As reported in High Plains Journal Gary Witmer, Ph.D, a retired Colorado federal research biologist who specialized in rodent damage and management, said rodents comprise the largest taxonomic group of mammals with more than 2,200 species occurring in the world. They occur on all continents with the exception of Antarctica. Most native species of rodents do not cause significant damage where they occur, but there are a handful of exceptions on each continent.
Kansas State Agricultural College, now known as Kansas State University, through its Agricultural Experiment Station’s Department of Zoology, had issued a lengthy bulletin on how to control mammals that are distinguished by the presence of two long curved chisel-like teeth in the front of each jaw. The bulletin was issued in 1925 and the paper dealt with the suppression of harmful rodents that included the pocket gopher, prairie dog and rat. It also dealt with the mole, which is an insect-eating animal and is not a rodent.
Drew Ricketts, an Extension wildlife specialist with horticulture and natural resources at K-State, said in rangeland and forage systems, the challenge is predominantly prairie dogs and pocket gophers. Moles, ground squirrels and mice can also cause headaches for farmers and ranchers where row crops are grown and harvested.
Prairie dogs and pocket gophers crave certain habitats.
“The big challenges for both species is they spend a lot of time below ground,” Ricketts said. “We can put up fences for some critters to keep them out but that doesn’t work in their case.”
Witmer said the species that cause damage to farming and ranching operations varies somewhat by geographic location. However, some of the most damaging in North America are ground squirrels, prairie dogs, pocket gophers and moles. And, of course, invasive rats and mice cause lots of damage in and around all agricultural buildings.
“Native rodents are adapted to the native habitats that they occur in,” Witmer said. “Most require food, cover and a safe place to nest and raise their young. Most require free-standing water to drink, with the exception of pocket gophers and some arid land species, which get their water requirements out of the vegetation they eat.”
In crop fields and pastures, rodents cause the most damage by clipping, gnawing and feeding on plants above ground, Witmer said. However, some rodents, especially pocket gophers, do extensive damage below on root systems because they spend most of their time below burrowing below the surface.
“Rodents, especially rats and mice, cause extensive damage to stored grains and livestock feeds. This is not only by feeding on it, but also by contaminating it with their urine and droppings,” Witmer said.
Ricketts said prairie dogs and pocket gophers can adapt to different soil textures. Pocket gophers have more latitude while prairie dogs will select a loamy -type of soil.
The pocket gopher needs to have soil that is not too sandy because that prevents a burrowing system. and It also does not like high clay content that because italso prevents them from digging and burrowing, he said. Both rodents need a decent soil profile to maintain their burrow system.
“Vegetation hinders prairie dogs to expand their colonies, which is why they more often flourish in the western rangelands than the tall grass prairies in the eastern prairie,” the K-State specialist said.
Land use makes a difference
Land use in and around agricultural land can make a big difference to rodent populations, Witmer said.
Conservation lands and even the vegetation along roadways and utility easements provide cover and food to rodents, he said. This provides refuge for rodents after crops are harvested. Once crops begin to grow again, the rodents can reinvade those crop areas.
Arid and semi-arid lands often limit rodent populations because of their conditions. “Unfortunately, our agricultural practices often improve conditions for rodents,” Witmer said. “Irrigated crops are a good example, providing good food, cover and moisture for rodents. Growing nutritious crops, such as legumes, are another example.”
Acreage enrolled in the Conservation Reserve Program also can change habitat for rodents, Ricketts said. CRP acres are typically planted to tall grass species. Once those grasses get tall it makes it difficult habitat for prairie dogs, he said. Pocket gophers are impacted by annual soil disturbance. In western rangeland areas that scenario could provide habitat particularly if cropland had been converted to CRP.
Alfalfa field, pasture damage
Pocket gophers can be devastating in alfalfa fields, Ricketts said. “You can see 20 to 50% reduction in forage production when pocket gophers are in a high infestation.”
Using a crop rotation like wheat, corn or another annual crop that could breaking a long period of alfalfa production is one strategy that could also make economical sense for the producer.
Meanwhile, Ricketts said prairie dogs can have a direct impact, too.
The prairie dog in pasture with 60% occupancy, based on one study from Colorado, has shown an 8% reduction in average daily gain of steers in an average precipitation year.
“When we have drought the prairie dogs can really devastate vegetation. Rehabilitating that pasture, even once the prairie dogs have been eradicated, can really take a lot of time because they select the same species of grass as the cattle do.”
Control their habitat
Producers should consider a plan to try to make the lands bordering ag fields less supportive of rodents, Witmer said. This may involve mowing or burning, or planting plant species that are not desirable to rodents, such as endophytic grasses, which contain a fungus that makes them unpalatableless palatable.
“After harvesting crops, we sometimes leave substantial plant residues for purposes of reducing erosion and holding moisture. However, this also provides cover and some food for rodents during ‘hard times’ such as winter,” he said.
Survey
It’s a good idea to survey for rodents, although that takes some time and effort, Witmer said. One way to do this is to put out a grid of 10-by-10 meters or yards. At each station look for signs of rodents (tracks, digging, droppings and plant gnawing). Record the number of stations with rodent sign. If 10 or more of 100 stations show a sign of rodents, it is often suggested that some rodent control be started, but this is not a fast rule, he said. More careful and informative rodent monitoring involves the use of traps or chew blocks at the stations.
Additional action
If a farmers or rancher decides to undertake rodent control beyond the habitat management methods, he can implement direct rodent control using traps or toxicants, Witmer said. “It’s important to check with regulatory agencies to see what is recommended and legal in your area. And, of course, these methods are more expensive and labor intensive.”
Ricketts said if the infestation reaches a high enough count for either prairie dogs or pocket gophers and losses are significant the farmer and rancher may have to use toxicants. For lower levels of infestations, particularly for pocket gophers, then trapping can be effective. It can be time- consuming and the best results are for acreages of 50 acres or less. From a practical standpoint if the infestation is high and the fields are larger than toxicants is the most effective eradication tool.
The toxicants are not cheap and they are considered restricted use pesticides, he said, and most likely a producer will need to work with a licensed applicator. A producer can get a private applicator’s license as long as he follows all the regulatory requirements.
Substantial damage can occur if rodent populations build up beyond a “background” level, Witmer said. This can happen if land practices make things better for for rodents. A mild winter can also cause somewhat of an outbreak as can a series period of higher-than-usual precipitation. Planting—-or avoiding planting—-certain types of vegetation can help serve as a deterrent too.
Constant watch
Rodent damage can be more severe when conditions are poor for them, Witmer said. During drought or poor food and water conditions, they will try to do whatever it takes to survive. Their mortality rates will be high during these times, and reproduction many be poor, but crop damage can still be high for a while.
Not only do rodents consume and damage crops and pastures, but they also pose a health hazard to people and animals because of the diseases they can carry and pass on; these include plague, hantavirus, leptospirosis and many others.
