White Mold on the Branches of an Orange Tree

Citrus Snow Scale

• Gardeners may mistakenly believe that white mold is growing on the branches of an orange tree when the object is actually the white bodies of two species of scale insects. The citrus snow scale (Unaspis citri) is so named because of the snow white color of the armor that adorns the male of the species. Snow scale exist primarily on the branches and trunk of an orange tree, sometimes blanketing the limbs en masse and giving the entire appendage a distinctive, white appearance.

Snow Scale Damage

• Citrus snow scales sap the tree of vigor and only stray from the branches when the infestation is severe. At that point, they will seek out and inhabit leaves and fruits. As the infestation worsens, the orange tree will prematurely defoliate, large cracks develop in the bark, limbs and branches die, and the entire tree may be killed. While males are easy to see, the armor of females is mahogany in color and camouflages easily against tree bark.

Cottony Cushion Scale

• The cottony cushion scale secretes a white, cottony, wax-like substance that coats its body. Adding to the illusion of what may appear to be white mold on the tree, the female cottony cushion scale drags behind her body a long, white egg sac covered with the same white, cottony secretion. The egg sac is typically twice as long as the insect herself and she lays between 500 and 800 eggs. Although a male cotton cushion scale exits, the female is able to fertilize herself.

Cushion Scale Damage

• The cottony cushion scale feeds on the tree causing the premature defoliation of leaves, dropping of fruit and a loss of vigor to the tree overall. Initial damage is caused by immature stages of the scale. As it ages, the insect migrates from leaves to twigs and by the time it reaches adulthood, large patches of cottony cushion scale envelop the limbs and branches of an orange tree, forming a collection of insects that may appear to be a batch of white mold.