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Diseases of forest trees in Kenya
By
Linus M. Mwangi
Kenya Forestry Research Institute

Introduction
• Several diseases occur in forest plantations
and nurseries in Kenya
• Types: leaf spots, cankers, mildews and root
rots
• The IPM section of KEFRI is mandated to
carry out research and advisory service on
pests and diseases
• The major diseases found on plantation
trees are presented here

Leaf spots
• Found in nurseries
and plantations
• Caused by
Mycosphaerella
species
Eucalyptus
Vitex keniensis
Spores

Dothistroma needle blight
• Arrived in Kenya in early 1960’s
• Affected P. radiata an exotic tree
• Caused by Mycosphaerella pini (Dothistroma
pini)
• Forms red bands on needles
• Affected needles turn brown and fall
• In 1962 planting of P.radiata was stopped due
to the disease

Symptoms
P. radiata and P. patula
P. radiata
Young trees

% of trees
Management
• Earlier trials involved
use of copper based
fungicides
• Trials were later set up
with locally selected
materials and those
obtained from
Newzealand
• Monitored for disease
severity.
• Found the level not to
affect growth to a big
extent
• Planting restarted
50%
40%
30%
20%
10%
0%
Fig. 3 Percentage of trees in various disease scores-
Kaptagat plot
1 2 3 4 5
Disease score
March
June

Powdery mildews
• Can occur in the nursery or field
• Affect the leaves
• Cause stunted growth and leaf fall of trees
• Symptoms- whitish appearance on surface
of leaves.

Powdery mildews
Prunus africana
Eucalyptus

Botryosphaeria canker
• The most common disease
of Eucalyptus in Kenya
• Symptoms: Production of
gum and cracking of stems
• Mainly found on E.
grandis and E.
camaldulensis,
• Some GC clones now
being affected eg GC540,
GC522, GC14 and EH
among others
E. grandis
E. henrii
GC 540

Botryosphaeria symptoms on Grevillea
robusta

Diplodia pinea (Sphaeropsis
sapinea)
• Diplodia pinea (Desm.) Kickx is a destructive
pathogen of pines
• The disease occurs on trees from 5 years or
older trees (Roux et al, 2005).
• Damage to trees includes shoot blight, branch
and stem cankers
• The cankers exude copious amount of resin
from stems and branches.
• The fungus also causes blue stain on timber

• A few years ago
most of the P.
patula
plantations were
clear felled
• Incidence of the
disease is low in
most plantations.
• Found on
remnant
plantations
Pinus patula

Armillaria root disease
• Attacks a wide
range of tree
species
• Cause mortality
in plantations
especially on
pines
• Species: A. hemii,
A. mellea
P.patula

Conclusions
• Kenya like other countries have been affected
by various disease problems.
• Only the major diseases have been covered
but more diseases do exist
• A lot of effort has been put on research,
monitoring and advice on management
strategies