- Author: Belinda Messenger-Sikes
During the holiday season, the only creatures you want stirring in your home are your family, friends, and pets. But as temperatures drop, and the rain returns, some pests may seek shelter indoors with you. Rats and mice can be problems all year but in the cold weather, they prefer the warmth of your home to being outdoors and you might see more in your home.
Pests invade homes for varying reasons during autumn and winter. Common outdoor species such as Argentine ants, Oriental (or Turkestan) cockroaches, sowbugs and pillbugs, springtails, and earwigs, may simply be escaping harsh conditions such as freezing temperatures or small-scale flooding. Some insects, especially true bugs (Hemiptera); such as boxelder bug, bordered plant bug, milkweed bug and other seed bugs, false chinch bug, and various stink bugs, naturally seek out dry, protected cracks and crevices to spend the winter. In the landscape, such sites may be beneath loose tree bark or deep within firewood piles, but structural gaps, cracks and crevices may be warmer, drier, and more attractive to these overwintering bugs.
It's generally easier to keep pests out before they become a problem than to try and get rid of them once they infest your home. Exclude pests by sealing up possible entry points around doors, windows, foundations, chimneys, roof joints, shingles, and vents. Install door sweeps and threshold seals to get rid of gaps under and around doors. If you have gaps around windows, you can close them with weather stripping and expanding foam or install new screens.
Clean up the landscape around your home so pests have fewer places to live and breed. Move wood chips and other organic mulches, and firewood piles away from your home's perimeter and entryways. Drain any excess moisture near structural foundations and entryways.
If you spot nuisance pests like boxelder bugs, earwigs, springtails, and centipedes indoors, they can be simply swept up, vacuumed, or taken outside. Other pests like mice and rats need to be dealt with differently.
Ideally, mice and rats should be managed before they get inside. Check the exterior of your home for signs of a mice or rat infestation including droppings, gnaw marks, feeding damage, and rub marks. For mice and rats, tight fitting lids on garbage cans and compost containers will keep these rodents from finding a food source near your home and eventually coming indoors. Thin vegetation between shrubs and buildings and trim back overhanging trees. Roof rats will use climbing vegetation to scale buildings and seek shelter. Seal any cracks or gaps into your home that are larger than 1/4 inch. Screen or block potential entrances under eaves or overlapping roof sections. Use sheet metal or 1/8-inch wire hardware cloth to keep out mice and rats since rodents can gnaw through softer material like plastic or wood.
Snap traps are the safest, most effective, and most economical way to manage rats and mice. You can place traps outside the home to catch rodents before they enter. You can also place them inside if you spot signs of them there. Be sure to use the correct-sized traps and place them in secluded areas along walls, behind objects, in dark corners, and in places where droppings have been found.
Keep pests from ruining your holiday fun by denying them food, water, and shelter in your home. For more details about specific pests and their management, see the UC IPM website https://ipm.ucanr.edu/PMG/menu.homegarden.html.
[Originally featured in the Winter 2023-2024 edition of the Home & Garden Pest Newsletter.]
- Author: Lauren Fordyce
Most people don't think about rats or mice until they become pests in or around the home. But with experts predicting that these pests will be particularly bad this upcoming winter, you might want to spend some more time rodent-proofing your home and other buildings.
A new report from the National Pest Management Association (NPMA) predicts an increase in rodent infestations from the cool, wet weather we've had in California. When temperatures drop outdoors, rodents often seek shelter in buildings to keep warm. They can enter through small cracks in foundations, screens, or trim. Once inside, they can damage the structure, destroy food, and transmit diseases to humans and other animals.
Some general tips for keeping rats and mice out include:
- Check around foundations, roofs, water pipes, vents, and utility cables for openings. Seal exterior cracks and holes larger than ¼ inch with wire mesh, steel wool, sheet metal or concrete. Rodents can chew through caulk, expanding foam, plastic, wood, and other soft materials.
- Make sure all exterior doors and windows fit tightly.
- Keep food storage and garbage containers sealed. Store pet food in rodent-proof containers and avoid leaving excess pet food out.
- Clean up crumbs or spilled food immediately.
- Remove or thin vegetation around buildings. Roof rats will use climbing vegetation to scale buildings and seek shelter.
If you have rodents indoors, the best way to control them is with snap traps. Dispose of dead rodents by placing them in plastic bags and putting them in the garbage. Do not touch rodents with your bare hands.
Learn more about managing rodents in the UC IPM publications Pest Notes: House Mouse and Pest Notes: Rats. If your rodent infestation is too much for you to handle on your own, consider Hiring a Pest Control Company.
