Throughout the time that plants are growing and active, you often see things that make you wonder what is going on with the plants. Sometimes, plants look a bit like they have a runny nose, or a drippy eye. If you are like me, you might take a second look to set things straight in your mind.
Over the past few weeks, you might have noticed that vehicles parked under larger trees have a slight stickiness, or a spattering of tiny drops on the windshield or roof. I noticed that a tree in the park across the street from me had leaves that appeared glazed or somewhat shiny, beyond that which you might associate with a normal waxy leaf.
I also noticed that a number of aspens in a grove that I walk by regularly have an oily ooze discolouring parts of the trunk, originating around various holes.
What is the cause of these strange drips and oozes? The short answer is insect feeding.
Honeydew (sticky sap, not the matrimonial chore list)
Over the years, I have had the occasion to notice a sticky rain of sorts from the larger street trees in my community (and elsewhere). This year, it is a fine mist of stickiness settling on vehicles. Several years ago, it was like a heavy shower that coated vehicles and lower leaves in a solid layer, and left a large, sticky “rain shadow” under each tree. You could actually stick to the road if you stepped or biked onto it. It was unreal.
If you take a close look at the lower leaves of the big trees, or in the case of this poplar in the park, you will notice that there are a number of leaves that are puckered and curled up in a bubbly-sort of way. Inside you would notice a writhing mass of little juicy insects of all sizes, as well as a perhaps some webbing, fluffy wax and/or debris.
In this case, the culprit is our friend the aphid. She and her thousands of girl family are happily piercing and sucking out the sap and sugar-rich juices from the leaves, and then letting it out the back end in an inefficient manner. This sticky sap, called honeydew, will fall, drip or flow down the plant to the surfaces below. In some cases, you will see a sooty black mold form on this food source. In lots of cases, you will see ants taking advantage of these inadvertent “sap harvesters”, essentially farming the aphid colony.
What do you do about it? Well, if you can get past the sheer area of real estate occupied by the entire population of the colony in a massive street tree, you might treat them with an insecticidal soap or perhaps another insecticide. Or, you can just let things progress naturally, with the population declining over time as the natural illnesses, predators and parasites catch up. Rain will take care of most of the stickiness.
Here is some more information on APHIDS.
Tree paint
In some places, the leaking sap I am referring to is described as a “varnish-like” liquid that stains the trunk. It is the product of the tree in response to feeding by the boring (tunneling insect, not “uninteresting”) POPLAR BORER. As the larvae of the insect grow, they feed within the trunk of the tree, ejecting sawdust from the hole. The tree responds to the ongoing wounding by excreting a dark, sticky sap. As the developmental process of the larvae is several years, the sap flow can become quite noticeable, as can the sheer number of holes on a tree (since the insects tend to stay close to where they grew up).
What can you do about it? Not a whole lot. Some of the population will be taken out by natural means, but this pest is definite problem out in the Aspen Parkland region. I find that it is becoming increasingly more rare to see a poplar or aspen that does not have signs of a poplar borer infestation.
