Plant diseases

1. Dr. Hanumantappa B Nayaka
M.Sc., M.Phil., PhD., PDF(Spain)., MIScT (U K)
Asst. Professor
Department of Life Sciences
Kristu Jayanti College Autonomous
Bengaluru-77, Karnataka
Plant Pathogens

2. Introduction
• Diseases and pests represent a major threat to the commercial
production of grapes in the world.
• Climatic conditions are conducive to the development of several
major grape diseases, including black rot, downy and powdery
mildew.
• Each of these diseases has the potential to destroy the entire
crop.
• Most diseases occur simultaneously within the same vineyard
during the growing season.

3. Downy Mildew
Causal organism
Scientific Name: Plasmopara viticola
Symptoms
Leaves
• Roughly circular yellowish discolourations called “oil
spots”.
• White fluffy growth primarily on the lower leaf surface.
• As lesions age, they turn brown from the centre outward.
• Severely infected leaves may drop.
Small, circular lesions on
upper side of leaf
Downey mildew growth
on under side of leaf

4. Shoots
• Infected shoot tips curl and covered with white fluffy sporulation.
Berries
• White fluffy sporulation on small berries.
• May shrivel and drop off.
• Stay hard when healthy berries start to soften at veraison.
Downey mildew growth on
berries
Severely infected berries
Courtesy:
www. Ohioline. osu. edu

5. Biology
• The causal fungus, Plasmopara viticola overwinters as thick-
walled oospores in infected tissues and in the soil.
• A minimum of 10 mm of rain is required for oospores to
produce sporangia that are dispersed by rain splash to young
green tissue.
• The sporangia release motile zoospores that swim to the
stomates, germinate and infect tissues.
• Disease development is most rapid between 20oC and 25oC
with frequent rain or dew.

6. Powdery mildew
Causal organism
Scientific Name : Erysiphe necator (previously Uncinula necator)
Losses in yield of fruits may be upto 40-60%. In addition to loss of yield,
infected berries tend to be higher in acid content than healthy fruits and are
unsuitable for wine making.
Symptoms:
On all tissues, powdery mildew looks like a greyish-white powder.
Leaves
• Frequently first found on the undersides of leaves.
• Lesions become apparent on the upper sides of leaves as well.
• On rapidly growing leaves, infections on the underside may cause the leaves to
appear puckered on top.

7. • Severely infected leaves may become brittle and drop off.
• Starting as early as late July, very small orange then brown and eventually
black spherical structures cleistothecia develop on the upper and lower
surfaces of infected leaves.
Shoots
• Initially greyish-white, develop into brown irregular blotches.
• Indistinct margins and remain visible after shoot hardening.
Berries
• Become covered in conidia.
• An initial floury appearance that later becomes dark and grey.
• Dry out and may drop off.
• Later infections (3-4 weeks post bloom) will have superficial greyish
scarring.

8. Severe powdery mildew on berries
Powdery mildew on upper side of leaves
Severe powdery mildew on cane
Powdery mildew on under side of leaves
Courtesy: www.oardc.ohio/grapeipm

9. Black rot
Causal organism
Scientific Name: Guignardia bidwellii
Symptoms
Leaves
• Relatively small, brown circular lesions develop on infected leaves and within
a few days tiny black spherical fruiting bodies (pycnidia) protrude from them.
Berries:
• Infected berries first appear light or chocolate brown but quickly turn darker
brown, with masses of black pycnidia developing on the surface.
• Finally, infected berries shrivel and turn into hard black raisin-like bodies that
are called mummies.
Shoots
• under high disease pressure brown to black elongated lesions develop.

10. Black rot lesions on leaves
Mummified berries
Infected berry with black
pycnidia
Black rot berries in
cluster
Tiny black pycnidia
on leaf lesion
Elongated lesions
on petiole
Courtesy:
PHOTO BY R. PEARSON

11. Anthracnose/Birds eye disease
Causal organism
Scientific Name: Elsinoe ampelina
• It is especially serious on new sprouts during rainy season.
• Among various foliar diseases of grapevine in India, anthracnose has
longest spell spread over the period from June to October
Symptoms
Leaves
• Initially pin-prick dark spots.
• Developing into small round spots with brown or black margins with
greyish-white centres which drop out causing a ‘shot-hole’ appearance.
• Severe infections cause malformed leaves that shrivel up and drop.

12. Shoots
• Deep elongated cankers
• Greyish in the centre with a raised dark reddish brown to violet-black edge
• Infected shoots crack and become brittle
Berries
• Reddish circular spots becoming violet with a greyish centre and a raised
black edge “bird’s eye rot”
• Lesions can extend into the pulp, causing cracking and opening the berry to
secondary infections
• Severely infected berries dry up and drop prematurely.

13. Sunken lesions on shoots Anthracnose on berry
Birds eye rot symptoms on berry
Courtesy:
www.oardc.ohio/grapeipm

14. Fusarium Wilt
Causal organism
Scientific Name: Fusarium oxysporum
Symptoms:
• Shoots and leaves wilt and die in mid-season, with characteristic
brown-red discolouration of the vascular tissue of the affected areas.
• Leaves drop prematurely and clusters fail to develop and shrivel to
mummies. Symptoms range from one or two shoots on a vine to
whole plant collapse.

15. Management
• Collect and burn fallen leaves and twigs.
• Sanitation of the orchard is highly essential.
• Clean cultivation of vines or removal and destruction of all diseased parts.
• Vine should be kept high above ground to allow circulation of air by proper
Spacing
• Grow resistant varieties like Chholth Red, Chholth white, Skibba Red
(Powdery mildew), Amber Queen,Dogridge, Red Sultana (Downey mildew)
and Banglore blue, Golden muscat, Golden queen (Anthracnose).
• Prophylactic spray with B.M. 1% or Lime sulphur at dormant stage delays
development of disease by decrease PM initial inoculum.
• Spraying Bordeaux mixture 1% or COC@ 0.2% or carbendazim @0.1%.

16. Lets sum up
❖Downey mildew pathogen causes irregular, yellowish, translucent spots on the
upper surface of the leaves and white fluffy sporulation on small berries.
❖On all tissues, powdery mildew looks like a greyish-white powder
❖Due to black rot, infected berries shrivel and turn into hard black raisin-like
bodies that are called mummies.
❖Anthracnose affected berries shows ‘shot-hole’ appearance.
❖Pruning practices, trellis designs and vineyard lay outs that maximise air
movement and light penetration within vine canopies discourage disease
development. However, on susceptible varieties, fungicide spray programmes are
required in most seasons to prevent crop loss.

17. Thank you