This document summarizes several diseases that affect zucchini plants, including powdery mildew, fusarium wilt, downy mildew, squash mosaic virus, witches' broom disease, angular leaf spot, bacterial leaf spot, bacterial wilt, and alternaria leaf blight. It describes the symptoms of each disease and provides recommendations for control methods.

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

3. Powdery Mildew (Sphaerotheca
fuliginea)
 first appear as white powdery
residue primarily on the upper leaf
surface. On the lower surface of the
leaves circular patches or spots
appear. In severe cases, these
spread, coalesce and cover both the
surfaces of the leaves and spread
also to the petioles, stem, etc.
Severely attacked leaves become
brown and shrivelled and defoliation
may occur. Fruits of the affected
plants do not develop fully and
remain small.
 Control: Carbendazim (1ml/litre of
water) or Karathane (0.5 ml/litre of
water) is sprayed immediately after
the appearance of the disease. 2-3
sprays are taken at an interval of 15
days
Symptoms:

4. Powdery mildew

5. Fusarium Wilt (Fusarium oxysporum f.
sp. niveum)
 Eventually, the plant dies. The
roots are not affected. In older
plants, leaves wilt suddenly and
vascular bundles in the collar
region become yellow or brown.
 Control: Three sprays of
Karathane (6 g in 10 litres of
water) or Bavistin (1 g /litre of
water) immediately on
appearance of initial symptoms
at 5-6 days interval controls the
disease. Leaves of fully grown
vines should be thoroughly
drenched during spraying.
Symptoms:

6. Downey Mildew (Pseudoperonospora
cubensis)
 The disease is first seen as
yellow angular spots on the
upper surface of the leaves.
Under conditions of high
humidity, whitish powdery growth
appears on the lower surface of
the leaves. The disease spreads
rapidly killing the plant quickly
through rapid defoliation.
 Control: Excellent control of this
disease can be achieved with
Ridomil (1.5 g/litre of water)
which must always be used
simultaneously with a protectant
fungicide such as Mancozeb
(0.2%) to prevent the
development of resistant strains.
Symptoms.:

7. Downy Mildew

8. Downy Mildew

9. Squash Gourd Mosaic
 appearing on the leaves in the secondary
branches produced at the apical end of the
plant. Small irregular yellowish patches are
seen on the leaves. Some leaves show
vein clearing in one or two lobes of the leaf
and severely infected plants show
reduction in leaf size and elongation and/or
suppression of one or two lobes. Young
developing leaves are completely distorted
and malformed with considerable reduction
in their size. Some of the leaves show
marked reduction in the development of
lamina resulting in a shoestring effect. The
virus is transmitted by five species of
aphids.
 Control: Spraying the crop just after
germination with Monocrotophos (0.05%)
or Phosphamidon (0.05%) at 10-day
intervals prevents aphid vectors.
Symptoms:

10. Witches' Broom Disease
 of this disease are malformation and proliferation
of axillary buds. Diseased plants show many
abnormally little leaves, which fail to attain full
size. The diseased plants bear many flowers and
blossom earlier than healthy plants. Flowers on
infected plants show characteristic green,
phyllody symptoms. Fruit formation is noticed
from the flowers partially infected with the
disease. Fruits from these flowers are very small,
cylindrical and deformed. The outer surface of the
fruits is smooth and fruits are completely
seedless. Plants showing severe witches' broom
do not bear any fruit.
 Control: Application of Carbofuran (1.5 kg a.i./ha)
at the time of sowing seeds followed by 5-6 foliar
sprays of either Phosphamidon (0.05%) or
Monocrotophos (0.05%) or Oxydematon Methyl
(0.05%) at 10 days interval, to control the vector
population. Spraying of Oxytetracycline
hydrochloride solution (500 ppm) at weekly
intervals suppress the disease symptoms.
Symptoms:

11. Angular leaf spot
Pseudomonas syringae
 Small water-soaked
lesions on leaves which
expand between leaf veins
and become angular in
shape; in humid
conditions, lesions exude a
milky substance which
dries to form a white crust
on or beside lesions; as
the disease progresses,
lesions turn tan and may
have yellow/green edges;
the centers of the lesions
dry and may drop out
leaving a hole in the leaf
Symptoms

12. Angular Leaf Spot

13. Angular Leaf Spot

14. Bacterial leaf spot
Xanthomonas campestris
 Dark, angular lesions
on leaves; leaf lesions
may coalesce and
cause severely blighted
foliage; water-soaked
lesions which enlarge
and develop into tan
scabs, or blisters, on
the fruit; blisters
eventually flatten as
they reach their full size
Symptoms

15. Bacterial leaf spot

16. Bacterial wilt

17. Bacterial wilt

18. Bacterial Wilt

19. Bacterial Wilt

20. Bacterial Wilt

21. Alternaria leaf blight Alternaria
cucumerina
 Small, yellow-brown
spots with a yellow or
green halo which first
appear on the oldest
leaves; as the disease
progresses, lesions
expand and becone
large necrotic patches,
often with concentric
patternation; lesions
coalesce, leaves begin
to curl and eventually
die
Symptoms

22. Anthracnose Colletotrichum orbiculare
 Tan to brown lesions with dark
spots inside on leaves and
petioles, main stem and fruit
 Cause
 Fungus
 Comments
 Disease favors warm weather
 Management
 Plant resistant varieties; use only
certified seed; apply appropriate
protective fungicides; rotate
crops every year
Symptoms

23. Anthracnose

24. Anthracnose

25. Gummy stem blight Plectosporium tabacinum
 V-shaped yellow to brown areas on
stem; cracked dry areas on stem;
lesions leaking a sappy material
 Cause
 Fungus
 Comments
 Disease may be seed-borne
 Management
 Use disease free seed; treat seeds
prior to planting; rotate crops every 2
years

Symptoms

26. Phytophthora fruit and crown rot Phytophthora
capsici
 Sudden wilting of plants; brown lesions on
stems and roots; rotting fruit; stunted plant
growth; downy growth may be present on
lesions during periods of high humidity
 Cause
 Oomycete
 Comments
 Disease emergence favored by heavy
rainfall and poorly draining, waterlogged
soils
 Management
 Do not plant in poorly draining soils; avoid
over-watering plants; rotate cucurbits with
non-susceptible plants for a period of at
least 3 years
Symptoms

27. Scab Cladosporium cucumerinum
 Angular brown lesions on leaves confined
by small veins; pale green and water
soaked lesions; holes in leaves from dried
out lesions; lesions may also be present
on petioles, stems and fruit
 Cause
 Fungus
 Comments
 Fungus survives in soil on crop debris;
may be seedborne; disease emergence
favored by wet weather and temperatures
below 21°C (69.8°F)
 Management
 Rotate cucurbits with non-susceptible
crops for a period of at least 2 years; plant
only in well-draining soils; spray plants with
appropriate protective fungicides
Symptoms

28. Scab

29. Verticillium wilt Verticillium dahliae
 Symptoms generally appear after fruit set;
chlorotic leaves which develop necrotic
areas; leaves collapsing; symptoms only
on one side of vine; discoloration of
vascular tissue in roots
 Cause
 Fungus
 Comments
 Fungus can survive in soil for many years;
disease emergence favored by cool or mild
weather in Spring
 Management
 Do not plant in areas where other
susceptible crops have been grown
previously; delay planting until
temperatures are warmer

Symptoms

30. Cercospora leaf spot Cercospora citrullina
 Initial symptoms of disease occur on older leaves
as small spots with light to tan brown centers; as
the disease progresses, the lesions enlarge to
cover large areas of the leaf surface; lesions may
have a dark border and be surrounded by a
chlorotic area; the centers of the lesions may
become brittle and crack
 Cause
 Fungus
 Comments
 Fungus survives on plant debris; spread by wind
and water splash; occurs mainly in tropical and
subtropical growing regions
 Management
 Any diseased plants should be removed and
destroyed to prevent further spread; crop debris
should be removed after harvest or plowed deeply
into the soil to reduce inoculum
Symptoms

31. Septoria leaf spot Septoria cucurbitacearum
 Initial symptoms of disease
are small dark water-soaked
spots on the leaves which
turn beige to white in dry
conditions; lesions develop
thin brown borders and the
centers may become brittle
and crack; small white spots
may erupt on the surface of
infected butternut and acorn
squash and pumpkin fruit
 Cause
 Fungus
Symptoms

32. Septoria Leaf Spot

33. Cucumber mosaic Cucumber mosaic virus
(CMV)
 Plants are severely stunted;
foliage is covered in
distinctive yellow mosaic;
leaves of plant curl
downwards and leaf size is
smaller than normal; flowers
on infected plants may be
deformed with green petals;
fruits become distorted and
are small in size; fruit is often
discolored
 Cause
 Virus
Symptoms

34. Cucumber Mosaic

35. Cucumber Mosaic

36. Squash mosaic Squash mosaic virus (SqMV)
 Symptoms vary with variety
being grown but plants can
show symptoms which
include include green
veinbanding, mottled leaves,
blisters, ring spots or
potruding veins at leaf
margins; some squash
varieties may develop leaf
enations; infected plants are
often stunted and fruits may
be malformed with mottled
skin
 Cause
 Virus
Symptoms

37. Watermelon mosaic Watermelon mosaic virus
(WMV)
 Symptoms vary widely
depending on species,
cultivar, virus strain and
environmental conditions;
symptoms on leaves may
include green mosaic
patternation, green vein-
banding, chlorotic rings
and disfigured leaves
 Cause
 Virus
Symptoms

38. Blossom-End Rot
 Blossom-end rot appears as
a dark-colored dry rot on the
end of the fruit where the
flower was. The problem is
caused by a lack of calcium in
the developing fruit. It is an
indication that calcium is
lacking in the soil or that the
plant does not have the ability
to take up enough calcium.
When growth is rapid, not
enough calcium may be
delivered to the blossom end
of the developing fruit.

39. Target leaf spot
Corynespora cassiicola
Corynespora. melonis
 Angular yellow spots appear
on older leaves; as the
disease progresses, the spots
enlarge and become circular
with light brown centers and
dark margins; as lesions
mature, they turn gray and
drop out leaving holes in the
leaves; if fruits become
infected early in their growth
then the blossom end may
darken and become
shrivelled
 Cause
 Fungus
Symptoms

40. Target Leaf Spot

41. Belly rot (Fruit rot, Damping-off)
Rhizoctonia solani
 Yellow/brown
discoloration on fruit;
water soaked spots
on side of fruit in
contact with soil;
brown mold growing
on rotting areas;
collapse of seedlings
 Cause
 Fungus
Symptoms

42. White mold
 White mold is caused by
the fungus Sclerotinia
sclerotiorum. This
pathogen infects a wide
variety of vegetable crops
including beans, carrots,
tomato, cabbage, and
lettuce. In the cucurbit
family pumpkins and some
varieties of winter squash
are most severely affected
by the disease. This
disease does not cause
leaf spots but infects both
stems and fruit.
Symptoms

43. Belly rot

44. Southern blight Sclerotium rolfsii
 Sudden wilting of leaves;
yellowing foliage; browning
stem above and below soil;
browning branches; stem
may be covered with fan-
like mycelial mat; rot on
fruit that begins on side in
contact with soil
 Cause
 Fungus
Symptoms