The leaves of a redtwig dogwood started showing small holes, and now
some of the leaves are totally eaten out and dead. They're littered
with the bodies of very small white winged insects. The undersides of a
few leaves are covered with worms (larvae?), many of them lying flat in
adjacent perfect little 1/4-inch spirals that would be a nice pattern
if they weren't a nasty moist pale gray with a mildewy look. Some of
them are stretching out and wriggling, though. Very high yuk factor.
1. What is this?
2. What kind of measures should I take to get rid of them? (I'd prefer
not to spray.) If I just cut off the branches with the larvae, will the
plant have the same problem next year? (I live in E. Central Illinois,
so we're sure to have some good freezes.)
3. Have the insects finished their life cycle for this year, or will
there be more waves of them laying their eggs?
4. Will this infestation ultimately destroy the redtwig, or will it
just play itself out this year, even if I do nothing beyond cutting off
the infested branches?
5. There's an aggressive gourd plant next to the dogwood (planted
itself from a decorative gourd from last Halloween), and somehow the
flying insects seem to belong there. I've lots of other redtwigs, but
this is the first I've ever seen this kind of infestation.
I emailed the extension service and just received the following reply:
"Based on your description, the insect is the dogwood sawfly. Use
carbaryl to control them. Continued defoliation increases the risk of
canker and the red twig dogwood is already a highly canker prone plant."
Here's a site with a good photo:
There's only one generation per year, and since most leaves are not
affected I'll just remove infested leaves/branches and hope they won't
be worse next year. If necessary I'll remove the whole shrub. I got it
very cheap: I'd stuck some bare branches in a planter for winter
interest, and they rooted.
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