Photo Barbara Knapp - Cicada damage on one of her trees
by Essie Burnworth and Barbara Knapp (MD-TACF)
Subject: Brood X Cicada Damage to American Chestnut
Keywords: cicada, insects
In early May 2004, enthusiastic volunteers and members of the Maryland Chapter of TACF were looking forward to another fruitful year of American chestnut nurture and a bountiful harvest of nuts in the fall. More than 4,000 American chestnuts had been collected from Sugarloaf Mountain in Dickerson in the fall of 2003. The newspapers were advising that the 17-year Brood X cicadas would be emerging soon, and many of us remembered past cycles of these large, noisy bugs with the red eyes. But we were not prepared for the quantity of insects that showed up nor for their chestnut preferences!
The cicadas emerge from the ground as nymphs, but soon shed their skin and become flying adults. The almost deafening noise is of male cicadas singing to attract a mate. After mating, the female flies to a thin branch and cuts a slit in the wood, where she lays her eggs. After about 6 weeks the eggs hatch, and the larvae drop to the ground, where they burrow down to the roots of a tree, to wait another 17 years. The females seek out the branches with new growth and the incipient buds for the following year, and the gouges they make in the twigs kill the leaves and flowers and weaken the twig enough so that it often breaks off.
The established American chestnut orchards at Sugarloaf Mountain were truly covered with cicadas, and no small branch, whether on a 2-year-old seedling or a mature sprout, was left undamaged. The high infestation was also evident at Barbara Knapp's Germantown orchard where the Montgomery County champion and several other nut-bearing American chestnuts are growing.
The Maryland Chapter volunteers bagged some flowers, but there were very few flowers on any of the chestnuts. Some people have speculated that the pre-emergent cicadas, drawing nourishment from the chestnut roots, weakened the trees so that there was significantly less flowering.
By late summer, lifeless branches hung with dead brown leaves on all the chestnuts. When harvest time came, we found that there were almost no burs with nuts on any of the trees, and many of the bagged flowers were dead because the damage had not been apparent at the time of bagging.
The infestations varied by location; ThorpeWood orchard in Thurmont had less damage than Sugarloaf Mountain.
Late in the summer, when we could see the holes and dead branches in the seedling orchard at East Field on Sugarloaf Mountain, we tried cutting off the damaged branch and covering the wound with tree dressing. In the spring of 2005, we observed that this step had not improved the survival of the seedling - some leafed out on lower branches and some seedlings were completely dead. Having removed the damaged central part did not seem to help survival.
There was some published speculation that all those little dead bodies on the ground provided a nitrogen burst, and the trees would thus get fertilized and be vigorous the next spring. However, this was not the case. Very few flowers appeared on any of these chestnuts in the spring of 2005, and the cicada damage persisted another year.
At the TACF Annual Meeting in October 2005, Greg Miller from Ohio said that in his experience it took three years to recover from a Brood X emergence cycle. This represents a serious setback in our breeding activities here in Maryland. The good news is that the next infestation is not until 2021!
SOLUTIONS
1. Most importantly, monitor cicada progress in your area. It would be best not to plant chestnuts in areas where cicadas are expected to attack that year, as per the last line of Essie and Barbara's article. Similiarly, a new PA-TACF orchard established at the Reineman wildlife sancturay was hit hard.
2. Cover smaller trees with bird netting to try and discourage cicadas from laying eggs on small trees. One doesn't need to cover their trees directly as the cicadas emerge. In fact, you may trap them in your netting if you do so. Females do not lay their eggs until about 5-10 days after emergence, so give them some time to get their groove on, and then protect your trees.
The products I've seen most often recommended for protection against cicada attack are cheesecloth and netting that's often used to protect crops like blueberries from marauding jays and the like. These guys (TGN's Pumpkin Nook) actually show some of their products in action, shielding trees and shrubs from cicadas.
3. Most sites suggest that pesticide application should not be employed.
