all have some effect on slowing invasions. The most promising approaches are those that create both an above- and below-ground barrier.
One of the most successful is fencing made of steel corrugated roofing. Not only is it impenetrable, but gophers cannot climb the exposed portion. Because gophers can scale a welded wire fence, above-ground wire barriers must have the wire bent outward at the top or a wooden or metal rim installed. I’m currently experimenting with a material called “Root Guard,” a thirty-six inch wide plastic sheeting seventy mils thick used by landscapers to keep bamboo roots from spreading. At $3–$4/foot, Root Guard is too expensive to use in large-scale operations, but may be cost effective for areas of an acre or less. Large farms may benefit by blocking major gopher access routes with any available solid material, but I don’t believe there is a viable material that will completely head off an infestation.Although not appropriate for all operations, flood irrigation can be extremely effective not only at killing gophers under the water but also at driving the survivors to field edges where they can be trapped. Flooding burrows with a hose can sometimes be effective in a small operation, providing that it is done at a fresh burrow. Gas cartridges with sulfur and sodium nitrate as active ingredients are still allowed by organic certifiers and can be effective if used on new burrows . They cost $1–$2 per cartridge and have an approximately fifty percent success rate. After inserting a gas cartridge in a burrow, be sure to cover the opening to prevent the gas from escaping.
One company sells a blower that is supposed to move the gas beyond blocks in the tunnel system. I feel this may dilute the strength of the gas, although no scientific evidence yet exists to validate this idea. The “Rodenator Pro” is a device that injects a mixture of propane gas and oxygen into a gopher burrow and then ignites it with a spark, destroying the tunnel system. I recommend occasional use of the Rodenator in vineyards and orchards to remove permanent tunnels that run along perennial crop rows. It’s not appropriate for annual vegetable operations as it can damage crops and is unwieldy in row crop settings. Some growers use trapping as a main strategy and the Rodenator for areas where gophers and ground squirrels have settled. A truck or tractor is needed to move the propane and oxygen tanks around the site to be treated. Barn owls are the most effective gopher predators—their diets can consist of up to ninety percent gophers, and a barn owl family attracted by a nest box can eat up to a thousand gophers per year. There are many designs for barn owl nest boxes . The main criteria is that the box’s opening be approximately five inches in diameter; any larger and the barn owl’s main predator, the great horned owl, can get at the young birds Gopher snakes do in fact eat gophers, but only one every six weeks to two months. Bobcats and coyotes also eat gophers, although I’ve found that coyotes prefer gophers caught in traps, which often disappear after they dine. Domestic cats can be a significant help in controlling gophers. Cats hunt more when well fed and cared for, as the sporting aspect seems to be the attraction. After poison baits, which are no longer allowed under organic certification rules, trapping is the most effective way to control gophers.
The best sites for setting traps are where there has been recent activity, marked by fresh mounds of moist, dark soil in the morning or by holes that have been recently plugged. Three trap designs currently dominate the market. The most common in California is the Macabee trap, invented by Zephyr Macabee in 1900 to protect his Santa Clara Valley almond orchards. The Macabee is a “pincher” type trap that impales two wires in the body of the gopher when it bumps into a trigger. The usual set for these traps is to locate and dig down to the main, larger burrow and insert two traps facing away from each other, connected by a wire. After the set is completely buried the wire is left on the surface and flagged to help find the traps. There are different opinions about letting light and air into the tunnel where the trap is located. Some say light and air will encourage the gopher to pack the trap area with soil and not set the trap off,nft growing system and some say it is the light that draws the gopher to the trap. I’ve found that both methods work and that adding some vegetative bait helps as well. I’ve seen some modifications where the Macabee trap is inserted into a section of two-inch ABS drain pipe about eight inches long, either left open or closed at one end . This addition seems to help catch the gopher even if it is pushing soil ahead of it. Another older, standard trap design that is still popular is the box trap. This small wooden box is open on the bottom and at one end, and houses a trigger and metal “choker” loop or cable that grabs the gopher as it enters. A more modern version called the “Black Hole” is made of plastic tubing and a cable choker. These traps work by fooling the gopher into thinking it is still in the tunnel. The gopher is lured to the end of the trap where a small opening allows light and air in and the gopher gets caught trying to close the opening. Box traps are also placed in the main tunnel in pairs, although I’ve seen a single trap work when placed in the mound’s entrance tunnel. Although both Macabee and box-type traps are effective, I’ve had the most success using the Cinch trap from Oregon. This is also an older trap that for many years was used only by professionals and can be slightly hazardous and difficult to set due to its double trigger and strong spring. It was originally designed for moles but is extremely effective on gophers. Like the box or Macabee traps, Cinch traps can be used in pairs, but can be set more quickly and can be even more effective than the other trap types when placed singly in the burrow entrance. The method I use is to open the burrow at the freshest mound and insert the round, extended jaws of the trap into the burrow entrance. I use a stake that is sized to open the burrow as wide as the trap’s jaws and then use the same stake to mark the trapping site.
