Conestoga House & Gardens, 1608 Marietta Avenue, Lancaster PA
Probably few large Cottonwoods are in Lancaster County, and with a 2018 trunk circumference of 14 feet 3 inches, this tree may be the county’s largest. (The state champ in Halifax is a monster, however: more than 30 feet in circumference.)
"Our Cottonwood," said CH&G caretaker David Kantner, "has cotton only sparsely and not reliably each year. It used to produce more cotton but may have lost a local male companion or perhaps is not flowering very heavily."
The petiole gall seen here is Pemphigus, an aphid. These insects overwinter as eggs on Cottonwood twigs. When the leaves unfurl in the spring, nymphs hatch and feed on the leaf petiole. The tree responds by producing localized growth which becomes the gall; this gall protects the largely immobile nymphs from insect predators and the weather. Eventually the gall splits open and winged adults fly out.
This amazing species (Cottonwood) consumes large amounts of water in its growth cycle, as much as 200 gallons a day. If its root is cut, the tree will “bleed” water for days until the wound heals.