- Author: Ben A Faber
UC IPM recently hosted a webinar on rat management presented by Dr. Niamh Quinn. During this webinar attendees were able to ask the expert their burning questions about rats and their management. Below are responses to common questions from the webinar.
To view the recording of this webinar, visit https://www.youtube.com/watch?v=IuKU6izZozo. Or visit the Pest Notes: Rats fact sheet that was recently revised by Dr. Quinn.
Rat Identification
Q: How do I know whether I have a roof rat or a Norway rat?
A: The roof rat (also called the black rat, house rat, or ship rat) is smaller and sleeker than the Norway rat, with a tail that is longer than the head and body combined. Roof rats are agile climbers and usually live and nest aboveground in shrubs, trees, or dense vegetation such as ivy.
The Norway rat (also called the brown rat, sewer rat, or barn rat) is a burrowing rodent that is generally larger and stockier than the roof rat. Their burrows may be found along building foundations, beneath rubbish or woodpiles, and around gardens and fields.
When the two species occupy the same building, Norway rats typically occur in the basement and ground floors while roof rats occupy the upper floors and attics.
Q: How can you distinguish protected woodrats from Norway and roof rats?
A: Like commensal rats, pack rats (woodrats) consume various food items, including fruits and nuts. An easy way to distinguish pack rats from Norway and roof rats is to visually examine their tails. Woodrats have furry tails, while commensal rodents have scaly and mostly hairless tails.
Trapping
Q: Should you wear disposable gloves when handling rat traps?
A: Human scent is not known to have any impact on rat trapping but since rats can carry diseases, it would be best to wear gloves when handling used traps. You should always wear gloves when handling dead rats.
Q: What is pre-baiting and why should you do it when using toxic baits?
A: Pre-baiting means placing bait in the trap without setting the trigger of the trap. Since rats are neophobic (afraid of new things) doing this will allow them to get more comfortable approaching the trap to get the food or other item (cotton, etc.). Pre-bait for 5 days or so and then set the trap to catch the rodent.
Q: Can rat traps be reused?
A: Depending on the type of trap purchased, some are meant to be reused while others are single use. Snap traps, for example, can be used over and over again.
Q: How can you secure or anchor down rat traps?
A: Rat traps should be secured down to effectively catch rats and find the traps later. They can be screwed into a piece of wood, such as 2x4 lumber, which you can reuse and easily move traps to new management areas. Putty or tape can also work.
Q: How can you prevent wildlife from being harmed while trying to manage rats?
A: Trap rats at nighttime when songbirds are not active to prevent them from being caught in traps. When using toxic baits, place them in bait stations to make them less accessible to wildlife.
Q: What should you do with live-trapped rats?
A: Live-trapped rats must be humanely euthanized or released immediately in the area where they were trapped. Releasing rats is not recommended, as they will continue to cause damage. Animals can be humanely euthanized by a shot to the head if it is legal to discharge a firearm in the trapped area or a firm blow to the head. Drowning is not an acceptable method of euthanasia, and it is illegal under California State law.
Repellents and toxic baits
Q: What can be used to deter or repel rats? I've heard of using coyote urine, mint, LED lights, and ultrasonic devices.
A: No plants have been proven to deter rats from an area and high frequency ultrasonic sounds are not effective for controlling rats in homes and gardens. Human or coyote urine or scent do not repel rats.
Q: Can homemade mixtures be used to manage rats?
A: Only registered pesticide products can be used to manage rats.You should not try to create your own toxic baits at home with household ingredients.
Prevention and other management methods
Q: How can you prevent rats from chewing wires in vehicles and other powered equipment?
A: Use a weighted car cover to dissuade rodents from accessing the engine and chewing wires. To be effective, the cover must touch the ground, forming a seal all around the vehicle.
Q: Can predators like owls, hawks, or cats effectively manage rats?
A: Predators, especially cats and owls, eat rats and mice. However, predators in general cannot significantly control animals that are good colonizers and prolific reproducers (of which rats are extremely good examples!). Furthermore, if cats or other would-be predators are fed outdoors, their food serves as a strong attractant and a continuous food source for rats and mice in the area.
