A Sticky Situation | Aphids, drought make mess of some Snoqualmie streets, sidewalks

Have you gone for walk around Snoqualmie lately and come home with sticky shoes or leaves attached to the bottom of your shoes?

Wonder what is going on with numerous trees around town… the ones dripping a sticky, sap-like substance onto streets and sidewalks at a seemingly relentless pace?

The cause of Snoqualmie’s sticky streets, sidewalks

According to an explanation on the City of Snoqualmie website, it’s not actually sap dripping from the leaves. Rather it’s the work (i.e. excretions) of aphids. Those tiny aphids are sucking the sugars out of the leaves and then excreting them (I know… eew.), causing a ‘rain’ of a sticky substance know as ‘honeydew’ onto streets, sidewalks and cars below.

[The affected streets and sidewalks are noticeably darker – like a shadow – and often have dead leaves stuck to them.]

Worse this Year

Stress from drought (and just tree stress in general) makes the problem worse, as stressed trees produce more sugars and thus attract more aphids. A hot summer with little rain had made the aphid problem noticeably worse this year.

But not every tree in the city is a sticky mess. According to city info, only 1247 street trees are affected – or 13% as Snoqualmie has a massive amount of street trees.

Working for a Solution

The city says it is trying to fix the problem. Linden trees are being phased out and as they die, replaced by a species more aphid resistant. Some (limited cases) individual streets are also being evaluated for possibly removing and/or replacing the affected lindens.

Pesticides have not been used because they can also kill bees which are essential to agriculture. The city stated it will also be conducting a trial of new biological controls for the aphids (natural predators for the pesky, tiny bug).

Autumn is coming soon and leaves will be falling – so this is not a permanent problem. In the meantime, if you have an affected tree on your street, spraying it with water may help. The water stream can knock off or kill many aphids on the leaves, as well as wash off that honeydew that is attracting them to the tree in the first place.

Secondary problems also caused by that ‘honeydew’: 

• Create a fungus, black sooty mold to develop on the trunks and branches of trees, which looks unsightly but not harmful to the tree.
• Various insects, including some wasps, are drawn to honeydew
• Ants “farm” the aphids, and protect them from natural predators