College of Tropical Agriculture and Human Resources
overview button
botany button
natural habitats button
horticulture and production button
harvesting and processing button
pest and diseases button
health-related research
review articles button
2002 conference button
bibliography button
new button
search button
Pests and Diseases
Noni Black Flag
disease noni tree
Disease noni tree in a forest understory in Puna with greater than 95% collapsed leaves.
blackened stems
Characteristic “black flags” (collapsed, necrotic leaves) and blackened stems associated with noni black flag disease.
blackened noni fruit
Blackened noni fruit infected with Phytophthora.

(For more complete information on noni black flag and a free online publication, visit

Disease: Noni black flag.

Pathogen: Noni black flag is caused by a Phytophthora sp. (tentatively identified as Phytophthora botryosa, a fungus-like organism). We do not yet know the host range of this pathogen.

Symptoms: Foliar symptoms of noni black flag include: black leaf spots and leaf blight; brown to black stem blight; brown to black soft rot of fruits; fruit mummification; severe defoliation (hanging, diseased leaves are referred to “black flags”); blackened leaf veins; death of stems; plant death. Roots and woody portion of the plant are not normally infected.

Impact: Noni black flag is a major threat to noni farms in areas where the disease it occurs. Large yield losses and even plant death are possible.

Disease distribution: Noni black flag was first discovered in 2000 in the Puna district near Opihikao on the island of Hawaii. The disease is not known to exist elsewhere in Hawaii or in the world.

Epidemiology: Noni black flag is favored by frequent rains, high winds, warm weather and high relative humidity. Spores are dispersed by splashing rain and wind.

  1. Learn to recognize black flag disease symptoms and inspect noni plants regularly during and after periods of extended rainfall.
  2. Promptly prune, remove and destroy symptomatic foliage and fruits to reduce pathogen inoculum levels and to minimize the likelihood of disease spread.
  3. Remove fallen or pruned branches, stems, leaves and fruits. Do not allow them to accumulate beneath noni trees.
  4. Promote air circulation within the noni canopy to ensure rapid drying of leaves and fruits. This can be accomplished by selecting wider plant spacing during farm establishment, and by pruning back verticals to open up the canopy to increased air movement.
  5. Reduce relative humidity within the noni canopy. Prune back overhanging trees. Ensure good soil drainage. Control weeds around the noni plants. These measures will ensure rapid drying of leaves and fruits after rainfall, reduce water congestions in plant tissues, and minimize the infective potential of the pathogen.
  6. Avoid introducing diseased noni plants or fruits into high-rainfall areas where the disease has not been reported. Start new noni farms with disease-free plants.
Notes: Noni black flag was previously unreported to occur in Hawaii and elsewhere in the world.

Last Updated on December 7, 2006