Gardening Questions Answered
Ants in Citrus Tree
There are ants crawling in my citrus tree and sticky stuff on the leaves and fruit. There is black sooty substance on the fruit itself. What is this?
The ants are feeding on the honeydew (the sticky stuff) excerted by the scale and are herding the scale and driving off beneficial insects that would prey on them. The black stuff is sooty mold instigated by the presence of the honeydew. To help control scale, you must control the ants. Use a sticky barrier product like Tanglefoot ™ or Stickum ™ to trap the ants. Follow the directions carefully. You can also use a boric acid bait or an ant bait. Diazinon is no longer recommended because traces are showing up in the ground water. Spraying with insecticides is not recommended since it kills off the beneficial insects such as lady bugs and parasitic wasps which pray on the scale. Scale populations tend to increase dramatically after pesticide use. Sooty mold can be washed off the fruit. The fruit is still edible.
UC Pest Management Guidelines:
Ants on Citrus
Citrus Black Scale
Citrus Cottony Cushion Scale
California Red Scale and Yellow Scale