Summer Tree Damage
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Extension News
There are two fairly noticeable tree damage problems in western North Carolina (WNC) here in the middle of summer. Before I go any further, both of these problems are not serious threats to the health of the trees affected. One is damaged caused by the periodical cicada that was present in great numbers in some parts of WNC earlier this spring. The other problem is the black locust trees turning brown early, due to a common native insect.
Let’s look at the cicada damage first. Periodical cicadas emerge in May or June, either on 13 or 17-year cycles. Male cicadas make a loud buzzing sound (to attract females) that is synchronized to make a deafening noise. After mating, females slice open the bark of small twigs and insert eggs in two rows. The most obvious damage is that caused by this egg laying process in small twigs. This damage causes twigs to split, wither, and die, causing a symptom called "flagging." It’s usually the tips of branches that are affected.
Flagging is especially serious on young plants (four years or younger) because more of the branches are of the preferred small size for laying eggs. Large, established trees can withstand considerable flagging. Some of the more favored trees for egg laying include maple, oak, hickory, beech, ash, dogwood, magnolia, willow, apple, peach, cherry and pear. Flowers, vines and shrubs include: Rose of Sharon, rose, raspberry, grape, black-eyed Susan, hollies, rhododendron, viburnum, junipers, and arborvitae. More than 270 species of plants have been noted as hosts for egg laying female cicadas.
Here’s an interesting fact: One to several dozen eggs can be laid in one branch, with up to 400 eggs being laid by each female in 40 to 50 sites. That’s a lot of damage to small twigs!
Cicada eggs remain in the twigs for six to ten weeks before hatching. The newly hatched, ant-like nymphs fall to the ground where they burrow 6 to 18 inches underground to feed for the next 13 to 17 years.
The second problem is black locust trees turning brown in the middle of the summer. The cause of this dramatic looking damage is an insect called the locust leafminer. Immature and adult leafminers feed on black locust leaves and the result of all that feeding is brown locust leaves in July. Some locust trees respond by putting on some new leaves, while others may go dormant early. Either way, most every tree affected by this insect will be back growing well next spring.
So, if you see the tips of some branches turning brown, this is probably damage from the periodical cicada. These branch tips will eventually fall off and the trees will not suffer any lasting health effects from this damage. If you notice black locust trees turning brown in the middle of the summer, it’s just the annual locust leafminer feeding frenzy. Don’t worry too much about either of these problems. Both of these outbreaks are more spectacular than destructive.
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Jeffrey E. Seiler
County Extension Director - Jackson/Swain Counties
N.C. Cooperative Extension - NC State University
Jackson (828) 586-4009
http://jackson.ces.ncsu.edu
Swain (828) 488-3848
http://swain.ces.ncsu.edu