Flagging and needle drop are common occurrences with evergreens, and most often it’s due to a natural process and not disease. All evergreens, and some broad leaf plants, shed old foliage at some point every year.
Generally, it’s good to keep an eye on when trees naturally lose needles during the year. If flagging or shedding happens outside of the normal season, or if the tree is shedding its new needles, then it might be time to take some action.
Symptoms of Pine Tree Flagging and Needle Drop
Evergreens shed old needles due to both environmental stresses and natural ones. Most needles last around three years. Douglas fir and juniper needles last for 10 years or more. Bristlecone pines can keep their needles for as many as 30 years.
The symptoms of flagging start when brown foliage is observed, usually in late summer. These brown spots, called flags, generally continue into mid-fall. The affected parts are usually growth from previous years. Current year growth can be seen at the tips of branches and should stay green.
The flags are usually spread in a uniform manner throughout the tree. Flagging eventually ends in needle drop and this usually happens due to wind and rain at the end of the season. By spring, the tree will usually appear green and healthy.
How to Manage Pine Tree Flagging
Pine tree flagging typically starts in warm weather and is dispersed throughout the tree. It’s possible to reduce flagging by increasing water to the tree and also by pruning off the browning areas. In particular, cedar trees have shallow roots, which means they need more water when it’s hot and when they grow in sandy soil.
As previously mentioned, most trees that display flagging will eventually recover, and especially if given more care during the flagging period. Needles that turn brown are usually the inner needles from the tree’s top branches to the lower ones.
Browning on the outer needles, branch death or needle thinning only on the lower branches is more likely to indicate some type of disease.
Diseases That Cause Unnatural Pine Tree Flagging
When needles on the lower half of the tree are thin or dead and they also have black specks and dried resin near the base, then this is likely the result of tip blight. This is a condition that can and needs to be treated with fungicide.
Another condition, which can’t be treated, is known as pine wilt disease. This is caused by the pine sawyer beetle spreading a microscopic worm throughout the tree. The tree will usually turn completely brown in the fall and quickly die.
If this is determined to be the cause, the tree should immediately be removed and burned before spring when the beetle becomes active again. This disease is extremely infectious to nearby trees.
A fungus known as dosthristroma needle blight is treatable disease which causes yellowing and browning on younger needles.
Though most flagging is natural and will reverse itself after proper watering and needle drop, the kind that appears out of season may be fungus or disease and should be treated as such by a knowledgeable arborist or tree care company.