Scotch pine problems

As a non-native tree species, Scotch pines are notorious for harboring hordes of pests that can move into the more desirable red (or Norway) pine. Accumulative stress from drought and winter injury has allowed pest populations to build up in Scotch pines in a number of areas. If sanitation practices are not particularly aggressive, these pests can get out of hand.

Potential pests include pine bark beetle, turpentine beetles, root collar weevils, Armillaria root rot and Diplodia tipblight all of which can affect red pine. All but Diplodia tipblight are considered secondary pests, normally associated with dead and dying trees. However, all can attack healthy trees under the right conditions. Where a number of these pests are active in the same stand, the following will help bring them under control:

  1. 1. Remove dead and dying trees (any with discolored crowns), preferably before April 1st when most insects emerge
  2. 2. Chip, burn or debark all woody debris >2" in diameter
  3. 3. Tightly cover fresh cut firewood so insects can neither enter nor exit the pile
  4. 4. On pines less than twenty feet tall, prune lower pine limbs up to increase airflow and soil temperatures ? this will help reduce both root weevils and needle casts.
  5. 5. Where feasible, prune out branches infected with Diplodia blight
  6. 6. Where pruning is not feasible, remove Scotch pine infected with Diplodia blight growing over desirable red pines.

Of course, the best control of Scotch pine problems is basal pruning, i.e. remove and destroy the whole tree and plant something meant to grow in Minnesota.