With problems in selling trees come increased problems with pests. As trees keep getting larger and start growing into each other there is more opportunity for algae and other pest problems. These are related to the lack of air movement around the trees.
In a field I visited today there were actually 3 problems causing discoloration of the foliage -- algae, elongate hemlock scale, and a disease called Rosellinia.The fungus grows in the interior needles, causing them to shed. The fungus grows in mats and produces the fungal spores pictured here.
The remedy for Rosellinia fungus and algae is to improve the air movement by keeping weeds in check, butt pruning trees, and removing trees that are growing into each other.
You can also control algae from developing in the foliage that was produced last year by spraying right at or just after bud break with the copper based fungicide Kocide. For information on algae control check out past entries on algae.