When should an ash (green and white ash) be pruned?

Carmel Urban Forestry publishes an approved species list (last revised 3/28/2024) whose "Undesirable Trees" section reads like a field guide to what fills older Hamilton County streets: silver maple (shallow roots, weak wood), Callery pear, pin oak, red maple and all Fraxinus for emerald ash borer. Approved large street trees run to swamp white oak, bur oak, chinkapin oak, hackberry, male-only ginkgo, thornless honeylocust, Kentucky coffeetree, baldcypress and London planetree; note Callery pear is discouraged locally but is not yet banned in Indiana — 312 IAC 18-3-25 currently lists 44 species without it. That context matters for ash (green and white ash): emerald ash borer has been confirmed in all 92 indiana counties since 2017, so the question on a central indiana ash is almost never whether to save it — the untreated ones are already dead or dying and only trees on an active systemic treatment program are still viable. Removing an ash (green and white ash) around Carmel runs roughly $400–$1,900, and in Village of WestClay, Brookshire and Woodland Springs access is usually what decides where in that range you land.