Fraxinus pennsylvanica, green ash, is the most widely distributed native ash in North America, ranging from the Atlantic coast to the Rocky Mountains and from southern Canada into Texas and Florida — a natural floodplain and bottomland species so tolerant of wet soil, compaction, heat, cold, and urban stress that it became one of the most heavily planted street and yard trees in the country through the mid-to-late 20th century, often as a direct replacement for American elms lost to Dutch elm disease. That sheer adaptability, combined with how extensively it was planted, made its losses to emerald ash borer especially visible and severe.
The emerald ash borer (Agrilus planipennis), an invasive Asian beetle first found in Michigan in 2002, has killed green ash across nearly its entire planted and native range, and the species is now classified as Critically Endangered by the IUCN — a stunning reversal for what was, within living memory, one of the most common trees in American towns and cities. A healthy tree can decline from first infestation to dead within 3–5 years. As with the other North American ash species, planting green ash today makes sense only alongside a genuine, ongoing commitment to systemic insecticide treatment wherever EAB is present, or in the shrinking number of areas the borer hasn't yet reached.
Verticillium Wilt
Lower leaves yellow and wilt, often on one side of the plant, with brown streaking in the stem and crown tissue when cut open. Plants are stunted and decline over the season.
Remove and destroy affected plants. Avoid planting in soil that has grown infected tomatoes, peppers, or other susceptible crops. Rotate beds and improve drainage; there is no cure once a plant is infected.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.
Emerald Ash Borer
Agrilus planipennis →Larval tunneling under the bark girdles the tree's phloem, cutting off nutrient transport; causes canopy dieback progressing from the top down, bark splitting, and death of the majority of untreated ash within 3–5 years of first infestation.
Systemic insecticide trunk injection (emamectin benzoate) by a certified arborist, repeated on a 1–2 year cycle, for trees caught early enough to be worth saving. Biological control via released parasitoid wasps (Tetrastichus planipennisi, Oobius agrili, Spathius spp.) is underway in many states as a longer-term population suppression strategy, not a rescue option for individual trees.