Rats and Rat Control
Several California mosquito and vector control districts offer their residents general information on rodent control. This information on roof rats emphasizes conditions in the City of Davis and what preventative practices citizens can do to prevent or reduce rodent problems.
The roof rat or black rat (Rattus rattus) is responsible for having spread the plague in Europe during the Middle Ages. Here in Davis it poses both a health and safety hazard. Besides plague, roof rats may spread other diseases to humans like murine typhus, leptosporosis, salmonellosis, trichinosis and rat bite fever. They can also spread diseases to domestic animals and are suspected of transmitting ectoparasites from one place to another. Besides consuming and contaminating stored food and feed they will gnaw on wiring (posing a fire hazard), wood, and tear up insulation for nesting material. Rats will feed on fruits and vegetable in many gardens as well as damaging young trees by feeding on their bark. Unprotected compost piles as well as pet food are common food sources for them in our neighborhoods.
The roof rat’s cousin, the Norway (or sewer) rat (Rattus norvegicus) is a burrower. It is larger than the roof rat and prefers ground level dwellings. The following chart highlights the differences:
Roof rats are nocturnal like their cousins the Norway rats, but the aerial nature of the roof rat is what distinguishes them and has implications for their control. Roof rats prefer to forage above ground; they are agile climbers and travel through trees, vines, rafters, wires and rooftops. They use trees and utility lines to reach food and enter buildings. They can also be found foraging in dense ground cover. Secluded areas above ground are ideal for nesting such as attics, overhead garage storage, in the vine cover of fences or buildings and in wood piles. They prefer non-deciduous trees or trees with hollow cavities and crowns of palm trees, especially when old fronds are not removed.
Roof rats have high reproductive potential, with 3 to 5 litters/year and 5 to 8 pups/litter.
Prevention through methods of exclusion and habitat modification can provide long term control by preventing infestation. Exclusion from homes or buildings is difficult since they are excellent climbers and can get through very small openings. Rodent proofing a home or building requires sealing all possible entry points especially where pipes or utility lines enter a building.
- Seal openings ½ inch wide or greater to the outside of a structure with concrete mortar, steel or copper wool or metal flashing
- Cover attic and foundation vents with ¼ inch wire mesh or heavy wire screen
- Use rat guards made from sheet metal 18-24 inches wide to prevent the rats from climbing
Habitat modification makes an area less suitable and less attractive to roof rats. They are very sensitive to changes in their environment -- even slight habitat changes may cause these rodents to move or redirect their activity patterns. Improving general sanitation is a big step towards eliminating food sources:
- Secure garbage in rodent proof containers
- Store materials properly
- Harvest fruits and vegetables in a timely manner and pick up fallen fruit promptly
- Remove attractants such as pet food, bird feeders and standing water.
- Compost in closed compost containers
Eliminate or reduce protective cover that these rodents use:
- Prune shrubs so that the ground below is visible
- Mow, trim or remove ground cover plants that are over 1 foot in height
- Stack firewood or lumber at least one foot away from walls and fences and at least 18 inches off the ground
Roof rats travel along vines, tree branches, fences and utility wires. Eliminating these aerial pathways can dramatically reduce roof rat travel.
- Eliminate or severely prune back vines growing on buildings or fences
- Remove tree limbs that overhang roofs
- Prune trees so that the branches do not touch fences, overhead wires or branches of adjacent trees
- Prune skirts of trees so that branches do not hang down to the ground
These preventive practices will help in reducing roof rat infestations.
- UC IPM - Rats
- University of Arizona - Roof Rat Controls Around Homes and Other Structures
- Marin/Sonoma Mosquito & Vector Control District - Rats: Prevention and Control
Weeds are simply plants that are undesirable where they are growing. They take the light and nutrients needed by the other plants which results in limited growth of the wanted plants.
|Weeds are known to be unsightly, however some weeds, such as corncockle (shown right), are used as garden plants. This flower was a common field weed but, due to its beauty, is now used as a garden plant.||
Some weeds, on the other hand, have thorns or prickles or can even be poisonous such as oleander (shown right) that can lead to skin irritation if touched. They can also attach to clothes as well as animal fur.
