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Pests and Diseases
Noni Sooty Mold
black sooty mold
Black sooty mold covering noni leaves.
noni leaf with sooty
Close-up of noni leaf with sooty
mold and the associated scale insects
along the main vein and some secondary
veins. The green scale feeds on sap
within the noni leaves and then excretes a
sugary waste-product referred to as
“honeydew.” The honeydew is a sticky
substance that covers the noni leaves. The
honeydew is a source of food for the black
sooty mold fungus, which grows over the
surface of the leaf, blocking sunlight
but not penetrating the leaf, as
pathogenic fungi are able to do.

Condition: Sooty mold.

Organism: Sooty mold is caused by a ubiquitous, airborne fungus that lands on the noni leaves and uses the sugary exudates produced by sap-feeding insects as a food source. Thus, the presence of high populations of sap-feeding insects is necessary for the formation of sooty mold.

Symptoms/Signs: Sooty mold consists of a black, powdery growth, usually on the upper surface of noni leaves. The black growth is not pathogenic (it does not penetrate leaf tissues) and exists as a thin layer that can be scraped off with one’s finger or washed off with soapy water.

Distribution: The sooty mold fungus is ubiquitous and exists presumably on all the Hawaiian islands. The sooty mold condition is associated with sap-feeding insects such as aphids and scales.

Damage potential: Sooty mold on leaf surfaces can block sunlight from reaching the leaves, reducing photosynthesis and plant vigor. The sap-feeding insects associated with sooty mold cause more damage to noni plants than the sooty mold.

Control: To control sooty mold, one must control the sap-feeding insects (scales, aphids) which infest the noni plant. Often, the control of these sap-feeding insects can be greatly improved by controlling the ant species which tend to them and also use the honeydew as a food source. Sooty mold may in some cases be washed off noni leaves with a strong spray of soapy water.

Last Updated on December 7, 2006