Maple Petiole Borer Damage
The following description of the maple petiole
borer and subsequent leaf drop was written by
Lee Townsend, Extension Entomologist, Univ. of Kentucky, Lexington.
drop of many sugar maple leaves may be due to injury by a small wasp larva
that burrows in leaf petioles (stems). The stems usually break at a darkened
area near the leaf blade.
Usually infestations are limited to sugar maples
and only about 25% to 30% of the leaves fall to the ground. While
spectacular, the leaf drop has little effect on tree health.
Buildups of scales or aphids, or drought stress can cause leaf
loss but these typically occur later in the year. Leaf drop due
to borers is seen earlier in the season and the leaf blades may
still be green. Leaves from trees stressed by sucking insects
or drought usually have turned yellow before they drop. Splitting
the petiole carefully near the leaf blade should reveal the
larva or the tunnel.
There is one generation each year. Infestations
begin as the adults, small wasps about 1/6" long, appear
in May and lay their eggs in petioles near the leaf blades. Legless,
white grubs with distinct light brown heads hatch from the eggs
and tunnel inside the leaf stem for 20 to 30 days. The weakened
stem breaks and the leaf floats to the ground.
The borer larvae
generally remain in the portion of the stem left on the tree.
About 10 days after leaf drop, the rest of the stem falls to
the ground. The mature larva, about 1/3" long,
leaves the stem through a hole in the side and burrows into the
soil. It will change to the pupal stage and remain in the soil
until the following spring.
Maple petiole borer infestations are infrequent
and unpredictable. Also they do not appear to harm tree health
so insecticidal control is not recommended. In addition, probably
preventive treatments, applied well before leaf drop, would be
necessary. It may be possible to reduce future infestations by
picking up and destroying infested stems, the short sections
without leaves, about 7 to 10 days after the first leaves fall.
This sanitation program needs to be continued throughout the
leaf drop period and must include all infested trees in the vicinity
to be most successful. Raking and disposing of the leaves will
not reduce the population because the insects are not in that
For more pictures of maple petiole borer damage,
please click here.
Photos courtesy of
Mick and Connie Hardy,
The information given herein is supplied with the understanding
that no discrimination is intended and no endorsement by the
Purdue University Cooperative Extension Service is implied.
Any person using products listed assumes full responsibility
for their use in accordance with current direction of the manufacturer.
Purdue University is an equal opportunity/equal access institution.
Information listed is valid only for the state of Indiana.