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Plant Pests and Pathogens

Plant Pests and Pathogens

Peninsula Horticulture uses an integrated approach to managing insects and diseases that begins with maintaining plant health using sound cultural practices including pruning and creating optimal soil conditions for plant growth. Periodic inspections are essential to detect pest infestations before they reach damaging levels. Peninsula Horticulture's arborists are trained to recognize beneficial insects that will help naturally suppress pest populations, and we also release beneficial fungi and insects to augment existing populations. When treatments are necessary, Bartlett can apply organic and naturally based materials and reduced-risk products that provide effective pest suppression while protecting people and the environment.


Hundreds of insect species damage leaves, stems, and branches; roots; and flowers and fruit of landscape plants. But not all insects on trees and shrubs are damaging. Some are beneficial and may help pollinate flowers or could be predators or parasites on insects that damage plants. Peninsula Horticulture's arborists are trained to correctly identify these beneficial insects and mites and can devise effective management programs that protect landscape plants from serious damage while conserving beneficial organisms.
Top insect and arthropod pests that threaten or damage landscape plants on the West Coast:

  1. Oakworm
  2. Turpentine beetle
  3. Oak Bark beetle
  4. Bronze birch borer
  5. Ambrosia beetles
  6. Pysllids
  7. Whiteflies
  8. Spider mites
  9. Scale insects
  10. Thrips
  11. Weevils
  12. Adelgids


Diseases are abnormalities in trees and shrubs caused by microorganisms such as fungi and bacteria and by environmental stress such as drought, temperature extremes, and air pollution. Diseases are often difficult to diagnosis as different causal agents can produce similar symptoms. Accurate diagnosis is essential to developing effective treatment programs. Peninsula Horticulture operates a modern diagnostic laboratory to support pest management services to ensure accurate identification and treatment of plant problems. Top diseases that threaten or damage landscape plants on the West Coast:

  1. Sudden oak death
  2. Phytophthora root rot
  3. Armillaria 
  4. 1000 Cankers disease
  5. Dutch elm disease
  6. Fireblight
  7. Anthracnose
  8. Leafspot diseases
  9. Wood decay
  10. Cankers
  11. Verticillium wilt
  12. Nutrient deficiencies
  13. Drought
  14. Powdery mildew