Flame weeding is used as an alternative to harmful pesticides. It works by killing the weeds with an intense wave of heat.
All plants are made up of tiny cells that are filled with water. By delivering a thin blast of heat directed at the stalk and young leaves, the heat will boil the water inside the cell, rupturing them. After this happens, nutrients and water for the plant cannot move from roots to leaves and results in the plant withering and eventually dying. By destroying the cell structure, the weed will not put energy towards growth. Flame weeding is nearly 100% effective on broad leaf weeds that are caught early.
Flame weeding will be controlled and done by trained city staff on city properties. If you have any questions and/or concerns about this project, please contact the City of Davis Public Works Department, at (530) 757-5686 or email@example.com.
Mulching is one of the simplest and most beneficial practices you can use in the garden. Mulch is defined as a protective layer of material that is spread on the top of soil.
Mulch comes in two different types: organic and inorganic.
Some examples of organic mulch are grass clippings, straw and bark chips.
Inorganic mulches include stones, bark chips and plastic.
Either type of mulch will provide these benefits:
- Protect the soil from erosion
- Reduce compaction from the impact of heavy rains
- Conserve moisture, reducing water use
- Maintain a more even soil temperature
- Prevent weed growth
- Keep fruits and vegetables clean
- Keep feet clean, allowing easy access to the garden even when it is damp
- Provide a “finished” look to the garden
Organic mulch also improves the condition of the soil. As the mulch slowly decomposes, it provides organic matter which helps keep the soil loose. Loose soil improves root growth, increases the infiltration of water and also improves water-holding capacity of the soil. Organic matter is a source of plant nutrients and it also provides an ideal environment for earthworms and other beneficial soil organisms.
Inorganic mulches have their place in certain landscapes, but they do lack the soil improving properties of the organic mulch. Due to the persistence of inorganic mulch, it may be difficult to remove if you decide to change your garden at a later date.
Newspaper mulching is a highly effective, non-toxic way to subdue annual grasses and weeds:
First, wet the soil. Then lay thick layers of overlapping newspaper.
Wet the newspaper to keep it in place...
Then apply organic mulch.
For tougher weeds, use cardboard.
Soil solarization is a nonpesticidal method of controlling soilborne pests by placing UV resistant plastic sheets on moist soil during the months of high temperature. The plastic sheets allow the suns heat to be trapped in the soil, heating the upper levels. This will increase the soils temperature to levels that kill most weed seeds and seedlings. This process also improves the soil structure and increases the amount of Nitrogen and other essential plant nutrients. Large increases in plant growth often occur in solarized soil. In order to solarize your garden, you must cov¬er the soil for 4 to 6 weeks during the hot period of the year when the soil will receive the maximum amount of direct sunlight. The best time to do this is in June and July. If this is done properly, the soil can reach a temperature of up to 160 degrees on the surface and up to 100 degrees 3 inches deep. Solarization is by far, the most effective way home gardeners have to reduce or eliminate soilborne garden pests. The benefits are healthier and more productive flower and vegetable gardens. This process is better for your plants and the environment since there are no pesticides used.
For more information go to UC IPM Online.
Insects are one of the most important and diverse forms of life on earth. They account for more than half of all known living organisms on the planet. Many insects are beneficial to humans and the environment providing products such as honey, wax, silk and food for human and animal consumption. They also serve as pollinators, scavengers, decomposers, recyclers and natural enemies of pests.
