As you may know, Groundhog Day is observed on February 2nd to predict if there will be an early spring or if six more weeks of winter are in order. Groundhogs are large, ground-dwelling rodents found mainly on the East Coast that can cause severe damage to landscapes, gardens, and structures.
While California doesn't have these future-predicting rodents, the West Coast is home to groundhog relatives and look-alikes that are often considered pests in our landscapes and homes. These include other destructive, burrowing rodents like pocket gophers, ground squirrels, voles, Norway rats, and the invasive aquatic rodent, nutria.Though not rodents, moles are another burrowing animal that you may encounter in gardens and landscapes.
Burrowing animals and vertebrate pests in general are difficult to manage, especially in and around our homes and landscapes. The safest and most effective way to control these pests is by trapping, exclusion, and habitat modification.
To learn more about vertebrate pests in and around the home and garden, see UC IPM's vertebrate Pest Notes publications or visit the Wildlife Pest Identification Tool for help identifying vertebrate pests and finding management solutions.
- Author: Sonia Rios
The roof rat (Rattus rattus, also known as a citrus rat, fruit rat, black rat, or gray rat) is an introduced species of rat native to southern Asia. It was brought to America on the first ships to reach the New World. This is the same species that carried the bubonic plague around the world and is the reservoir host for murine typhus, which is a disease that is transmitted by fleas. This primarily nocturnal vertebrate is a pest in citrus, nut orchards and other tree crops. In citrus, it builds leaf and twig nests in trees or it can nest in debris piles, thick mulch pile on the ground, or in shallow burrows under the tree. In livestock feed yards and barns, roof rats often burrow and hide under feed bunks or in the hay bales. Adult roof rats range from 12-14 inches long (30-36cm) and weigh 5-10oz. (150-250g) (UC IPM 2017). The large, sleek rat has a pointed muzzle and hairless scale-covered tail that can be longer than the body and head combined.
DAMAGE
A rats gnawing can cause some serious damage to just about anything, electrical wires, wooden structures, and they tend to not be picky about which agriculture crop to invade. Roof rats often feed on citrus, avocados, and other fruits, sometimes leaving hollow fruit skins hanging on the tree. In tree crops, they can girdle limbs or stems, leading to mortality to part or all of a tree. After harvest, they damage fruit and nuts in bins by chewing them and leaving excrement. This can cause major esthetics damage to fruit and become a food safety issue. Since rats are active throughout the year, and mostly at night, this can be a challenge to growers and can become infestation because of their quick gestational period of 3 to 4 weeks.
MANAGEMENT
Cultural Control
Because roof rats are such good climbers, swimmers, and hitchhikers it is hard to completely exclude them from your grove or orchard. Fruit trees should be isolated, not touching fences, overhead wires, or the scaffolds or branches of other trees. Roof rats will run along fence stringer boards or support poles, phone and cable TV wires, and tree branches to reach your fruit tree. Lower branches of the tree should never touch the ground. Reducing shelter and nesting opportunity sites of rats is crucial. Eliminate debris and woodpiles and store materials neatly off the ground. Thin and separate non-crop vegetation around orchards, such as weeds and remove dead wood from fruit trees, especially in citrus and avocado (UC IPM 2017). A low-hanging skirt of drooping branches give the rats additional access routes and provides them with protective cover while feeding. It's best to prune tree skirts so that the ground under them is open and visible. This lack of cover makes the rats uncomfortable and more susceptible to predators such as snakes and birds of prey.
Sanitation is also an important component to an IPM program. Use or remove all fallen fruit, do not leave any fruit behind, as the roof rat is an opportunist and will take advantage of the mess left behind.
Monitoring and Treatment Decisions
According to the UC IPM guidelines, the use of elevated bait stations containing 0.005% diphacinone*-treated oats (sold at some county agricultural commissioner's offices) is highly effective at controlling roof rats in orchards. Secure bait in a bait station before placing in trees on limbs 6 feet or more above the ground. Placing the bait in a secure bait station will prevent bait from dropping to the ground and creating a hazard for non-target species. Bait can only be applied during the non-bearing season, so growers must take a proactive approach to managing problematic rat populations (UC IPM 2017).
