Tree Health in Colorado
A comprehensive state guide for Colorado is coming soon. Below are current tree health alerts tracked for this state.
View all Colorado alertsCurrent Threats in Colorado
Emerald Ash Borer
INSECTAn 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.
Mountain Pine Beetle
INSECTA native bark beetle responsible for massive die-offs of lodgepole, ponderosa, and whitebark pines across western North America. Climate change has expanded its range northward and to higher elevations. Outbreaks have affected tens of millions of acres.
Ips Bark Beetles
INSECTA genus of bark beetles that attack stressed and weakened pines throughout North America. While they typically colonize dying trees, drought and overcrowding can trigger outbreaks that kill healthy timber.
Dutch Elm Disease
DISEASEA 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.
Powdery Mildew
FUNGUSA 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.
Thousand Cankers Disease
DISEASEA disease complex involving the walnut twig beetle and an associated fungus that has caused significant mortality of black walnut, particularly in western states. Thousands of small cankers coalesce to girdle branches and the trunk.
Dothistroma Needle Blight
FUNGUSA fungal disease of pines that causes premature needle loss and can significantly reduce growth and vigor. It affects many pine species but is especially damaging to Austrian, ponderosa, and Monterey pines. It has increased in severity with climate change.
Rhizosphaera Needlecast
FUNGUSA 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.
Stigmina/SNEED Needlecast
FUNGUSA fungal disease of spruce very similar in appearance to Rhizosphaera needlecast but caused by a different fungus. Often occurs alongside Rhizosphaera. It has become increasingly recognized as a major cause of spruce needle loss, particularly on Colorado blue spruce. Diagnosis requires microscopic examination to distinguish from Rhizosphaera.
Cytospora Canker
FUNGUSA common fungal disease of spruce and other conifers that causes branch dieback, typically starting from the lowest branches and progressing upward. Colorado blue spruce and Norway spruce are especially susceptible. The fungus enters through wounds or stressed tissue. White resin bleeding on bark is a hallmark sign. Stressed trees are most vulnerable.
Verticillium Wilt
FUNGUSA soilborne fungal disease that affects hundreds of plant species including maples, elms, redbuds, and many other trees. The fungus invades through roots and colonizes the vascular system, blocking water transport. Symptoms often appear suddenly on individual branches. Maples are particularly susceptible. Olive-green to brown streaking in the sapwood is diagnostic.
Bronze Birch Borer
INSECTA 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.
Leaf Spot Diseases
FUNGUSA broad group of fungal diseases that cause discrete spots on the leaves of deciduous trees. Most are primarily cosmetic and do not seriously harm established trees. They are most common during wet spring and summer weather. Many different fungi cause leaf spots on different tree species.
Seven-spotted Lady Beetle
INSECTThis is a picture of a Coccinella septempunctata at Fort Armistead Park in Baltimore City, Maryland.
Asian Lady Beetle
INSECTFound alive but in terrible shape. Was swimming around in the water bowl we put out for feral cats here. Also appeared to have had a run in with a spider web, as it had something stuck all over it. Got a lot of suggestions for fungi and parasitoids that target ladybeetles, so maybe its appearance is more a function of a disease or parasite process taking place. It was definitely having trouble getting adound, but could be due to having been in the water for a long time and/or having bits of web
LeConte's Giant Lady Beetle
INSECTLeConte's Giant Lady Beetle observed in the wild. Research-grade iNaturalist observation.
Red Admiral
INSECTSeemed to be warming its wings in a patch of sun in the middle of the sidewalk, where I accidentally disturbed it while walking by. It landed on me and hung out for a little bit before I encouraged it to disembark, and it continued on with its business.
White-lined Sphinx
INSECTExtremely friendly breezeway light visitor. I attempted to deposit it on nearby common evening primrose but it followed me back inside. Audio is the moth's wings.
Painted Lady
INSECTSeveral days of hot record setting weather in Jefferson County. Co. Painted Ladies are in flight at the base of North Table Mountain. This butterfly was much larger than most of what I've seen here...in past two days. Migrating or overwintering?
Mourning Cloak
INSECTMourning Cloak observed in the wild. Research-grade iNaturalist observation.