Common Mugo Pine Pests
The sawfly and the pine needle scale are the most common pests of mugo pines. The shoot tip moth can also cause damage to young mugo pines. The sawfly is a pest of all pine species; tree death is rare though it is possible. Similarly, the pine needle scale (Chionaspis pinifoliae) affects all species of pine and can kill a pine much more easily than can a sawfly. Shoot tip moths or pine tip moths feed on all pine species and can be fatal to pines after prolonged infestation.
Learning the tell-tale signs of damage caused by each of these insect species is the key to determining which species is attacking your pines. Sawflies feed only on the pine needles themselves, so damaged needles will appear straw-colored and will eventually defoliate. The pine needle scale also feeds on needles, but after a prolonged infestation, pine tree scale feeding damage will manifest itself in poor foliage and an overall frosted appearance of the entire tree (rather than only in the needles themselves, as is the case with sawfly damage). Of all of the insects discussed, the pine tip moth produces the most conspicuous damage, altering the growth of the entire tree to a more bush-like appearance.
Signs of Infestations
Spotting an infestation by one of these insects before they have a chance to cause any noticeable damage can go a long way in protecting tree health. Regularly inspect the pine's needles for larvae or adult insects and for the eggs of the insects, often only appearing as tiny spots, before they reach the larvae stage. Pine needle scale eggs, larvae and adults can be observed anywhere on the tree, not just on the needles. Like all other moths, the life cycle of pine tip moths consists of four stages: egg, larva, pupa and adult moth. All are easily visible on mugo pine trees, but note that only the larval stage of the pine tip moth causes damage to pine trees.
Control methods of course depend entirely on the specific species that is attacking your mugo pine. If European sawfly egg or larvae only infest one or a few branches on your mugo pine, simply prune away and discard those branches. Introduction of natural predators such as wasps and lady beetles are effective at controlling pine needle scale and pine tip moth populations, though not as effective for a sawfly infestation. Use of approved insecticides should be considered only as a last resort; if possible, use an insecticide that leaves natural predator populations intact.