Pine needle scale is a pest that is predominately found on Scotch and Mugho pine. You can identify this pest by looking for a 1/8-inch long white scale cover. These scale covers are long and narrow in the front (oyster shaped) becoming broader as you move down the scale. You will find 1-30 purplish coloured eggs underneath this scale cover. If you find adults underneath the scale they will be reddish to reddish brown in colouration.
The eggs begin hatching in mid May and once again in mid July. The hatching time period is short and occurs in 7-10 days. The first hatching in mid May will predominately attack the older needles, as your new growth has not yet fully developed. The second hatching in mid to late July will attack the current or new growth. Because pine needle scale is able to produce 2 generations per year, they are able to create a rapid buildup of population.
You will see little or no damage until the pine needle scale has a chance to build up its population. This usually takes one to two seasons. A pine needle scale infestation will generally not kill a healthy mature tree, but does result in stunted growth, or a general state of decline. Because of this weakened state, the tree is more susceptible to other problems such as drought, insects etc.
CONTROLLING THE PROBLEM:
By using Integrated Pest Management you can evaluate at which point you should introduce a chemical control. Small populations of scale usually do not create a problem for healthy trees. When you observe 10-15 scales per needle it may be time to incorporate chemical control. Lady bugs and parasitic wasps do a fine job of controlling scale populations. If you are using dormant oil to control pine needle scale, ensure you follow all directions carefully. Apply the dormant oil after most of the eggs have hatched. Re-apply once the second hatching occurs.