- Author: Lauren Fordyce
You may not think about rodents such as rats, mice, or gophers until they become a pest around your home. Because rodents can be major pests in and around homes, gardens, landscapes, restaurants, and other buildings, each year pest control experts “celebrate” Rodent Awareness Week. Rodent Awareness Week (October 16-22) is an annual campaign created by the National Pest Management Association to educate the public about the potential harm associated with rats and mice. In addition to damaging structures and property, rodents can transmit diseases to humans and other animals. During the fall and winter months, rodents will seek food and shelter in homes and other buildings
Some general tips for keeping rodent pests out, include:
- Seal structural cracks and openings larger than 1/4 inch. Utilize weather stripping or door sweeps, and ensure doors and windows fit tightly. Wire screen can also be used.
- Keep food storage and garbage containers sealed.
- Remove or thin vegetation around structures. Rodents, especially house mice, will use climbing vegetation to scale buildings.
- Don't touch rodents with your bare hands. Dispose of dead rodents by placing them in plastic bags and putting them in the garbage.
- Avoid poison baits as the rodents can die in hidden places and they can be harmful to children and wildlife.
House Mice
Adult house mice can be 5 to 7 inches long with 3- to 4-inch-long tails. They are light brown to gray rodents with a characteristic musky odor. House mice are well adapted to living in close contact with humans. They are most active at night, but you can also see them during the day. Check behind boxes, in drawers, or around woodpiles for nests made of finely shredded materials. Control them by placing snap traps or glue boards in secluded areas along walls, behind objects, and in dark corners. Read the Pest Notes: House Mouse for more information.
Rats
The most troublesome rats are two introduced species, the roof rat and the Norway rat. Knowing which species is present is key in effective management. Norway rats arelarger than roof rats but usually have smaller ears and tails. When Norway rats invade buildings, they can commonly be found in the basement or ground level. They create burrows, holes in the ground, along buildings and beneath wood or garbage piles. Roof rats are excellent climbers so they can commonly be found in attics, walls, ceilings, and other elevated surfaces. They nest above ground in trees, shrubs, or dense vegetation. To learn more about rats, see the Pest Notes: Rats.
Of course, rats and mice aren't the only rodents you might find around your home and landscape. You may also encounter other rodent pests such as Voles (Meadow Mice),Deer Mouse, Gophers, Ground Squirrels, or Tree Squirrels.
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- Author: Niamh M Quinn
Where is rodenticide exposure in wildlife coming from? Is it from use by residents or farmers? Applications by marijuana growers? Or from applications by qualified and trained structural pest control professionals? These questions are being asked by state legislators and regulators, special interest groups, and state pest associations across the country.
However, even though we don't fully know where all the exposure is coming from, action is already being taken to restrict the use of rodenticides in urban areas. In 2020, California legislators placed a moratorium on almost all uses of second-generation anticoagulant rodenticide. And local jurisdictions have also added restrictions to rodenticide use. For example, in southern California, the California Coastal Commission granted special approval to the city of Malibu to ban all uses of rodenticides.
What's being done?
Researchers at the University of California Division of Agriculture and Natural Resources (UC ANR) South Coast Research and Extension Center in Irvine have been examining some of these questions over the past seven years. UC ANR's Human-Wildlife Interactions Advisor Dr. Niamh Quinn and colleagues have looked at urban coyotes' exposure to anticoagulant rodenticides (ARs), which active ingredients they were exposed to, and the amounts of AR exposure.
Almost all coyotes examined had been exposed to at least one anticoagulant rodenticide and usually, multiple active ingredients (Table 1). Some were exposed to low amounts of ARs and some were exposed to very high levels. However, less than 1% of the coyotes examined had died from AR exposure. Recent studies on the sublethal effects of exposure have not shown any clear links between AR exposure and sublethal impacts (such as reduced body condition or parasite load). There is also no link between AR exposure and mange in coyotes in urban southern California.
Do coyotes eat rats?
The diet of the urban coyote in southern California was questioned, specifically “Do they eat roof rats?” and “If they don't eat roof rats, how else could they be getting exposed to anticoagulant rodenticides?” It turns out that coyotes do eat rats (Figure 1). They eat a variety of other things too, but rats are among their preferred mammalian prey items, along with rabbits and domestic cats (Table 2).
In one of the first studies of its kind, we examined which animals were actually visiting rodenticide bait stations. We were surprised to find that in southern California, it is mostly roof rats, rather than nontarget animals. This was confirmed in another study sponsored by BASF. In southern California, less than 1% of mammals entering bait stations in urban area were nontarget wildlife. This is good news!
However, if pest management professionals are using anticoagulant rodenticide and are exposing just roof rats, and coyotes are eating said rats, does this mean that legal applications are responsible for the urban coyote AR exposure?
Another interesting finding from these studies concerned how rats use bait stations. With non-toxic baits used during this study, we photographed rats entering only 59–70% of the bait stations, suggesting that roof rats may be reluctant to enter bait stations, even when no rodenticide was present. Even in yards where rats eventually entered stations, it took 7 to 8 days for them to first encounter the bait directly.
