the fungus enters the leaves and spreads to the branches
the disease has a complex life history and cannot spread directly from pine to pine but must develop on an intermediate host: the leaves of Gooseberries or Currants (Ribes spp.)
the fungus seems to have little impact on Gooseberries or Currants
Impact on Trees
seedlings are most vulnerable and usually killed
older trees can have branches or tops killed by the fungus but will survive as long as the trunk is uninfected
tree is killed when the infection girdles the trunk
What can be done to control this tree killer?
past efforts involved removing the intermediate host (Gooseberries and Currants) or preventing them from being grown in important pine-growing regions
preventing the shipping of pine nursery stock from infected to disease-free areas
pruning lower branches to reduce the likelihood of infection migrating to the trunk
developing disease-resistant strains for replanting