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Pest control.

The last two months have been spent discussing gophers in general and biological control specifically. This month I will wrap up the gopher subject with a somewhat detailed look at the two most effective methods of gopher control available, chemical control and trapping.

It is important to remember that gophers spend almost their entire life below ground. The only exception is a brief period during their breeding season when gophers travel above ground to find a mate. Juvenile gophers are kicked out of the den by their mother, and will travel above ground until finding a suitable location to begin burrowing.

Gophers also are opportunistic and will inhabit an existing burrow system that is vacant. This needs to be considered when reviewing an area of successful treatment, since gophers will reappear eventually.

There are three types of chemicals used for gopher control. I want to discuss all three as well as fumigants. The first is strychnine, which is an acute toxicant, meaning one feeding is required by Mr. Gopher to achieve the desired result. Strychnine is available on milo or rolled oats and in three concentration formulas: .35%, .50% and 1.8%. Strychnine is a Category I rodenticide; the .50% and 1.8% formulas are restricted to use by individuals carrying a valid Qualified Applicators License (QAL). The advantage in using an acute toxicant is that you achieve quick results, since a single feeding is all that is required; therefore, the chance of bait shyness is minimized.

Chlorophacinone and diphacinone are chronic toxicants, meaning multiple feedings are required to achieve mortality. Available in .005% concentrations on milo and rolled oats, this is the most commonly used rodenticide.

A fourth chemical, aluminum phosphide, is available as a restricted-use material that may be applied only by licensed and qualified technicians. This chemical is extremely effective as it produces a gas when it interacts with the humidity in a burrow system.

The use of this product requires special qualifications to transport and apply. If you are interested in trying this fumigant, contact your local supplier for the current requirements to transport aluminum phosphide.

Using the small end on the probe, begin pushing into the soil about 12 to 15 inches behind a mound. The tunnel is detected by a brief end to resistance on the probe. The large end of the probe is then used to open a hole to accommodate a funnel which is used to insert bait into the burrow. Probing for tunnels can be challenging. If the soil is dry, rocky, or extremely wet, the dropping sensation felt when the probe goes into a tunnel may be masked. Work slowly, and with practice you'll get it.

Now that you've located the runway and opened a hole, it's time to insert the funnel and measure the correct amount of bait into the funnel. This is where reading your label instructions prior to application comes into play. I cannot emphasize how important it is to follow the label instructions. Not only does it control effectiveness it controls the amount of money spent on bait. More bait does not mean more killing power - in fact it can be just the opposite. If the bait does not directly funnel into the burrow, use the small end of the probe to push it in. You should always wear gloves and safety equipment when handling rodenticides. If you are unclear what equipment may be required read the label. The funnel should be carefully withdrawn to avoid spilling bait above ground. Milo and rolled grain baits will mildew and become unattractive to gophers if baiting is done just prior to or during a ram storm. For this reason gopher baiting is most effective when the soil is dry and the bait has a chance to last the longest.

The opening left by the probe should always be resealed. Gophers are extremely sensitive to pressure changes and air flow in their burrow system. An opening with bait left unsealed will be sealed when the gopher backfills that area of the tunnel and covers the bait with dirt. At least two "sets" (for this article a "set" refers to the probing, baiting and sealing process) should be made per gopher system to be sure that the bait is found. When using chlorophacinone and diphacinone, up to four sets may be required, two to four times a week, to do the job.

Before moving to the next treatment site all soil mounds should be kicked down. This allows you to monitor the effectiveness of your treatments. It will also allow you to see areas of reinfestation when they occur. I say this because it will happen and you need to be prepared for it. Unfortunately, gophers don't ignore an area once you've cleaned it out with baiting and trapping; they will eventually return, but in manageable numbers.

When trapping, the same probing technique is used for locating the runway. Once it's been located, the next step is to cut a 16[inches] diameter plug with a round point shovel, using the probe hole as a center. Find both tunnel sides (look again at the diagram) and clear with a small, hand-held garden trowel. You are now ready to insert the traps. As we discussed in an earlier column, there are three or four widely accessible and effective traps for gophers. All do basically the same thing, having a trigger pan or bar that is tripped when a gopher runs into it releasing a spring-loaded arm that stuns and traps the gopher. What makes these traps effective is that they quickly incapacitate and kill the gopher. When you place the trap, it is important that you anchor it above ground, or to the other trap in the runway. When you replace the dirt plug it will anchor the traps for you. You will also want to mark the trap locations, using flagging or marking paint so they are easy to find and check every 24 to 48 hours.

The third method for gopher control is the use of gas cartridges, commonly called "smoke bombs." Gas cartridges are lit and then inserted into the runway system. The system is then quickly sealed and the smoke travels throughout the tunnels and replaces the available oxygen. This can be an effective technique when you have soft, moist soil conditions, usually in the spring or late fall.

The use of fumigants and trapping should not be viewed as a replacement to chemical control. Best results for gopher control will be obtained using chemical control products. Trapping and fumigants should be used to supplement a chemical control program. Bait-shy or hard-to-get gophers can be cleaned up nicely using a trap. Because trapping is so labor intensive, it doesn't make good economic sense to rely on it for your only method of control.

The best approach to gopher control is to integrate the techniques and practices we've discussed in the last three articles. Next month we're going to switch gears and talk about birds and netting. Is netting really worth the "hassle"? We'll see.
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Title Annotation:wineries
Author:Taber, Mike
Publication:Wines & Vines
Date:Apr 1, 1996
Previous Article:Napa Ridge: the value of efficiency.
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