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The Great, Sweet, Sticky Precipitation Event of 2012

By: Brillig , 6:00 PM GMT on August 17, 2012

This year will go down as a record year for precipitation of a different sort.

All over town, people have been complaining about their vehicles and plants being sticky. Are their plants dripping sap? Are they sick? What about the mold everywhere? What can I do about it?

The culprit is aphids. Aphids are not unusual. In fact, this same sort of infestation happens every year with pecans and crepe myrtles. But never has it been as bad as this year.

Here's how it works. Aphids survive on plant fluids. Contrary to what most people think, they don't suck fluids from the plants. They simply pierce the plants. The plants actually pump the fluids into their bodies. In fact, the plants are so efficient at pumping the fluids that they pump the aphids up faster than they can metabolize the fluids. The excess is secreted as honeydew.

The honeydew gathers as a droplet at the end of their abdomens until it is too big to remain there. Then it falls off. The result is honeydew precipitation.

Since honeydew is mainly plant sap, the sugar content is very high. It lands on objects, including upper surfaces of leaves, roadways, and cars. As the water evaporates, it turns into a sticky, syrupy substance that dirt sticks to. While it still has some moisture content, mold takes hold, taking advantage of the free food supply.

Overnight as temperatures cool, dew forms on cold surfaces, including the accumulations of honeydew. In this say, the honeydew gets reconstituted each night, thus encouraging the growth of the fungi.

Staff at a local car wash have reported that these fungi can actually stain the clear coat finish of cars.

Current forecast shows rainfall this weekend. Perhaps it will wash away the layers of honeydew that have accumulated for the last month or so.

Chinkapin Oak Leaf (Brillig)
Honeydew from aphids covers top side of chinkapin oak leaves.
Chinkapin Oak Leaf
Honeydew "Shadow" (Brillig)
Driving around town, there are many places where there appears to be a shadow in the road. This is actually fungus and dirt in the honeydew that has fallen from the tree roughly above the spot. Look carefully. You can see a clear actual shadow in addition to the honeydew shadow.
Chinkapin Oak Leaf (Brillig)
Small aphids on lower side of chinkapin oak leaves.
Chinkapin Oak Leaf

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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1. Bogon
5:28 PM GMT on July 17, 2013
Thanks for posting this information. I think this explains what's been going on with my car, porch furniture etc. Didn't know the critters got on oak trees.

Next question: how do I spray, fumigate or otherwise treat a whole tree?
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