http://hoosiermushrooms.org/index.php?/activities/hms-online-forays-2019/

Please ensure that any specimens you collected are fully dry before putting them in a ziplock bag. If they have any moisture left in them, they will mold once they are in the bag and will be of no lasting value.

A dehydrator is the simplest method for drying. If you have an adjustable thermostat, dry them at the lowest setting.