Golden Gate Garden

Rats!

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Seems like many gardeners are contending with rats these days. They eat vegetables and have been damaging citrus trees. They gnaw the bark off of citrus trees, or chew off twigs, or chew the rind from the fruit. As promised in this week's column, here is information that was in a recent column about rats, including links to two very good information sheets on the animals:

One reader reported good results from using an aluminum trunk band on a fruit tree trunk. Thsi can help if it is 12 inches wide and there is no other way into a tree. Repellent granules may also help. Traps are effective when used well, and pest-control professionals can be hired to set them. (One way to locate licensed trappers is through the Web site www.wildlife-removal.com). Rat bait is the worst idea, since the poisoned rats are likely to lbe eaten by cats or birds of prey, which will be killed by poisoned rats. 

It is important to understand that urban rats are a community problem, not necessarily solvable by one gardener working alone to protect one tree or one vegetable garden. Rats multiply when they can get into houses, have access to food (garbage, pet food, birdseed, etc.) and have cover (ivy on fences, heavy ground cover, trash). As the lemon rind story shows, if you have rats, your neighbor does too.

City health department inspectors will survey a property for possible attractants and habitats, and advise on how to remove them. They will also cite individuals with documented rat-attracting conditions who refuse to remove them. (To report a rat problem in San Francisco, call 311.) But perhaps a better approach is a community effort, such as a block party to seal up buildings, clean up and get a neighborhood rat problem under control. I found two downloadable rat information sheets that explain the tasks necessary to make a neighborhood rat-unfriendly. One is at the San Francisco Health Department Vector Control site (www.sfdph.org/dph/files/EHSdocs/ehsPublsdocs/pests/Rats_and_Mice.pdf).

The second information sheet (www.hungryowl.org/rodenticide.pdf) is on the Web site of the Hungry Owl Project. This Marin County nonprofit helps Bay Area residents set up barn owl nests so these raptors can provide natural rodent control, and also offers good advice on other environmentally safe ways to control pest rodents.

17 responses to “Rats!”

  1. Zannie

    I have resigned myself to having rats around. My street is at least half restaurants on the ground floor, some of which look questionable, sanitation-wise (and their scores in the windows are not stellar). If I tell my landlord I saw one, he’ll just put poison out. I did at least get him to put it in a box that cats can’t get into, and my cat is not much of a mouser, but that still leaves the problem of other neighborhood cats and birds of prey–and the cruelty to the rats.
    I think it is rats that eat my low-growing tomatoes. But the higher ones they seem to leave alone, and my general theory on pests is that as long as they leave enough for me, we can live in peace.

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  2. pam

    From what I read, the ultrasonic devices don’t work. You do need to find more information. Look for a source of information about this device that isn’t trying to sell it to you instead of buying it based on an ad. Of course it sounds good, an adwriter wrote about it. Hold onto your money.
    About poisoning rats: Even if the poison is in a box the cat can’t get into, the dead rat won’t be. Your cat could be poisoned by eating the dead rat. Traps are a far better solution.

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  3. Naturistman

    We lost at least half our tomatoes last summer what I suspect may have been rats. The tomatoes would have large bite marks in them… and they’d gradually disappear. Our neighbor mentioned he saw (a?) rat scurrying around. I did put out some bait, and it just disappeared too, but the problem persisted. I’m looking for new ideas to deal with them this summer. After months of painstakingly growing the vegetables it’ really s*cks to have them get destroyed like that.

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  4. Randy P.

    I sympathise. Here in Central Florida, many of the neighborhoods were built on old orange groves with lots of orange trees left in place or planted by the new homeowners. A never-ending supply of food. Rats are a constant problem. I have to agree with a previous poster that poison is a last resort. It will kill non target species, and even worse is if the poisoned rat decides to die in your house or garage and you can’t find him. You must be careful with trapping also because it will kill squirrels, etc. They make trap covers to protect dogs, cats, and children from traps. I have made my own in my garage from a cardboard box with small access holes cut out. Kept the neighborhood cats from getting caught at least.

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  5. Tony King

    Allow me to give you some advice that might help with the control of rats especially in a garden. Being an avid gardener as well as a pest control expert I have some knowledge in gaining an acceptable level of control. Firstly the ultrasonic pest repellers do not work and you will be wasting your money on these. My company has never ever successfully used these and to date after 20 years I am still visitng clients who have used these and then called us in. If you are not interested in using poison but would be able to trap the rats an easy solution is to either buy the plastic rat bait stations or make simialar boxes and place break back rat traps inside them away from target animals. It is really quite rare for birds to go into these boxes and the trap should be set inside away from the entrance. If you dont mind using poison you could also purchase the rat bait stations or better still and cheaper us 75cm plastic pipe and cut into 50 cm lenghts and place the poison inside these. The cats will not be able to fit into such a pipe and the poison should be placed in freezer bags so to avoid slugs eating the bait and this will also stop the bait from getting damp. Dont worry about the rats they will take the bait back as it is in the bag.
    I hope this helps

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  6. Pam Peirce

    Hi Tony,
    I think this advice will work, but caution readers not to use poison to kill rodents, since the poisoned animals will kill predators. It is so important to spare the predators. We have learned this when it comes to insects. We try not to poison the lady beetles and parasitic wasps, but gardeners often forget that rodents have predators too. And like predators of insects, they are less numerous than their prey, so their population is more vulnerable to poisons.

