LANSING, Mich. — State officials have revised a quarantine of some walnut products intended to protect Michigan trees from a fatal disease.

The Michigan Department of Agriculture and Rural Development is trying to ward off an outbreak of thousand cankers disease, which has killed numerous walnut trees in the western U.S.

The quarantine generally prohibits shipment of walnut nursery stock, certain walnut timber products and hardwood firewood into Michigan from infested states.

Walnut furniture, veneer, kiln-dried walnut lumber without bark and walnut nuts and nutmeats are exempt.

Michigan’s quarantine first was implemented in 2010. The revisions reflect updated information about where else the disease has been found in North America.

Additional information is available online .