Rumor has it that maple petiole borers may be the culprits making leaves of sugar maple trees to fall and drop too early. The borer is an invasive sawfly or non-stinging wasp that emerges from the soil as leaves expand in the spring. Eggs laid at that time soon hatch and the resulting larva mines petioles of maples, especially sugar maples for about a month. The mined petiole weakens and breaks, sending a green leaf blade with a blackened petiole stub to the ground.
The petiole remaining on the tree also drops a week or so later. In that portion of the petiole is a larva that exits and burrows into the ground to pupate and become an adult the following year.
Typically, infestations are low, however, authorities are saying that this year about 25% of leave are dropping on some trees. This is increase from less than 10% of leaves dropping in prior years. While green leaves on the ground is causing concern, the actual number of leaves involved is not worth loosing sleep over. If you want more information on horticulture, call the garden helpline located in Rochester NY at (585) 473-5335 from 9AM – NOON (EST) Monday through Friday.