It was truly a tree-mendous mystery.
Troubled trees that have been found throughout the Cape and Islands over the last few years have only recently been diagnosed.
The symptoms are cause for great concern. Some of our native and ubiquitous black oaks are not fully leafing out, leafed-out trees are sporting brown foliage in the summer, and twigs are appearing swollen with small pin-sized holes — all reasons to sound the alarm.
If you are seeing any of these indicators in your black oak trees you, too, might have an infestation.
Cynipid gall wasps are likely the culprit. While there are hundreds of types of gall wasps, only a few members of this group have been identified as the responsible parties in the latest outbreak. Both Bassettia ceropteroides and Callirhytis ceropteroid have been fingered as the enemy, though most arborists agree that the former, also called the crypt gall wasp, is the one to be most worried about.
Crypt gall wasps lay their eggs in the tree’s twigs. As a gall (swelling) forms to provide for the insect larvae’s growth, the vascular system of the tree becomes disrupted. The effects are similar to girdling, where water and nutrients are unable to reach the outer branches and twigs, robbing them of the resources they need to survive.
Just recently this pest has become a problem here. Though some reports say that the crypt wasp has been causing damage on the Island since 2009, it was definitively confirmed just last year. Both Cape Cod and Martha’s Vineyard are seeing a substantial outbreak.
The damage wrought by the crypt gall wasp can go from bad to worse. Some trees have a limited infestation while others lose more than 90 per cent of their leaves, looking as bare and naked as they do in the heart of winter. While die-off can take a few years, the damage can be quite visible. The additional stress can also cause epicormic growth, which is when new shoots grow from the trunk or large limbs of the tree.
It is the most vulnerable trees that get hit the hardest. With the spate of hurricanes over the last few years, many of the coastal trees became damaged by salt spray. The winter moths have also been an added stress, weakening trees over the last few years. It is when the trees are in this susceptible state that the most damage can be done by this native pest.
You can help affected trees by bucking up their defenses. Don’t let drought weaken them. Water well if you think you have a crypt gall wasp infestation. Also, improving soil fertility to damaged trees can give them a boost. Some arborists offer injection treatments, though the jury is still out on their effectiveness.
The black oak’s battle seems to be continuing this season. However, the scourge of the crypt gall wasp is known for its boom and bust cycle. An infestation in Long Island in the 1990s, for example, subsided before scientists and arborists could study treatment options. For the sake of the trees, and us tree huggers, let’s hope that the wasps are beyond the boom and are heading for a big bust.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.