A “plague” of rats has cultivated concerns in the agricultural sectors of northwest Costa Rica, causing the government to declare a state of emergency Monday.

The problem is focused in Guanacaste, the central Pacific and the region north of Puntarenas, according to a statement from the Agriculture and Livestock Ministry. It mostly affects the production of sugarcane, rice and corn, while pineapple farms have also faced damages.

It is not so much a plague as an infestation of Central American “country rats” that eat through the stalk of plants and ruin harvests, said Luis Sánchez with the Agriculture and Livestock Ministry.

“It's a very common species in the Central American region,” Sánchez said. “They attack the base of the plants.”

While the invasion has steadily grown in magnitude for four straight years, this year has been the worst so far, due to the unusually dry conditions which have already left many farmers pulling in smaller yields, Sánchez said. The emergency was declared, he said, so that farmers in affected areas can coordinate with the Plant Health Department in eradicating the rats.

“We already have a control campaign,” which began collecting information on the problem in Nov. 2008, Sánchez said. “We are already working in a number of areas, and we are expanding our work.”

The Plant Health Department is responsible for dealing with the rats. They will use anti-rodent baits, along with the massive use of rodent traps, according to the statement.