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Critter Control: Scratching Below the Surface

Destructive and troublesome, gophers are in a major problem in turf and ornamental landscapes. Herbivores, they eat a variety of plants, roots, fruits, vegetables, seeds and nuts. They dig extensive underground tunnel systems and push excess dirt to the surface, forming horseshoe shaped mounds. Rarely leaving their burrows, Gophers are anti-social and territorial with only one living in each tunnel system. They normally only come to the surface to feed, and will plug holes up when finished. Traps and poison baits can be used to deal with them, but are time-consuming and not always effective in severely infested areas. Burrow fumigation is a fast and effective extermination method, which entails a fumigant infiltrating an entire burrow system, killing the gopher within a few hours. It does not leave a great deal of pesticide residue and dissipates in around 24 hours. It is also said not to harm or contaminate surrounding plants Gophers can be controlled by setting rattraps over the tunnel entrances. However, they could bury the traps and tunnel around them. -- Photo Courtesy of webshots.

Whether you care for a golf course, school district, commercial property or cemetery, one of your biggest challenges is controlling landscape rodents.

Gophers, rats, mice, ground squirrels, opossum, skunks and raccoons can make even the best groundskeeper want to pull his hair out. There are a number of products and trapping equipment on the market as well as a few schools of thought on how to control nuisance wildlife.

Moles have holes much like that of gophers, but are almost always found near sidewalks or other hardscapes. Since moles feed on earthworms, centipedes, insect larvae, and other invertebrates, the use of insecticides to reduce insect larvae and related invertebrates may eliminate enough of the moles’ food supply, especially in sandy or light soils, so that they either starve to death or move elsewhere. -- Photo Courtesy of

Sometimes confused with gophers, moles are not rodents, but instead are insectivores. They consume large quantities of earthworms and other insects. Like gophers they spend their lives underground but, unlike gophers, they do not eat plants. They do not break the surface to feed and instead build shallow tunnels that run just under the surface of the soil. These appear as snake-like ridges in the lawn or garden with a characteristic crack running the along the top. It is common for these ridges to run along the edge of hardscape features.With pressurized exhaust rodent control, successful treatment of moles demands that laterals are probed and filled with carbon monoxide. -- Photo Courtesy of

For centuries, people have recognized that rodents such as rats and mice are not only a nuisance but also a public health problem. They damage structures and carry diseases that threaten health and quality of life, and they can cause injury and death. One of the main ways to help protect landscapes from these disease vectors is gathering information about infestations and about the causative conditions of infestation. Accurate recordkeeping by landscape superintendents provides the information needed to manage rodent pest problems.

Rodent surveys of exterior areas are the primary means for obtaining information on rodent infestations where environmental health deficiencies support rodent populations. Survey areas should include commercial and civic buildings; vacant lots and public areas.

In urban areas, the rodent species primarily targeted in surveys are the Norway rat (Rattus norvegicus), roof rat (Rattus rattus), and house mouse (Mus musculus). The term, commensal is often applied specifically to rodent pests of the landscape, which partake of human food. House mice and Norway rats are the chief commensal rodents.

Voles are a species of mouse commonly called meadow mice or field mice.They are slightly larger than house mice and usually live outside although they can get into attics and garages as well. They often take over abandoned gopher tunnels. If you have little open holes in your landscaping or lawn, it is probably a vole problem. Voles live in large family groups and tend to repopulate problem areas very quickly if not dealt with aggressively. Though multi acreage treatment has not been done, individual colony treatment of voles has proven successful with pressurized exhaust rodent control.-- Photo Courtesy of

One of the principles of IPM is that it is preferable to take preventive measures against the arrival of commensal rodents and other pests, rather than having to fumigate commensal pests or otherwise exterminate them later.

Rodent surveys fulfill an essential surveillance requirement for every integrated pest management (IPM) program-the need for detailed information about conditions in a defined community.

IPM and Rodents

IPM is a long-term, effective, and holistic approach to managing pests of all kinds by carefully combining various interventions (e.g., education, code enforcement, rodent proofing, poisoning) in ways that minimize environmental hazards and deficiencies that affect people's health.

IPM requires a shift from the typical pest control efforts that often emphasize poisoning and trapping. With IPM, pests and disease vectors are managed by managing the environment. For IPM to succeed, the behavior and ecology of the target pest, the environment in which the pest is active, and the periodic changes that occur in the environment (including the people who share the environment) must be taken into account. In addition, the safety of the people, the environment, and the non-target animals such as pets and birds must be considered. An understanding of population dynamics is important because any successful strategy for the management of rodent populations depends on that understanding and on conducting appropriate interventions based on IPM principles.

Program and political support are essential in obtaining the necessary resources for an IPM program that takes into account the complex interplay of rodents, people, and environmental factors. The overall goals of IPM are to reduce or eliminate human encounters with pests and disease vectors and to reduce pesticide exposure.

