DESPERATE MEASURES Using poison to control gopher populations puts their natural predators at risk
Putting out poison bait for gophers should only be done in extreme situations and as a last resort.
Raptors, coyotes, weasels, badgers and foxes are often killed by scavenging on poisoned gophers, and reducing the number of natural gopher predators only prolongs the pest problem in the long term.
However, if poison is the only option, producers have several poisons to choose from. Ready-to-use (RTU) strychnine baits are available commercially, as are several other toxicants such as Rozol on wheat, concentrated liquid Rozol and zinc phosphide (BOBS) bait on oat groats
Timing is important. If done by May, more of the mothers will be killed and with them, either their unborn offspring or those too young to care for themselves. However, once the young emerge to forage above ground, keeping on top of the population becomes much more difficult.
Pick your poison
A comprehensive field study by Dr. Gilbert Proulx in 2007 comparing the effectiveness of Rozol, Phostoxin and strychnine concluded Rozol was most effective, but only if used before green-up. However, Rozol requires multiple baitings, which actually puts non-target species even more at risk.
“We were hoping that the Phostoxin panned out better than it did,” said Phil Merrill, an inspector with Alberta Agriculture.
“We were hoping that Rozol did better than it did. Rozol will effectively kill at a high enough rate that we can say it’s a good control before green-up, but after green-up it doesn’t kill the 70 per cent that it requires for population reduction. If you’re not killing 70 per cent of the gophers in your control program then you’re not knocking down the population enough to make an effect for next year.”
Rozol takes a few days to kill the gopher, with the poisoned animal becoming sick and sluggish, making it an easy meal. Unfortunately, there’s no such thing as a free lunch, and raptors such as hawks will pay for the mistake with their life as well.
Zinc phosphide and Phostoxin are both non-selective and will kill everything down the gopher hole, including snakes, weasels and mice. Phostoxin can only be administered by someone with a pesticide applicators licence.
Strychnine is often the weapon of choice to wage chemical warfare against gophers and RTU strychnine baits are available at ag supply stores. However, in cases of severe infestation, Liquid Strychnine Concentrate (LSC) can be purchased from an Alberta Agriculture Service Board, but only with the approval of the local field man. The LSC must be mixed and diluted to the same rate 0.4 per cent ration as RTU baits.
Some studies have shown freshly prepared baits are more effective, which is why it is made available for severe infestations. However, it’s also more dangerous for the environment as people may make the baits stronger, either because of human error or because they believe they will kill more gophers that way.
“We’re not sure if it’s because it’s fresher, or wetter,” said Merrill. “I’m almost wondering if it isn’t because of the dampness in the bait. They don’t like the dry powder and you put out a damp bait and the gophers just eat it better.”
Bring out your dead
Producers must adhere to strict conditions in order to use liquid strychnine, such as baiting below ground, and having water available while mixing in case of spills or accidents. Strychnine cannot be used if there is a species at risk on the property, and the treated gopher holes must be filled in.
One of the most important conditions is to pick up and dispose of the dead to prevent scavenging and thus the poisoning of non-target animals. Producers are required to monitor the treated area for carcasses every day for one week after baiting, and once a week for the following two weeks.
“It doesn’t take long — it’s not something you have to wait until evening to do. You put it out and you can come back within three hours and you’ll probably pick up most of the dead,” said Merrill.
Strychnine kills gophers within minutes, often after consuming just a few kernels. It is a neurotoxin, and it excites the entire nervous system causing convulsions throughout the body. The cause of death is typically asphyxiation as the result of paralysis of the respiratory muscles.
Many states and countries prohibit its use in any form because of the devastating effect it can have on wildlife. Domestic livestock and even people are sometimes accidentally poisoned during the mixing process. Victims will often die before they reach the hospital.
“It’s effective, but it kills other things as well is the problem,” said Merrill.
LSC had been banned in Canada because of the possible effect on non-target species, but it was reapproved in 2007 after pressure from the agricultural sectors in Saskatchewan and Alberta.