Disappearing Tomatoes

Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County 

Client's Request (from telephone conversation):  Help!... I'm growing tomatoes in an enclosed courtyard. I'm now seeing tomatoes disappearing and some with gnawed portions of low hanging tomatoes. I've heard a lot about voles being quite prevalent this year. Do you think it is voles? Other than the disappearing tomatoes and gnawing, I haven't really seen signs of other “animals”.

MGCC Help Desk Response: Thank you for calling the UC Master Gardener Program Help Desk this morning with your question about your disappearing tomatoes.

Although you suspect voles in your courtyard, they are an unlikely culprit in this case because the garden area you described is entirely enclosed except for the roof area, which is open to the sky. In order to enter the garden area, an animal would need to climb, and voles are poor climbers. It is true that Contra Costa County has had an explosion in the vole population this year, but nevertheless it does not seem likely that they are your culprit.

On the other hand, rats are excellent climbers and though somewhat larger, look similar to voles. (Voles can be up to 8 inches long, including the tail, and they have a short tail. While rats are much larger than the common house mouse or meadow vole, a young rat is occasionally confused with a mouse. In general, very young rats have large heads and feet in proportion to their bodies, whereas those of adult mice are proportionately much smaller).

Rats are very common in most neighborhoods. There are two common types of rats: Norway rats (Rattus norvegicus) and roof rats (Rattus rattus). Both are active at night. Either one could be eating your tomatoes, although roof rats are the more likely culprit, since they favor fruits. Rats could be entering your courtyard garden from the roof top opening, or they could already be resident in your attic or building.

Reducing the rat population should be the first step in protecting your tomatoes. Sanitation and making your courtyard less hospitable to rats, can go a long way to reducing the population. If you have bird feeders, either remove them or clean under them daily and take them inside at night. Also, talk with your neighbors about reducing rat habitat, as this is usually a neighborhood-wide problem. (Rat habitat outside of your courtyard might include woodpiles, moist areas in and around gardens, and dense vegetation such as ivy.)

Trapping can also work to reduce the population, but it is difficult to make a permanent dent in the population through trapping alone. Snap traps are the best traps to use as long as you can place them where other animals (squirrels, opossums, and birds as well as your dog or neighbors' cats) can't get to them. For roof rats, the traps should be placed in off-the-ground locations such as branches or fences.

If you use traps, check them frequently for dead rats. Do not touch rodents with your bare hands. Make sure you wash your hands thoroughly after handling traps. Dispose of dead rats by burying them or by placing them in a sealed plastic bag and putting them in the trash.

In the meantime, physical barriers can be used to protect your tomato plants directly. One approach is to erect a 1 foot tall barrier using metal roof flashing (obtainable at the hardware store) all the way around the planting bed. Rats are unable to gain traction on the slippery surface. Alternatively, you could build a small-mesh (no larger than 1/4 inch holes) enclosure around the bed or around each plant. Since rats, especially roof rats, are excellent climbers, the wire mesh enclosure would need to go up the sides and across the top of the plants.

We do not recommend use of rat poisons, especially out of doors, due to risk of harm to wildlife and pets either by eating the poison directly and/or indirectly in eating the rat.

For more information on rat identification and management, see: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74106.html

And for information on voles see: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7439.html

Hope this information helps you eliminate those disappearing tomatoes. From the inquiries Master Gardeners have received about rats this year you are not alone.

Please let us know if you have further questions.

Good luck with your tomatoes!

Help Desk of the UC Master Gardener Program of Contra Costa County (MCW)
Please Join us at "Fall for Plants" on September 9 for the workshops and the plant sale, Registration is optional, but it'll get you a free plant from the sale. Hope to see you there.

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Note: The  UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925)646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/).