Insect pests annoy humans and animals, transmitting diseases, destroying crops, ruining stored food and wooden structures. The following are common insect pests and least toxic forms of control:
- Store food in airtight containers
- Keep counters clean and dry
- Caulk cracks and weather strip doors and windows where ants enter
- Keep pet dishes in soapy moats
- Sticky barrier
- Teflon barrier
- Tree wrap
Least Toxic Chemical Controls:
- Bait stations -- with boric acid, hydramethylnon, fipronil or arsenic
- Botanical sprays -- mint, cedar, orange and other herbal oils
- Borate-based insecticides -- borate liquid ant bait, borate gel bait, borate granular ant bait
- Diatomaceous earth (DE) -- baited DE or DE with pyrethrin
- Insecticidal soap
- Silica aerogel
- Store food in refrigerator or sealed containers.
- Keep counters and food storage areas clean.
- Keep areas dry
- Seal crack and crevices
- Caulk cracks and weather strip doors and windows
- Teflon barriers
- Sticky traps
- Pheromone traps
- Glue board traps and vacuums
Least Toxic Chemical Controls:
- Bait stations with abamectin, borate-based insecticide, hydramethylnon, fipronil or sulfluramid
- Botanical sprays: orange, mint or herbal oils
- Borate-based insecticides: liquid ant bait, gel bait, granular ant bait
- Diatomaceous Earth (DE): baited DE or DE with pyrethrin
- Hydroprene Insect Growth Regulator
- Silica aerogel
- UC IPM - Cockroaches
- Our Water, Our World - Keeping Cockroaches Out of Your House
- Beyond Pesticides - Least-Toxic Control of Cockroaches
Wasps & Yellowjackets
- Seal holes and cracks in walls, foundations and roofs to prevent wasps from entering
- Cover attic and crawl space vents with fine mesh insect screen
- Wasps scavenge for meat and sweet foods and drinks in outdoor garbage and recycling bins
- Clean recyclables before storing them
- Keep garbage cans clean and tightly covered, or seal all food garbage in plastic bags.
Contact the Sacramento-Yolo Mosquito & Vector Control District at 1-800-429-1022. Depending on their workload they will respond to Wasp control calls. They do not remove bee hives.
- UC IPM - Yellowjackets and Other Social Wasps
- Our Water, Our World - Controlling Yellowjackets Around Your Home
Spiders are beneficial arachnids that feed on insects. Most are harmless to humans and should be tolerated around the home and garden. If they are inside the home:
- Vacuum them up along with their webs
- Capture them with a container, slip a sheet of paper over the opening, and release them outside
- Keep them out by caulking cracks and crevices
- Reduce their food supply by installing screens, replacing porch lights with yellow bulbs, and ripening fruit in sealed paper bags
- UC IPM - Spiders
- Our Water, Our World - Living with Spiders
- Beyond Pesticides - Least-toxic Control of Spiders
Sticky Sidewalks: Woolly Hackberry Aphid
As summer approaches, so do the woolly aphid problems on the Chinese hackberry trees.
This aphid infests hackberry, especially Chinese hackberry (Celtis sinensis), throughout the state. This aphid was accidentally introduced into the United States in the late 1990s, and also occurs from Florida to Texas, and northward to at least Tennessee. Its copious honeydew excretions create a sticky mess, and promote the growth of blackish sooty mold on leaves and on surfaces beneath infested trees.
See UC IPM - Hackberry Woolly Aphid for information about woolly aphid life cycle and control.
Living with Urban Wildlife
Davis has many wonderful mature trees, densely vegetated greenbelts and native open space areas. These areas are attractive to a wide variety of wildlife species. Having wildlife live so close to home is a great way to watch and enjoy our fellow Earthlings. However, wildlife can sometimes cause problems at home. Reducing conflict with wildlife at home takes patience and persistence, but in the end both you and your wild neighbors will be happy and healthy. Below are some common urban wildlife species and ways to help reduce conflict at home.
Much joy can be had watching these busy little guys romp around. However, like their rodent cousin the rat, squirrels can cause damage around the house and in the garden.
- Do not feed squirrels.
- Seal openings to the outside of a structure that are = ½ inch wide with concrete mortar, steel or copper wool or metal flashing.
- Cover attic and foundation vents with ¼ inch wire mesh or heavy wire screen.