Meyers Industries R2 easily eliminates rodents from pastureland, golf courses, levees, cropland, vineyard, and orchards with a simple push of the button, leaving no chemicals in the ground or in the animal's body. Additionally, the Rodenator R2 special design has a flexible hose head to increase tunnel pressure without overfilling the tunnel with gas while delivering a precision underground shockwave to the targeted animals’ tunnels and dens. Not only does the Rodenator Pro exterminate the critters, but also can collapse their tunnel systems to prevent re-infestation. -- Photo Courtesy of rodenator

Program Components

The four key components of an IPM program are survey, tolerance limit, intervention, and evaluation. If a key component is omitted, success in managing or eliminating pests is reduced.

Surveys (inspection and monitoring):

Survey results determine the need for a rodent IPM program and the direction the program must take to manage the rodent problem. A rodent survey has four distinct phases:

  1. Premises inspection (comprehensive or sample) of defined areas (e.g., groups of blocks) to record infestations and their causative conditions;
  2. Preparation of maps, graphs, and tables to summarize survey results (may include photographs of field observations);
  3. Preparation of a report that includes an analysis of block and premises data, and premises prevalence rates for infestation and its causative conditions;
  4. Recommendations to resolve the rodent infestation problem.

Tolerance limit (action threshold):

The level at which a pest causes sufficient damage to warrant public health attention and intervention. Real or perceived damage can be aesthetic and can have economic, psychological, and medical consequences. In 1972, CDC established tolerance limits for rodent infestation, exposed garbage, and improperly stored refuse. The survey establishes the baseline on rodent infestation and on the causative conditions that support the infestation. The goal is to reduce both the infestation and the causative conditions to a level at which they no longer have an adverse effect on the community.

Not only can opossums wreak havoc on your turf and sod, the rat-tailed mammals may hit closer to home by causing damage to buildings on your landscape as they try to gain entry. Opossums are North America's only marsupial, which means opossum babies live in mother's pouch. White or gray with long, pointed faces, and bodies about the size of a house cat, Opossums' 50 teeth number more than any other North American mammal, and their canine fangs are very visible. They will raid garbage cans in search of food, and in cities a chimney, attic, wall void and crawlspace may serve as a comfy substitute for a hollow tree as an opossum den site. A homeowner may successfully trap and kill an adult opossum, only to smell the nasty odor of five opossum baby carcasses rotting in the wall. -- Photo Courtesy of


Actions taken to prevent, reduce, or eliminate rodent infestations and their destructive effects. Survey data determine when, where, what, and whether interventions are necessary to prevent or eliminate a particular pest problem.

Interventions are classified as educational, legal or regulatory, habitat modification, horticultural, biologic, mechanical, and chemical. These intervention categories typically form an IPM strategy. Most commensal rodent IPM programs emphasize educational and legal or regulatory interventions, and habitat modification.

The key to a successful IPM program is the elimination of the causes of infestation (i.e., food, water, and harborage). The judicious and careful use of pesticides (including toxicants) to manage pests is also important for success.

A vital IPM "rule" for selecting rodenticides or other pesticides is that the product chosen should be the least toxic product that will be effective on a target pest. The product also must have a highly efficacious and readily available antidote that can be administered in a timely manner for both humans and pets if a rodenticide is inadvertently ingested. Widespread and indiscriminate use of pesticides has serious consequences for people, animals, and the environment.

Ground squirrels strip flower beds and excavate large burrows. They undermine banks and slopes and, when numerous enough, will move right into flat turf areas. Squirrel populations can soar dramatically when the young emerge from the burrow in spring. Litters containing as many as 14 offspring are common. Ground squirrels are most apt to move into new territory after a good rain because it is easy to dig a new burrow and also in late spring when the population soars due to the breeding cycle. Using chemicals and repellants may get them out but you must keep applying more. Using traps is best left to an expert trapper. -- Photo Courtesy of


The evaluation process (composed of periodic surveys) determines whether IPM interventions have been effective or whether they need to be repeated or modified. The initial survey of residential and commercial blocks and the periodic resurveys (monitoring) of a target community provides the basis for the evaluation of a program's progress.

A rodent survey is an essential tool in the IPM effort to manage rodent problems

To determine the magnitude of the rodent problem, determine priorities, and evaluate progress, the IPM program must maintain a premises and block records management system. The system should provide for sequentially reporting survey findings using standardized reporting forms. The rodent survey involves an exterior inspection of premises to record significant data such as active rodent signs, rodent entries to buildings, and environmental deficiencies that provide food, water, and harborage. Although the Norway rat and the roof rat generally live outdoors, they do enter buildings that are not rodent proofed. The house mouse can survive outdoors, but it prefers indoor areas in an urban habitat.

A rodent survey is an essential tool in the IPM effort to manage rodent problems. The survey provides precise information about infestations and their causative conditions, and it measures progress toward their elimination.

Valid surveys should be made to determine the magnitude of infestation problems and their causes, for implementing interventions, and for measuring progress.

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October 13, 2019, 6:46 pm PDT

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