AUGUSTA — The state is providing homeowners with a free opportunity this fall to dispose of old pesticides that may be stockpiled on their properties.

Required registration — the deadline for which is Sept. 28 — is now open, and gives owners of homes and family farms and greenhouses the opportunity to safely and legally get rid of pesticides that have become caked, frozen or otherwise unusable, including those that are banned in the state.

It’s not uncommon for new owners of older homes or farms in Maine to discover they have inherited hazardous waste in the form of pesticides, with old chemicals such as DDT, lead arsenate, 2,4,5-T and chlordane left behind in barns, basements or garages.

In a statement released by the agencies overseeing the event, officials said it’s critical for the protection of Maine residents, wildlife and environment that pesticides and similar chemicals “be dealt with properly and not tossed in the trash or down the drain where they can contaminate land and water resources, including drinking water.”

There will be four sites throughout the state where pre-registered participants will be able to bring their obsolete pesticides and dispose of them at no cost.

The collected chemicals will go to out-of-state disposal facilities licensed by the federal Environmental Protection Agency where they will be incinerated or reprocessed.

Due to safety and regulatory requirements, disposal “drop-ins” are not allowed, so registration by the Sept. 28 deadline is necessary. Registrants will be contacted several weeks prior to the drive to inform them of their collection date and location.

To register, get additional details or learn important information about the temporary storage and transportation of obsolete pesticides, go to http://www.thinkfirstspraylast.org or call Henry Jennings, executive director of the Maine Board of Pesticides Control, at 287-2731.

Through jointly sponsored disposal events — which are funded entirely through pesticide product registration fees — the state’s Board of Pesticide Control and the Department of Environmental Protection have kept about 90 tons of pesticides out of the waste stream since 1982, according to the statement.