- To protect fruit and nut trees, use squirrel guards made from sheet metal 18-24 inches wide around the trunk to prevent them from climbing up trees.
- Deter squirrels by cutting back vegetation at least 8 feet from trees you wish to protect.
- Prevent ground squirrels from tunneling into your garden by installing wire mesh 1-2 feet below plant beds.
- Motion activated sprinklers (ex. Scarecrow®) have proven very effective at deterring squirrels and other unwanted animals.
Raccoons, like humans, are constantly tending to the basic needs for food and shelter. They find both near our homes. While they may appear to be just curious, they are probably in search of food. Raccoons are usually not aggressive unless sick, cornered, mating, or with young.
- Do not feed raccoons.
- To raccoon-proof a garbage can, fasten the lid securely with rope, bungee cords, chain, or even weights.
- Sprinkle lawns or planters with cayenne pepper to discourage grub hunting.
- Motion activated sprinklers (ex. Scarecrow®) have proven very effective at deterring raccoons and other unwanted animals.
- Control grub populations so that raccoons will not be drawn to your lawn in the first place. Organic grub control products work very well.
- Fasten bird netting over garden plants. It is easier for raccoons to dig elsewhere than to remove the netting.
- Improve existing fences by enclosing any open area between the bottom of the fence and the ground, or install fence extenders facing outward at a 45-degree angle on top of each post, with two or three strands of wire strung between them.
- If the area is fairly small, try sinking jars filled with ammonia into the ground, with sponges as wicks. Be sure the jars are anchored in the soil to prevent spilling. Or try hanging socks filled with mothballs.
- Serious gardeners might consider an electrified fence. String ordinary, 2-millimeter galvanized wire along insulator posts around the perimeter. The wire should start about 8 inches above the ground to prevent crawling underneath and lines should be spaced close together so animals cannot reach through. Connect the wires to an approved fence charger with alternating current not exceeding 12 volts, which can be purchased relatively cheaply at feed stores. Be sure to check with the Building Department for installation guidelines and/or limitations.
Turkeys can be fun to watch and they help to keep pests like slugs and snails reduced. However, they can also tear up landscaping in search of food and pose a traffic hazard when crossing busy streets.
- Do not feed turkeys.
- If turkeys begin feeding under hanging bird feeders, remove the feeders until the turkeys leave the area.
- If turkeys are causing problems in your yard, install motion-detecting sprinklers.
- Wild turkeys typically will not enter yards with dogs.
- If confronted by a wild turkey that has lost its fear of humans, an open umbrella may help steer it out of your path.
- Depredation permits are required to kill wild turkeys that are causing property damage. To get a depredation permit, contact the local Department of Fish & Game office (916/358-2900).
Sparrows, Finch, Swallow, Rock Pigeon, and other structure nesting birds
Sharing your home’s roof or eves with a family of nesting birds can be a wonderful experience, however, nests and young birds can be messy. It is important to note that bird nests are protected by law. A homeowner with an undesirable nest would need to wait until after the breeding season to remove a nest should they discover one with eggs. To prevent unwanted nests, employ deterrents that prevent the nests from being built in the first place.
- Install visual deterrents, such as strips of metallic ribbon, old CDs or DVDs or predatory mimics (ex. Terror Eyes®), to locations were birds build nests.
- Install small wire mesh along eves or terracotta style roofing tiles.
- Be vigilant about swallow nest building activity in the early spring. Use a hose to wash down partially constructed nests on a daily basis.
Like turkey and other urban wildlife, crows can be very interesting to observe. They are typically spread out across the region during the nesting season but can form large, noisy and messy roosting colonies during the fall and winter. To help prevent a crow colony from habituating to your tree:
- Install visual deterrents, such as strips of metallic ribbon, old CDs or DVDs or predatory mimics (ex. Terror Eyes®), to upper branches of roost tree.
- Spray a high pressure hose up into tree at roost time to keep crows on the move. This may need to be done nightly to eventually break crow site fidelity.