The gopher is caught when it comes to the surface to close the opening in the mound. Interestingly, the unvacuumed trap crop treatment did not show a significant difference in damage when compared to the vacuumed trap crop in June, even though it accumulated more WTPB in rows 1–8. Also interesting is the fact that the highest damage was seen in the untreated control, which did not accumulate high numbers of WTPB. This could indicate that WTPB not associated with or feeding on nearby trap crops do more per capita damage to strawberries. “It’s possible that trap crops may partially satiate WTPB and thus minimize the amount they feed on developing berries, so that WTPB abundance alone does not correspond well with strawberry damage estimates,” says Swezey. “This is a hypothesis we plan to pursue in future research.” In July, vacuuming the alfalfa trap crop reduced WTPB numbers by 79% compared to the unvacuumed trap crop . Except in row 1, the vacuumed trap crop treatment also had the same accumulated number of WTPB as either the whole-field vacuuming treatment or the untreated control. Vacuuming the trap crop reduced total damage to the strawberries in July by 49% when compared to the unvacuumed trap crop , although no significant differences could be detected between the vacuumed trap crop and either the whole field vacuuming or untreated control treatments. These results show that in July, WTPB in an unvacuumed trap crop will generate significantly higher damage to adjacent strawberry crops than other treatments. “We do not want the trap crop to become a source of pests,” says Swezey. “That’s why it’s critical to manage it throughout the growing season.” The research team is still evaluating data collected in August 2003 to see whether the differences in treatment continued through the late season. The big-eyed bug , Geocoris spp., was the most abundant beneficial insect collected from the trap crop and strawberry fields. This native insect feeds on WTPB eggs and nymphs. Results from the 2002 study show that in June, the vacuumed trap crop treatment had significantly more BEB in the trap crop and all strawberry rows than did the other three treatments. This result indicates that the trap crop vegetation increased the numbers of the most abundant generalist WTPB predator in the strawberry rows at the farthest distance sampled. This effect was somewhat less prevalent in July, and by August BEB populations had declined in all the treatments, possibly as a result of the BEB entering diapause.Results from 2003 are still being analyzed.Results from this study show that a field edge alfalfa trap crop can successfully attract and concentrate WTPB numbers, and that tractor-mounted vacuum devices can remove significant numbers of WTPB from the trap crop. The trap crop vacuuming treatment offers the same or reduced WTPB damage to fruit in adjacent strawberry rows when compared with the grower’s whole field vacuuming program. “The study also showed us that, at least for WTPB, alfalfa is a terrific trap crop,” says Swezey. “We wanted to develop a type of vegetation management system specific to this pest, and I think we’ve shown that alfalfa is effective.” Swezey also cautions that trap crops must be used carefully. “It’s one of those ‘Don’t try this at home’ situations,” he says. “If you’re going to use trap crops, you have to be ready to manage them as diligently as the crop itself—that includes irrigation, fertilizer, and weeding—and then you have to manage the pest once it’s in the trap crop.” Perhaps the most important result for the Pacific Gold growers was that vacuuming the field-edge trap crop reduced the operation time of their tractor-mounted vacuum by 75% as compared to vacuuming the entire strawberry field, while giving the same or better level of WTPB control. This approach to limiting WTPB damage translates to savings in operator time, tractor wear, and fuel costs.