What does this mean?
Because the first mortalities from anticoagulant rodenticide might not occur for several more days, pest management professionals should be prepared to communicate these possible delays to their customers. This will prevent customers from becoming impatient and taking more drastic (and potentially illegal) measures when results are not immediate.
Tracing applications of anticoagulant rodenticides
The ability to trace the applications of anticoagulant rodenticides has been lacking, but we may have developed a method to trace AR movement. We have created a bait that can be traced up multiple levels of the food chain. Therefore, we will be able to finally trace the rodenticide bait from its point of application to see if a legal application of anticoagulant rodenticide ends up in multiple levels of the urban and suburban food chain.
Two separate studies were conducted to see where animals exposed to anticoagulant rodenticides die and what scavenges them. One was conducted by Dr. Roger Baldwin in an agricultural setting and one by Dr. Paul Stapp from Cal State Fullerton in the suburban environment. Dr. Baldwin discovered that ground squirrels exposed to first generation anticoagulant rodenticides were mostly dying below ground (Figure 2). Dr. Stapp discovered that rats left in backyards are scavenged on by all sorts of animals including crows, skunks, opossums, and domestic cats. After 7 days, almost all (65%) of the carcasses had been either partially removed or removed completely.
Do coyotes and other large predators also scavenge rats? In research conducted in Europe, 92% of dead rats were inaccessible to large predators and scavengers. It is thought that rats killed by brodifacoum in and around farm buildings don't seem to present a major secondary exposure risk to large vertebrates.
What is next for rodenticide research?
We are developing methods to monitor rodenticide exposure in wildlife in a more meaningful way. The Quinn Lab and other institutions are working on methods to sample for rodenticides in live mammals and birds of prey with the aim of being able to detect any population -level impacts of rodenticide exposure. These methods will provide a mechanism by which rodenticide exposure can be monitored in live populations.
There is a huge need for data-driven mitigation measures for rodenticide exposure in California. We have been testing the efficacy of different management practices. We are testing trapping only, second-generation anticoagulant only, and a mix of both trapping and anticoagulant rodenticide. Using a combination of tracking rodents by collaring them and measuring how long it takes them to die, and by using tracking tunnels, we are measuring how quickly and how effectively these management options manage roof rat populations in southern California.
A mutation associated with second-generation anticoagulant rodenticide resistance, the Y25F mutation, has been found in roof rats in California. We don't know what this discovery means for rats in California. We need to explore more and find out to what extent they are resistant. Resistance management is essential for prolonging the life of all pesticide active ingredients.
Rodent management is complex, time consuming and we are tackling the unknown. We know more about polar bears than we do about commensal rodents. We need to know more to address inadequacies in rodent management. To reduce the amount of secondary AR exposure in the environment, it is necessary to ensure that rodent populations do not rebound and that they are not continually being exposed to active ingredients that can bioaccumulate in the food chain. If predators continue to eat commensal rodents, it is important to figure out ways to reduce the number of them that are exposed to rodenticides.
What does the future of rodent management look like?
It is important to continue work with municipal managers, schools, and customers to ensure that they do their parts. Exclusion and sanitation must be important components of a rodent management plan, especially as there continue to be restrictions on rodent management tools. In some countries, the sale and use of glue boards to catch rodents are prohibited. Certain snap traps have failed rigorous testing in some countries and are considered to cause unacceptable pain and suffering so are prohibited for use. It is important that pest management professionals use tools according to labels and trapping specifications. PMPs must rely on safe and effective methods.
Managing rodent populations such as roof rats is increasingly difficult since there are expanding restrictions on management tools and a dearth of applied research on commensal rodents. To solve these issues, we must find more sustainable and effective management practices.
Our funders and collaborators for these research projects were Cal State Fullerton, the Pest Management Foundation, the California Structural Pest Control Board, the National Wildlife Research Center, California Department of Pesticide Regulation, California Department of Food and Agriculture, and the Anticoagulant Taskforce.
[Originally featured in the Summer 2022 edition of the Green Bulletin Newsletter for structural and landscape pest professionals.]
/h2>/h2>/h2>/h2>/h2>/h2>- Author: Elaine Lander
Annually on February 2, groundhogs get a lot of coverage. Groundhogs, also known as woodchucks, are burrowing rodents often found in the eastern United States. But in California, any shadows from burrowing rodents are unlikely to be a groundhog. Here in the Golden State, you will find other types of burrowing rodents including pocket gophers, ground squirrels, voles, and Norway rats. Though not rodents, moles are another burrowing animal that you may encounter in gardens and landscapes.
See the following UC IPM Pest Notes to learn more about these burrowing vertebrate pests.
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