Q: What can home gardeners do to keep rats out of the garden?
A: Sanitation is fundamental to rat control and must be ongoing. Keep pipes, lumber, firewood, crates, boxes, gardening equipment, and other household goods off the ground. Clean up leaves and fallen fruit in backyards. Thin or remove dense vegetation, such as ivy, around or on homes. Excluding rats from garden beds is very difficult. Fencing or enclosing raised beds with wire mesh may provide some management but it is not guaranteed.
Q: Should I even attempt to control rats in my backyard if I live in a neighborhood or community where there are lots of rats and my neighbors don't take action?
A: Successful rat management in a neighborhood does require community-wide effort to remove harborage and food sources. But you can reduce the likelihood of rat infestations or damage to your property if you follow best management practices (i.e., sealing gaps larger than ½ inch, removing wood piles or items stored on the ground, thinning dense vegetation around homes, etc.).
- Author: Ben A Faber
Rodents, particularly rats, have wreaked havoc in California orchards and vineyards this year. Some growers have reported yield losses, damage to trees and destruction of irrigation lines, electrical wiring and other infrastructure.
Farmers face soaring costs to replace what has been destroyed or damaged, but also to control populations of the pests.
The rodent problem was initially reported in San Joaquin Valley nut orchards. But Roger Baldwin, a wildlife specialist and expert in rodent management at the University of California, Davis, said the problem is more widespread. He has heard about rodent damage on the west side of the Sacramento Valley and along the Central Coast, particularly in citrus orchards.
One reason for increased rodent activities this year could be abandoned orchards, which provide plenty of food and shelter for rodents to proliferate, Baldwin said.
“Rodent damage, if ignored, can lead to substantial losses,” Baldwin said.
Rats and other rodents can damage trees by removing the bark, which can cause disease and, if severe enough, kill the tree. The animals also chew through drip hoses.
Baldwin has studied different rodenticides for controlling roof rats in almond orchards. He found that using 0.005% diphacinone-treated oats inside elevated bait stations resulted in more than 90% reduction in rat activity.
Baldwin recommended constructing a bait station from PVC pipe and placing it roughly 4 feet above ground by attaching the stations to branches. He placed stations either 98 feet or 165 feet from each other throughout the orchard. Using 165-feet spacing reduces the cost, but efficacy drops to about 75%, he said. “The closer the stations are, the more likely it is that it's going to work,” he said.
After knocking down much of the rat population using bait, Baldwin placed trapping tunnels, or snap traps, 250 feet apart throughout the orchard. During a five-month period, the tunnels further reduced rat activity by 90% to 95%, he said.
After trapping, growers should still do periodic monitoring, Baldwin said, as some rats will evade the traps over time, and populations may start to rebound.
Using a diphacinone application remains a good strategy for initial knockdown of rodents, Baldwin said. He added there are other tools for keeping populations down for a longer period. One is burrow fumigation, with aluminum phosphide being the most effective, he said.
Other control measures include pressurized exhaust machines that inject carbon monoxide into burrows. But there's not much data on their effectiveness on rats, Baldwin said. He thinks they probably don't work as well as aluminum phosphide but could provide some relief.
Source: California Farm Bureau
Photo: rat damage to lemon tree
- Author: Pam Kan-Rice
Roof rats are running rampant in California orchards this year, according to UC Agriculture and Natural Resources scientists.
“In pistachio and other nut orchards, roof rats are burrowing and nesting in the ground where they're chewing on irrigation lines, causing extensive damage,” said Rachael Long, UC Cooperative Extension advisor. “They are also nesting in citrus trees, feeding on the fruit and terrifying field workers when they jump out as people are picking fruit. The chewing pests are also girdling citrus limbs, causing branch dieback.”
The wet winter of 2017 led to lots of weed seeds for rats to eat. “Last season, rats were also nibbling on pomegranates, avocados, and other fruit and nut crops, rendering them unmarketable,” Long said.
