I have had four mugo pines for many years. There is a white blight on the needles. One plant became infected and I ignored it and it effectively killed the plant. The blight has now moved from that plant to one adjacent (see photo). My other two pines are metres away and healthy. What is this and is it treatable? What do you recommend doing with the infected plants?
I think that what your mugo pine (Pinus mugo) has is pine needle scale (Chionaspis pinifolia), a small armored insect that feeds on the sugars in the needles of pine, spruce and fir trees. Pine needle scales look like oyster shells or white blisters on the needles. They are a serious pest that often kills the infested needles and even the whole tree.
Pinus mugo is a shrubby pine introduced into North America from Europe and along with another introduced species, Scots pine (Pinus sylvestris) is more frequently damaged by scale than native pines.
The scale may not have completely infested your second pine. You may be able to control the infestation by pruning out the affected branches. You could also use dormant oil spray next spring – in late March or early April, before new growth begins. The dormant oil coats the scales, suffocating them, but it is nontoxic to humans, birds, and pets.
If however, it looks as if the second pine is succumbing to the scale, it may be best to remove the infested tree and hope that the remaining two trees will survive.
For more information on mugo pines and pine needle scale, see: