Pests and Diseases
Noni Sooty Mold
Black sooty mold covering noni leaves.
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
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
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.
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 ones 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