Rhode Island

A devastating vascular wilt disease spread by elm bark beetles that has killed millions of American elms since the 1930s. The fungus blocks water-conducting vessels, causing rapid wilting. It fundamentally changed the American urban landscape.

Affecting 45 regions

A fungal disease that functionally eliminated the American chestnut as a canopy tree species in eastern forests by the mid-20th century. Once numbering in the billions, mature American chestnuts are now exceedingly rare. Root sprouts survive but are re-infected.

Affecting 25 regions

A bacterial disease that primarily affects members of the rose family, including apple and pear trees. It can destroy entire orchards in a single season. Bacteria spread rapidly during warm, wet spring weather through blossoms and wounds.

Affecting 32 regions

An emerging disease caused by a foliar nematode first identified in Ohio in 2012. It has spread rapidly through the native range of American beech. Affected trees can decline and die within 6-10 years. No effective treatment exists at scale.

Affecting 12 regions

A common fungal disease of spruce trees, especially Colorado blue spruce, throughout the Midwest and Northeast. The fungus infects current-year needles through stomata, causing them to turn purple-brown and drop prematurely. Inner and lower branches are affected first because humidity is higher there, and the disease progresses upward and outward over successive years. Severely affected trees may retain only the current year's needles at branch tips.

Affecting 25 regions

A native North American wood-boring beetle that attacks birch trees, especially paper birch and European white birch in landscape settings. Larvae feed under the bark in a serpentine pattern, disrupting nutrient and water transport. Dieback starts at the top of the crown and progresses downward, the opposite pattern of many other pests.

Affecting 26 regions

An invasive wood-boring beetle native to Asia that has killed hundreds of millions of ash trees across North America since its discovery in Michigan in 2002. Larvae feed on the inner bark, disrupting nutrient and water transport.

Affecting 36 regions

An invasive planthopper native to China first detected in Pennsylvania in 2014. While it primarily threatens agriculture (grapes, hops, fruit trees), it feeds on over 70 plant species. It excretes honeydew that promotes sooty mold growth.

Affecting 21 regions

A tiny aphid-like insect native to Asia that feeds on hemlock sap at the base of needles. It has devastated eastern hemlock populations from Georgia to Maine. Trees typically die within 4-10 years of infestation.

Affecting 20 regions

An invasive moth introduced to Massachusetts in 1869. Caterpillars defoliate hundreds of tree species, preferring oaks. Repeated defoliation weakens and can kill trees, especially when combined with drought stress.

Affecting 20 regions

An invasive beetle introduced to New Jersey in 1916. Adults skeletonize leaves of over 300 plant species while larvae (grubs) damage turf grass roots. They are particularly damaging to linden, birch, and fruit trees.

Affecting 35 regions

A fungal disease requiring two hosts to complete its life cycle: eastern red cedar (juniper) and apple or crabapple trees. It causes economic losses in apple orchards and aesthetic damage to landscape cedars.

Affecting 34 regions

A group of fungal diseases causing leaf spots, cankers, and shoot blight on many shade trees. Sycamore, dogwood, maple, and oak are commonly affected. Cool, wet spring weather promotes infection of newly expanding leaves.

Affecting 38 regions

The most economically important disease of apples worldwide. The fungus overwinters in fallen leaf litter and releases spores during spring rains. Severe infections reduce fruit quality and yield and can defoliate trees by mid-summer.

Affecting 26 regions

Asian Longhorned Beetle Damages hardwood trees by tunneling deep into trunks and branches - identified by USDA APHIS as a pest threat.

Affecting 50 regions

A widespread group of fungal diseases that produce a distinctive white powdery coating on leaves and shoots. It affects hundreds of tree, shrub, and plant species. Unlike most fungi, it thrives in warm, dry conditions with high humidity.

Affecting 49 regions

A very common and distinctive fungal disease of maple leaves. The raised black spots are dramatic in appearance but the disease is almost entirely cosmetic and does not harm tree health. It is most severe in cool, wet years. The fungus overwinters in fallen leaves.

Affecting 22 regions