Members of the Maine timber industry are pushing back at a proposal to prohibit aerial spraying of herbicides in the state’s forests. Herbicides are substances that destroy unwanted vegetation. They are used widely in agriculture, forestry and other industries. A bill proposed by Democratic Senate President Troy Jackson stated that it would ban the use of “aerial herbicide spraying for the purpose of deforestation.” Jackson’s proposal was scheduled Thursday to come before a legislative committee on agriculture, conservation and forestry. Several members of the timber industry have said the bill’s definition is far too broad, and enacting the proposal would take a valuable tool away from companies that harvest trees from Maine’s vast forests.