Trapping
Rat-sized snap or wooden box traps placed in trees are also effective, although a more time-consuming control option. Do not use glue board traps outdoors, as birds, lizards, and other non-target wildlife may be trapped. Rats are wary, tending to avoid baits and traps for at least a few days after their initial placement. Fasten traps to limbs and bait them with fruit or nut meats, but do not set the traps until after bait is readily eaten. Be aware that certain types of rat baits for use inside buildings (such as sticky traps) are not labeled for use outdoors in orchards; these are hazardous to wildlife and should not be used.
Preventative care, sanitation and scouting for rat's nests or damage is the easiest way to stop a problem before it becomes a problem. For more information regarding the roof rat, please visit the UC IPM website: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74106.html.
Baiting *Be sure to identify the species of rat present to avoid killing non-target or protected species.*
- Author: Rob Warren
- Contributor: Jeannette Warnert
Veterinarians at the University of California, Davis, warn pet owners to be careful about using rat poisons and similar compounds.
In recent weeks, veterinarians at the UC Davis William R. Pritchard Veterinary Medical Teaching Hospital have seen a spike in accidental rodenticide poisonings. In the last two weeks of August alone, they diagnosed and treated six canine cases.
If not treated, a dog can die within a week of ingesting rodenticides.
"This is an all-too-common occurrence," said Karl Jandrey, assistant professor of clinical small animal emergency and intensive care at UC Davis. "People are trying to get rid of unwanted rodents, but are not realizing what these toxins do to the other animals who share that environment."
Keeping pets safe
Using proper pest control techniques can help keep family pets safe, said Roger Baldwin, UC Cooperative Extension advisor with the UC Integrated Pest Management Program. Baldwin, a wildlife pest management expert, is based at the UC Kearney Agricultural Research and Extension Center in Parlier.
Dogs can be affected by rodenticides two ways: by eating the poisoned bait or by eating an animal that was poisoned. Both can have serious consequences.
Home improvement stores like Lowes and Home Depot, and even grocery stores, carry a variety of products that may be used to control unwanted rats, mice, pocket gophers and ground squirrels. If the unwanted animals are inside the house, Baldwin recommends using traps rather than poison.
"If a poisoned animal dies behind a wall, you can't get it out and you have to live with the smell for weeks or months," Baldwin said.
Also, before baiting outdoor pests, Baldwin suggests making sure they are not also going inside buildings. If they are, find all potential access points and close them up.
If resorting to poison baits, buy a new product at the store and carefully read the label to understand when, where and how it can be used. Because of rapidly changing restrictions in recent years, old products in your garage or shed could be outdated.
Pocket gopher bait must be placed in the gopher's underground burrow. Even there, Baldwin said, certain dogs will dig up dead pocket gophers if they are close enough to the surface. Families with digging dogs will likely want to choose gopher traps. For ground squirrels, baits can be placed in bait stations or scattered very thinly on the ground through broadcast or spot treatments.
"When you use broadcast or spot treatments, there is relatively little danger to dogs or cats," Baldwin said. "But I would opt to use bait stations in my yard if I had pets running around, just to be on the safe side."
Some rodenticides contain ingredients that are anticoagulants, which slow the clotting of the blood. When dogs ingest these poisons, the active ingredients concentrate in the liver where they interfere with vitamin K storage and the production of blood clotting factors.
At UC Davis' veterinary teaching hospital, dealing with accidental poisoning by an anticoagulant rodenticide can require around-the-clock care with treatments in the intensive care unit to replenish blood clotting factors with fresh frozen plasma and replace vitamin K. If administered early enough, this treatment usually leads to a full recovery. Other rodenticides (e.g., bromethalin, cholecalciferol, strychnine and zinc phosphide) do not have antidotes, so treatment is more difficult.
One patient recently treated at UC Davis was Mocha, a one-year-old Belgian Malinois from Winters, Calif. Mocha had gotten into d-CON, a common rodenticide available at hardware stores.
Luckily, Mocha was brought to the veterinary teaching hospital in time. She responded well to treatment and was able to go home in two days.
"We are grateful for the care Mocha received at UC Davis," said Ken Shaw, Mocha's owner. "Like most dogs, Mocha is adventurous and likes to get into things she shouldn't. But after the treatment at UC Davis, she was home within a few days, happy and playful once again."