Sep 16, 2022 - News

Aphid secretion coats Austin

An aphid. Photo: Auscape/Universal Images Group via Getty Images

Struggling with sap that covers your lawn and car? You're not alone.

The big picture: Axios Austin reader Mary Catherine S. asked us about a sticky, thin layer of sap on her car that she's never seen before.

  • "I've parked under the same pecan tree in East Austin for three years and never experienced this before! The stickiness is also now covering the handrails along my front steps; it's pretty crazy!"

We reached out to Joe Marcus, program coordinator of the Native Plants of North America at the Lady Bird Johnson Wildflower Center, who explained what's happening.

Be smart: The sticky residue isn't tree sap. It's honeydew — a sugary liquid secreted by aphids, who feed on tree leaves, Marcus told us.

  • Aphids suck on the leaves — almost like a mosquito — and then excrete honeydew.
  • The insects are found on many plants but are especially noticeable on pecan and crepe myrtles in Texas.
  • And there's a whole ecosystem around this. Ants love to snack on the honeydew and rub the backs of aphids to stimulate the insect to excrete a droplet.

Of note: Honeydew won't kill your trees, but it's a pain and it often leads to sooty mold fungus growing on the top of the dew.

  • That fungus blocks sunlight from getting to tree leaves and slows its growth. Marcus said he's never known sooty mold to kill a tree.

Pro tip: Natural predators like ladybugs and ladybird beetles can be released into a backyard to eat the aphids.

  • Rain also helps wash away the honeydew. (Marcus suggests doing a rain dance.)

The bottom line: "It's a pretty complicated thing, but it's very common this time of year," Marcus said.


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