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  7. Pest Control London

    In external areas rodenticides work well, but there are new trapping devices that work very well. They are called trap in a box, they catch the rat or mouse in the box with an instant kill and its a very effective alternative to rodenticides.

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  8. PF

    I’m having problems with rodents eating the bark on my meyer lemon tree in SF. I was just reading about peppermint oil repelling mice. Also what about the spray that you put on trees to keep out bugs when you cut a branch? Do you think either would be effective – or other advice? Maybe even planting peppermint at the base of my tree as sort of a companion plant? There are lots of ways to access my tree since it is next to a wall so I don’t think the aluminum sheet would work and I don’t want to use poison. Thank you for any advice.

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  9. Pam Peirce

    Please go to the links in the above post and read them, as they have much helpful information. The most important ways to reduce the numbers of rats is to reduce their habitat and to trap them. There is a lot of good advice about both on the links.
    Many Bay Area gardeners have been having the problem of rats, probably roof rats, eating the bark of citrus. I don’t know for sure if peppermint oil will repel the rats. They aren’t repelled by much. But a number of websites have mentioned peppermint oil as a rat repellant, so it is worth a try. I would try spraying it onto the tree bark every two or three days and see if damage lets up.
    I don’t know what is in the other spray you mentioned, the one you say you spray on pruning cuts. I don’t know of any material still recommended for that purpose. However, whatever it is, if it repels insects, that is not a reason to expect it might repel rats.
    You could try protecting your trunk and larger branches with chicken wire fastened around it loosely and a bit crumpled. You should also be sure to harvest fruit as soon as it is ripe, but I think unless you reduce the population of rats by trapping and/or giving them fewer places to hide, they are going to be a problem.

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  10. Elaine Leithiser

    I have read that lavender works against rats. You can use cotton balls with a few drops of lavender. I also planted several plants around the yard. I think they ate some of my tomatoes in a container last year so I used Tanglefoot around it with bird netting around the cage. It worked but when I used a sticky item in my raised garden it killed a small lizard so I try to only use this hanging up now. I also used critter repellent that included rats on the list. For moles I planted marigold and peppers. Many rodents do not like fragrant herbs so I have planted those also. For snails I use dried egg shells crumbled around the plants. Birds you can hang up old CDs on a string to keep them at bay.

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  11. anthony

    04/24/2014
    i went out side to see my fruit, citrus trees and the peel of my lemons have been eaton away starting from the top ….i also have lots of lizards and don’t want to hurt them
    they eat all the bugs . i want to get rid of the rats or mice ,i can’t use glue traps might get the lizards. i have a humane trap .it seems not to be working .any other ideas?
    so cal

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  12. Karl McCralsy Jr.

    I am trying Tanglefoot* sticky barrier. Its a natural sticky resin imbibed with camphor and castor oil. It has an herbal smell that they don’t like, taste bad and is super sticky but will only trap insects not lizards or mammals. It is water resistant. I have had success with it on fruit trees and am now trying in on polyvinyl irrigation lines to keep them from chewing through.

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  13. Pam Peirce

    I hope the tanglefoot works! Rats eat just about anything. (I think they don’t like peppermint.) I still think to make a dent in the rat population, a community has to work together to clean up brush and not leave birdseed on the ground, or cat food around outdoors and thus remove cover and food for rats. Owl boxes might help as well.

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  14. Rick

    This year, 2018, I had rats eating my oranges on the tree. The problem is that no bait will attract them when they are safe eating the insides out while on the tree. I picked all the oranges and then put out traps with orange and another with costco rosemary parmesan bread. I got one, but there is still one out there that would not go for the bait in the traps no matter what it was – I watched with a motion triggered video camera. I’m going to design a rat trap that will go over an orange. They tend to come back to the same chewed up orange, I guess because they don’t have to chew through the skin. A few years ago the apricots were disappearing, so I set up the trail camera. It was a family oriented rat party with about 10 rats having a blast. They would not go for the bait, so I set a number of snap traps around the trunk and nailed several of them just randomly getting caught. Also, those rats can jump 3 feet high and jumped over the barrier I put on the trunk.

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  15. Grace

    Do the damaged branches where the bark has been eaten need to be protected or removed?

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  16. Pam Peirce

    Generally, remove dead branches or ones so badly damaged that they will die. If the bark is eaten all the way around a branch it will die, but it may die if it is severely damaged. If you can protect damaged branches (how? Wire mesh coverings would need rather small openings.), you can wait and see if they form callus and regrow some bark to cover the bare areas. In this case, remove any loose bark at the edges of the damage, as this will help with recovery. (We want to call it “healing” but tree people don’t call it that.)

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  17. Lucia

    Has anyone had a good response by planting peppermint? Does it really work? We don;t want to put poison because our neighbors have cats that come and visit us but our lime tree is taking a beating. It almost feels as if the shelter in place made the problem worst. Our orange and lime tree are against a fence and it’s clear that they come by walking on the fence because branches are clearly broken close to the fence.
    Any other suggestion ??
    Thanks!!

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