How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

The roof rat, sometimes called the black rat, is a common vertebrate pest in citrus orchards. It builds leaf and twig nests in citrus trees or nearby trees or it can nest, in debris piles or thick mulch on the ground. This agile, sleek rat has a pointed muzzle and tail that is longer than the body and head combined.

Be sure to identify the species of rat present to avoid killing nontarget or protected species.

Be aware that endangered native kangaroo rats (Dipodomys spp.) and the riparian woodrat (Neotoma fuscipes riparia) resemble pest rats, but are protected by law. Unlike the hairless, scale-covered tail of roof rats, the tails of kangaroo rats and the riparian woodrat are covered with fur. The riparian woodrat is active mostly during the day, and its tail is somewhat shorter than the combined length of its body and head. A kangaroo rat's tail is noticeably longer than its body and head combined. Kangaroo rats are nocturnal, but unlike Norway rats and roof rats, which move on all four legs, kangaroo rats hold their front legs off the ground and travel by hopping on their hind legs.

DAMAGE

Rats gnaw on electrical wires, wooden structures, and fruit on trees. After harvest, they damage fruit in bins by chewing it and leaving excrement. Rats are active throughout the year, and mostly at night.

MANAGEMENT

Reduce shelter and nesting sites of rats. Eliminate debris and wood piles. Store materials neatly and off the ground. Thin and separate non-crop vegetation around orchards where feasible.

Baits and rat-sized snap traps placed in trees are the most effective control measures. 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 sweet fruit or nut meats, but do not set the traps until after bait is readily eaten. Secure anticoagulant wax blocks in a bait station before placing in trees on limbs 6 feet or more above the ground. Placing the wax blocks in a bait station will prevent chunks of the anticoagulent wax from dropping to the ground and creating a hazard.

Be aware that certain types of single-dose rat baits for use inside buildings are not labeled for use outdoors in orchards; these are hazardous to wildlife and should not be used.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Vertebrates
M. W. Freeman, UC Cooperative Extension Fresno County
R. E. Marsh (emeritus), Wildlife, Fish and Conservation Biology, UC Davis
T. P. Salmon, UC Cooperative Extension, San Diego County

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