6. Symptoms
Chlorotic and necrotic spots; dead
leaf tip; defoliation; brown or purple
lesions on new shoots
Cause
Fungus
Comments
Spores spread by rain splash; high
moisture and warm temperatures
encourage spread
Management
Prune dead twigs and branches from
tree before fungi produce spores;
knock dead leaves out of canopy;
keep harvested fruit dry and cool
Chloratic Disease
8. Symptoms
Oval or irregular brown or
purple spots on fruit with
rough texture
Cause
Fungus
Comments
High humidity encourages
scab growth and spread
Management
Plant tolerant varieties; spray
with copper containing
fungicides
Purple Spot
9. Symptoms
Elongated black streaks on bark; cankers
parallel to growth of limbs; black blotches
with distinct margins on green wood;
cankers on bark cause cracks which ooze
sap; removal of bark over cankers reveals
dark discoloration underneath
Cause
Unknown
Comments
Disease emergence favors adverse growing
conditions for avocado; more common in
Guatemalan cultivars
Management
Avoid stressing trees by following good
fertilization and irrigation practices
Black streak Avocado black streak
10. Symptoms
Black lesions on roots; black, brittle roots;
small, yellow leaves; premature leaf drop;
decline in fruit yield
Cause
Oomycete
Comments
Wet soils encourage Phytophthora
infection; plant in a well draining soil.
Management
Minimize water splash between trees by
not working in a wet orchard; prune out
dead limbs and twigs; remove fruit from
the ground; dispose of dead wood and
fruit away from trees
Phytophthora root rot and crown rot
Phytophthora cinnamomi
11. Fruit symptoms of P.
citricola
Tree trunk with symptoms
of Phytophthora citricola.
Phytophthora
12. Symptoms
Shrivelled tissue at stem end; dark brown
or black lesions at stem end and
eventually over entire fruit; fruit covered
in mycelium
Cause
Fungi
Comments
Environmental conditions may determine
which fungal species is most common;
spores can spread by wind or rain.
Management
Prune dead limbs and twigs; prune and
harvest in dry conditions; provide trees
with sufficient irrigation; apply a thick
layer of mulch
Stem-end rot
13. Symptoms
Symptoms
Gray to black, mushy, foul smelling rot on fruit;
fruti has darkened metallic sheen
Cause
Bacteria
Comments
Bacteria may be present on leaves but do not
cause damage unless plant is stressed or bacteria
enter the plant through a wound
Management
No treatment for disease; use certified seed;
disinfected tools and cuttings; employ crop
rotation; remove plant debris from soil
14. Symptoms
Red, yellow, pink or white streaks
running the length of young
stems; white, yellow or red
blotches on fruit
Cause
Viroid
Comments
Can be transmitted by grafting
Management
Frequently sanitize all pruning
equipment with disinfectant;
plant only certified nursery stock
Avocado sunblotch viroid (ASBVd)
16. Symptoms
Algal leaf spot symptoms
Raised, orange-red spots
on both upper and lower
surfaces of leaves; spots
may coalesce to form
irregularly shaped
patches; spots may also
be present on twigs and
branches; when the
surface of the spot is
scraped away, a gray to
dark necrotic crust is
visible
Algal Leaf Spot