Walnut diseases A Lecture on ToT By Allah Dad Khan

2. Walnut Diseases
A
Lecture To ToT trainees ( FFS)
By
Mr. Allah Dad Khan
Provincial Coordinator IPM KPK
MINFAL Pakistan

7. Walnut blight Xanthomonas campestris
Symptoms
Blossom damaged by walnut blight
 Small, water-soaked spots on
immature fruit which darken and
rapidly enlarge; bacterial exudate
may be present during wet weather;
if infection occurs prior to shell
hardening then the kernels shrivel;
infections which occur later may
cause kernel discoloration but the
fungus does not usually invade the
kernel; catkins which become
infected are are dark and shrivelled;
new shoots may also be attacked
and lesions may girdle the stem,
killing the shoot above; lesions may
form on tree bark and may also
extend into the pith causing
cankers to form; lesions on leaves
are brown with a green-yellow
perimeter; leaf lesions may
coalesce to form large necrotic
areas

8. Anthracnose Gnomonia leptostyla
Symptoms Anthracnose lesions on black
walnut leaves
 Brown to black lesions on
leaves, petioles, shoots
and/or husks which fade
toward the center and may
be surrounded by a
chlorotic halo; spots may
coalesce to form large
necrotic patches, usually
located close to leaf
margins; lesions on shoots,
petioles and leaf midribs
become elongated and
sunken

9. Phytophthora root and crown rot
Phytophthora spp.
Symptoms
Phytophthora Crown Rot.
 Slow growing trees with
reduced vigor; leaves of tree
turning yellow and wilting;
shoots and branches dying
back; if tree is girdled at the
trunk or root crown then death
occurs, usually within one
growing season; infected tree
roots are necrotic and
discolored black or brown; most
roots eventually die; trees with
crown rot may exhibit cankers
of the root crown which extend
above the soil line; cankers are
visible as discolored bark and
possess a zonate appearance
when the bark is removed

10. Armillaria root rot (Oak root fungus)
Armillaria mellea
Symptoms
Armillaria root rot.
 Small, discolored leaves which drop
early; death of branches; death of plant;
clusters of honey-colored mushrooms
may sprout at base of plant
 Cause
 Fungus
 Comments
 Fungus survives on dead roots in soil
 Management
 Armillaria root rot cannot be effectively
controlled once it has become
established in an orchard; diseased or
dead plants should be uprooted and
removed; planting resistant rootstocks is
the most effective method of preventing
the disease

11. Blackline disease Cherry leaf roll virus (CLRV-W)
Symptoms
Blackline Disease.
 Gradual reduction in tree
vigor; leaves are yellow
and drooping; defoliation
occurs prematurely and
is followed by dieback of
terminal shoots; small
holes or cracks may be
present at the graft union
and underlying tissue
may be discolored

12. Powdery mildew Phyllactinia guttata
Symptoms
 Small, powdery white
spots on leaves and fruit;
spots spread to cover
entire leaf; small black
fungal fruiting bodies
may be visible in the
white growth; young
leaflets may crinkle as
they mature

13. Disease of walnut tree - yellow spots
Our walnut tree developed
a conditiow with yellow
spots all over the leaves
last Summer. Will it harm
the tree? What is it? Do
we need to treat the tree
to prevent a recurrenc

14. Walnut (Juglans spp.)-Downy Leaf Spot
Symptoms
The sporulation of the fungus can
been seen on the under side of the
leaves.
Lesions are soft to bright yellow on the
upper surface and angular following
leaf veins. The corresponding areas
on the undersurface are chalky
white where the fungus is
sporulating. Lesions become
necrotic with age and may coalesce
causing the leaf to turn brown and
dry. Infection of young leaves may
be distorted. Rarely symptoms on
fruit may be seen as small, circular
downy area on the hull. The lesion
grows as the fruit grows. The edge
may be downy at first but then turns
dark brown to black. The result is a
wide dark circle with a lighter green
center with a sunken margin.

15. Crown Gall
Symptoms

Crown gall is a disease that results in
round to irregular swollen tumors or
galls, usually found at or near the soil
line on the trunk or roots. Infected
trees show a lack of vigor, foliage
lacks normal green color, and
occasionally the tree may die. To
prevent crown gall, plant disease-free
trees. For individuals with a small
pecan nursery, it is important not to
locate a nursery in an area where
crown gall has been observed
previously. As a preventative control
measure, it would be advisable to
treat the seed with Galltrol-A before
planting

16. Crown Gall

17. Zonate leaf spot Grovesinia pyramidalis
Symptoms
Zonate leaf spot lesions on pecan leaflet
 Lesions with concentric
rings on leaves which are
tan to light brown on the
leaf underside and gray-
brown on the upper leaf
surface; a crystalline
substance may be present
on the surface of the lesion;
infected leaves dry out by
late summer and drop from
the tree prematurely;
defoliation may be severe

18. Zonate leaf spot
Zonate leaf spot symptoms on pecan
leaf
Close-up of zonate leaf spot lesions
on pecan leaflet