What is the sticky substance covering the ground and leaves at the cottage?
That sticky mess is called honeydew, which is a charming name for the not-so-charming excrement of scale insects. (Or possibily the excrement of aphids). There are many species of these insects, which are convex creatures, about 3 to 6 mm long with hard, dark shells that hug branches. They spend their summer sucking sap out of hardwood trees, usually oak or maple, and excreting copious amounts of sweet, clear, sticky fluid as a by-product. This honeydew drops through the trees onto lower branches and the ground.
Scale infestations have occurred in the southern part of Ontario as a result of the exceptionally hot and dry growing seasons for many of the last summers. Although no one has data on exactly where the outbreaks are, it’s safe to say that many trees are under stress, and so they are vulnerable to scale infestation. Another scale insect that has been reported is the oyster shell scale, which attaches to beech and ash trees—and yes, looks like a small oyster shell.
As if that sticky stuff these insects produce isn’t bad enough in itself, it may attract more wasps, bees, and ants. It’s also a breeding ground for sooty mould: Wind-blown spores stick to the honeydew, where they germinate and send out black strands.
While messy, the scale infestation isn’t necessarily damaging to the trees, although you may notice some dieback on the ends of limbs. Since trees take years to recover from the underlying stress, the ones in your area will need a few good growing seasons to make them strong again. As well, insects that feast on scale—such as parasitic wasps—will move in and clean up. Then you can go back to enjoying honeydew as a melon, not a mess.
