cacao pod rot · üblack pod rot of cacao is caused by phytophthora üseveral species of...
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Black Pod Rot of Cacao
Emilie Kirk
Assistant Extension Agent
Sustainable and Organic Agriculture
UH CTAHR Kauai Cooperative
Extension Service
Roshan Manandhar
Assistant Extension Agent
Invasive Species
UH CTAHR Kauai Cooperative
Extension Service
ü Black pod rot of cacao is caused by Phytophthora
üSeveral species of Phytophthora can cause this disease
üP. palmivora is the most common one
üBlack pod rot causes 20-30% pod loss annually around the world (Acebo-Guerrero 2012)
üCanker can kill the trees
Disease
Symptom Development – Black Pod Rot
Initial Infection – small brownish or
dark spot(s) at the point of infection
Spread of infection – rapidly across the outer
surface
Symptom Development – Mummification
Infection covering
entire pod
Pathogen moves
deeper into the pod
Infection of cacao beans –
source of secondary infection
Symptoms Development – Canker
Dark spot on the bark that
oozes out reddish fluid
Infection under the bark
Symptoms Development – Branch die-back
Due to girdling by canker
Dead leaves, branch die-back
(Torres-Londono 2016)
Persistence in the environment
Sporangia – germinate directly on plant surface
Zoospores – in soil water or water on plant surface
until they find entry point (ie. wound)
**Zoospores reproduce sexually à genetic
recombination and evolving resistance
Chalmydospores – survive for months in soil or
dead plant material
Disease Management – Prevention
ØSite selection: Sites with relatively low rainfall and good drainage is recommended
ØQuarantine: Avoid transporting soil and plant parts from diseased area into new
clean areas
ØResistance: Varieties with fruit having thicker cuticle are more resistant
ØSpacing and pruning: trees should be well spaced and periodically pruned to allow
airflow in and around the orchard. Reduce humidity
ØMulch: leaf mulch will reduce splashing water when it rains, that minimize disease
spread
Disease Management – Sanitation
ØInfected pods should be removed and destroyed
ØClean tools and equipment
Disease Management – Treatment
ØFungicides:
- Copper based fungicides (a.i. Copper hydroxide) are useful for
controlling fruit rot and canker
- May not be cost effective
- Alternatively, systemic fungicides (a.i. Metalxyl) effective against
pod rot and canker, but expensive.
Disease Management – New approaches
ØPlant nutrition:
- Use of cacao pod husk (rich in P
and K) as a soil amendment
helped increase plant growth and
suppress pod rot disease in cacao.
Disease Management – New approaches
ØPlant nutrition:
- Spraying or drenching of phosphoric acid based fertilizers is found
effective for Phytophthora management in other fruit trees.
- Soil organisms, Trichoderma (fungus), and Actinomyces and
Pseudomonas (bacteria) have beneficial effects on plant growth
and inhibits Phytophthora in cacao.
- Further research is needed to validate these findings in Hawaii.
