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U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Native Forest Insects and Diseases

Native Forest Insects

Tens of thousands of species of insects are found in our forests and rangelands, and many play an important role in pollinating plants, recycling nutrients, decomposing vegetation, and providing food for wildlife. They also occasionally can kill trees and impact forest health. Forest Health Protection surveys our forests to detect insect outbreaks, provides assistance to land managers to manage pests and develops tools for detection and management. Several native species, such as the southern pine beetle, several species of western bark beetles (mountain pine beetle, spruce beetle and Douglas-fir beetle), and spruce budworms have had significant impacts on forests across the US.

  • Southern Pine Beetle
  • Western Bark Beetles
  • Spruce Budworms

Learn more about native forest insects


Native Forest Pathogens

Forest pathogens are often microscopic organisms that attack trees in ways that can be hard to see with the naked eye. Tree pathogens such as fungi, bacteria, phytoplasmas, virus, viroids, and higher parasitic plants can serve as disease agents and are normally considered part of a healthy forest. However, under favorable environmental conditions and presence of a susceptive host they can do significant damage to forest resources nationwide. One good definition for tree disease is any harmful deviation, caused by a persistent agent, impacting the normal functions of the tree. There are roughly five common tree problems highlighting the importance of pathogens in the forest. They include Wilts, Cankers, Rusts, Mistletoes, and Root Disease. Symptoms generated by their persistence can be identified on leaves, branches, trunks, or roots expressed as blights, galls, leaf spots, or witches brooms. Understanding the critical control points of their disease cycles is key to successful management.

  • Sycamore Anthracnose
  • Armillaria Root Rot
  • Swiss Needle Cast

Learn more about native forest pathogens


Abiotic Forest Damage

Just as trees can be damaged by infectious microbes such as fungi, bacteria, viruses, nematodes, and higher parasitic plants, they can also be damaged by noninfectious factors causing problems referred to collectively as "abiotic diseases" or "abiotic disorders". Drought, nutrient deficiency, winter burn, unfavorable soil properties (pH), fertility imbalances, moisture extremes, temperature extremes, chemical toxicity, and other problems are examples of abiotic disorders that can reduce vigor and if prolonged long enough, kill trees. Many of these abiotic disorders can predispose plants to diseases caused by infectious microbes. It is important to recognize that many ‘biotic’ tree diseases can have the same symptom signatures as ‘abiotic’, therefore careful diagnosis is necessary to determine the actual cause of the tree disease.

  • Drought
  • Nutrient Deficiency
  • Winter Burn

Learn more about abiotic forest damage

Southern pine beetle damage

Southern pine beetle damage on the Snoopy Plantation, Indian Mounds Wilderness Field. Photo by Ronald F. Billings, Texas A&M Forest Service.