Q: My young meyer lemon tree’s leaves have black sooty stuff all over them. What do I do to help?
A: When a reader who requested to remain anonymous asked about odd sooty stuff on her lemon tree leaves, we were curious and set out to find out what was going on.
We reached out to Walter Earle, the nursery manager at the Laguna de Santa Rosa Foundation environmental center, and found out that black sooty mold is usually a sign of aphids.
It’s usually a sign of aphids or scale attacking the plant, he said. “A good clue is to look for ants on the tree as they ‘farm’ the aphids to collect their sweet honeydew to use as a food source.”
Due to the honeydew secretions from the insects a mold fungus forms on the leaves overtime, resulting in the black sooty appearance.
While the aphids on the plant are the biggest concern, the black-coated leaves can also blackout sunlight, which can stunt the tree’s growth.
Earle, who has 40-plus years of experience as a horticulturist and nursery owner in Tomales, said the best way to get rid of the bothersome critters is to blast the affected areas with soapy water.
“A strong blast of water often works to knock some of them off. Also a spray of soapy water — one or two tablespoons of dish soap/gallon of water — will deter the pesky critters. Safer makes an insecticidal soap that can be purchased at a garden center. This also works,” Earle said. “Some of these products contain Neem oil which is organic and safe,” Earle said.
“Scale are more difficult to kill but the water blast can work to reduce their numbers,” he added.
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