Observatree volunteer activity from the start of the project (July 2014) to the end of July 2017

Number of hours recorded: 12,483

Number of tree health site surveys completed: 2675

Number of Tree Alert reports verified: 52

Priority pest and disease findings:

  • Oriental chestnut gall wasp
  • Chalara dieback of ash
  • Acute oak decline
  • Dothistroma needle blight
  • Horse chestnut leaf miner
  • Oak processionary moth
  • Great spruce bark beetle
  • Sirococcus tsugae
  • European Mountain Ash Ringspot Associated Virus (EMARAV)
  • Phytophthora lateralis

Other key findings:

  • Dutch elm disease
  • Perenniporia
  • Armillaria
  • Cristulariella depraedans
  • Coral spot
  • Daldinia concentrica
  • Guignardia leaf blotch
  • Oak powdery mildew
  • Phytophthora alni
  • Phytophthora cinnamomi


  • New sentinel trees survey launched
  • New findings of OPM, Sirococcus and EMARAV
  • Volunteer David Griffith has identified ash trees infected with Chalara dieback of ash in over 20 new 10km grid squares, completed 68 Tree Alert reports and logged nearly 365 volunteer hours
  • Volunteers asked by Defra to check sweet chestnuts for signs of chestnut blight

Tree Alert activity between April 2015 and September 2017

Tree Alert enquiries by country (572 total) 

Top 5 host tree species (in order):

  • Ash
  • Oak
  • Sweet chestnut
  • Cedar
  • Plane
Top pathogen reported: Chalara OLYMPUS DIGITAL CAMERA Top pest reported: Oak processionary moth Oak Processionary Moth - Credit Forestry Commission