Holes in the ground around the base of pistachio trees throughout a Yolo County orchard puzzled the grower.
“We looked for ground squirrels, but never saw any,” Long said. “We set up game cameras, but only got birds and rabbits. We put rodent bait in the holes, but the digging didn't stop.”
Long, the pest detective, cracked the case by consulting Niamh Quinn, UC Cooperative Extension human-wildlife interactions advisor based in Irvine. “She informed us that the damage we were seeing was from roof rats.”
Burrowing roof rats sounds like an oxymoron. While roof rats generally don't burrow in urban environments, their country cousins have been known to burrow.
“It's not true that they don't burrow,” Quinn said. “When I worked as staff research associate for Roger Baldwin, UC Cooperative Extension wildlife specialist, that is mostly what we studied, burrowing roof rats in orchards.”
Control measures
Baldwin said, “It seems to be a good year for rats in a number of different areas and crops throughout the state. I've received more questions and comments about rats this year than perhaps the last 10 years combined. As for bait application, putting bait down burrow systems for rats doesn't usually work too well, so I'm not surprised that approach didn't work. Growers will likely have better luck with bait stations in the trees.”
Because the rats climb, Baldwin suggests attaching bait stations to tree branches.
“In addition, elevating the bait stations will eliminate access to bait for many protected mammal species, such as kangaroo rats,” Long said. “The bait diphacinone grain can be purchased from some ag commissioners' offices. This is what Roger Baldwin said they tested and it worked.”
As for the bait stations, they should be designed so that there isn't any spillage for nontarget animals to eat, Long said.
When roof rat outbreaks occur, rodenticides are often needed to prevent crop damage. However, timing is critical as diphacinone use is highly restrictive and not allowed during the growing season, which is beginning as the weather warms.
“Check the product label for application instructions,” Long reminds growers. “It's the law.”
Identifying the pest
One way for growers to identify whether they have roof rats is by the size of the burrows. The nocturnal pests are active above ground in trees and below ground.
“Roof rats can forage away from their nest, so you won't likely find signs of their activity, such as rat droppings outside their burrow, to help identify them,” Long said.
Ground squirrels are active during the day, so they are more likely to be seen, dig holes about 4 inches in diameter and forage above ground near their burrows. Vole and mouse holes are 1- to 2-inches in diameter. Roof rat holes are typically 3 to 4 inches in diameter and might have nut shells in front of them, for example pistachio or almond shells. Rabbits will feed on seedling crops, but do not dig burrows.
Roof rats are prolific breeders that reproduce year-round, according to Baldwin. Females typically have three to five litters per year with five to eight young, enabling their populations to rapidly increase. The omnivores feed on a wide variety of plant and animal materials, allowing them to adapt to any environment, including urban and agricultural lands.
“Rats are sneaky and hard to spot,” Long said. “If you see damage, including digging in the soil but no wildlife, suspect rats.”
For more information on controlling roof rats, download Quinn and Baldwin's free UC ANR publication 8513, Managing Roof Rats and Deer Mice in Nut and Fruit Orchards at http://anrcatalog.ucanr.edu/Details.aspx?itemNo=8513.
For more information about ground squirrels, download the free UC IPM Best Management Guidelines http://www.groundsquirrelbmp.com or UC IPM Pest Note http://ipm.ucanr.edu/PMG/PESTNOTES/pn7438.html.
And there's more on rats in the orchard:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=26570
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=24581
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19525
- Author: Ben Faber
Along the mighty Santa Clara River are planted many lemons and once upon a time many Valencia orange trees. There's lots of wild life along the river which causes some issues with food safety. One of the many creatures are rats and when things dry up they start foraging further and further for food. They really like citrus and can cause a lot of damage. What I first thought was sun burn damage turned out to be rat feeding on the bark and cambium of these lemon trees. The damage wasn't in the right position to be sunburn damage. Inside the canopy, often on the north facing branch.
