Rats in Fruit Trees

Hollowed out oranges, papaya, bananas and other fruits, whether hanging on the tree or on the ground, are definitely signs of rat feeding.  In Hawaii, there are four rodents that cause economic hardship: the roof or black rat, the Norway or brown rat, the Polynesian or Hawaiian rat, and the house or field mouse. In addition, they are carriers of contagious diseases including plague, murine typhus, leptospirosis, and salmonellosis. Today, most notably, they are part of the disease cycle known as Rat-Lungworm. See health.hawaii.gov/docd/disease_listing/rat-lungworm-angiostrongyliasis/  for more information and prevention of this serious condition.

Rodent control is not easy due to their ability to adapt to changes and their capacity to reproduce.

Rats are nocturnal. They have excellent memories and very repetitious habits. They are easily frightened of new things placed in their environment. The roof rat is most pronounced in this tendency. Rats have a keen sense of smell and hearing, and only a fair sense of sight with the ability to see in the dark.

Besides the hollowed out fruits, other common signs of rats are droppings, rubmarks, gnawings, nests, and unpleasant odors.  

                                                         Rat Damage on Oranges - UC IPM

In controlling these pests around the home, the first step is to clean up the environment by removing accesses to food and shelter. Physical barriers such as screens may need to be installed. When only a few rats are involved, trapping can be successful, both live and snap traps. Devices that kill rats by electrocution (e.g., Rat Zapper or Victor Electronic traps) are expensive but effective.

Paraffin-type bait blocks containing anticoagulants are also effective in controlling rats. They appeal to the rats gnawing instinct, especially those blocks with numerous ridges. Baits should be replaced immediately as they are eaten, since a single feeding on the first generation anticoagulants such as diphacinone, will not control rats; multiple doses over several successive days is required. The newer “second-generation” compounds such as brodifacoum, bromadiolone, difenacoum, and difethialone, which can be fatal after a single feeding. Prepackaged, ready-to-use bait stations containing some of these toxicants can be purchased by homeowners. 
   

Some poisons have a secondary effect which will affect animals that consume dead or nearly dead rodents. Thus, it is imperative that strict safety precautions be used in the placement and disposal of poison baits for rodents.

For more information on rats see the UC IPM website, http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74106.html