Major Diseases of Guava

Diseases Of Guava

1.WiltFusarium oxysporum
Economic importance:

It was first reported in 1935 from Allahabad. Area under guava cultivation in A.P was reduced to half due to the disease.
Symptoms:
 The disease can be catagorized into slow wilt and sudden wilt. In slow wilt, plant
takes several months or even a year, to wilt after the appearance of initial
symptoms and in sudden wilt, infected plant wilts in a month
 Loss of turgidity in a branch or branches of one side of the tree is the first external
symptom. Leaves in tip branch wither turn pale and droop before finally dropping
off
 Symptoms gradually appear on other branches also
 Infected and withered branches do not recover.
 A few plants may show partial wilting, which is a common symptom of wilt in
guava.
 As all the branches have withered the tree wilts and dies.
 The finer roots show black streaks, which appear prominent on removal of bark.
The roots also show rotting at the basal region and the bark is easily detachable
from the cortex.
 Light brown discoloration is noticed in vascular bundles.

Fig: Wilt in guava
Survival and spread:
Primary: Chlamydospores in soil
Secondary: Macro and micro conidia through irrigation water
Favourable conditions
 pH 6.0 is optimum for disease development. Both pH 4.0 and 8.0 reduces the
disease.
 Disease is more in loamy alluvial soils than in heavy soils
 Disease incidence increases in post monsoon period
 The nematode, Helicotylenchus dihystera aggravates the disease
Management:
Cultural
 Layers or grafts for planting in new orchards should be procured from disease
free areas
 Proper sanitation of orchard
 Wilted plants should be uprooted, burnt and a trench of 1.0-1.5m should be
dug around the tree trunk. Treat the pits with Bordeaux mixture and cover the
pit for a few days before planting new plants
 While planting damage to the root of layers or grafts should be avoided

 Maintain proper tree vigour by timely and adequate manuring, inter-culture
and irrigation
 Application of oil cakes like neem cake, mahua cake, kusum cake
supplemented with urea
 Judicious amendments of Nitrogen and Zinc
Host Plant Resistance
 Resistant varieties: Apple guava and Bhuvanagiri
 Psidium species, Psidium cattleianum var. lucidum and Syzigium cumini
(Jamun) are resistant to wilt
Biological
Aspergillus niger, Trichoderma viride, Trichoderma harzianum and Penicillium
citrinum can used as biocontrol agents
Chemical
Drench the basins of trees in orchards with disease incidence with 0.2% Benomyl or
Carbendazim, four times in a year

  1. Anthracnose/Die-back/Fruit spot/Twig blight: Gloeosporium Pisidia
    Symptoms:

Dieback phase: The plant begins to die backwards form the top of a
branch. Young shoots, leaves and fruits are readily attached, while they are still
tender. The greenish colour of the growing tip is changed to dark brown and later to
black necrotic areas extending backwards causing the die back. The fungus develops
from the infected twigs and then petiole and young leaves. These may droop down or
fall leaving the dried twigs without leaves. The disease appears in epidemic form,
during August to September.
Fruit and leaf infection phase: Fruit and leaf infection is generally seen in rainy
season crop. Pin-head spots are first seen on unripe fruits, which gradually enlarge.
Spots are dark brown in colour, sunken, circular and have minute black spots in the
centre of the lesion, which produce creamy spore masses in moist weather. Several
spots coalesce to form bigger lesions (Fig 2 &3). The infected area on unripe fruits
become corky and hardy, and often develops cracks in case of severe infection.
Unopened buds and flowers are also affected by disease which caused their shedding.
On leaves, the fungus causes necrotic lesions at the tip or on the margin. These lesions
are usually ashy grey and bear fruiting bodies.

Secondary source of inoculum: Air borne conidia

Mode of spread: spread is through the wind-borne conidia.
Epidemiology:
 The fungus is capable of growing at temperature between 20 and 25°C.
 Mycelial growth with intensive sporulation takes place at 5.5°C.
 Wounding results in quick attack by the fungus.
Management:
 Since the wound by insect predisposes the fruit to infection, spray the young
fruits after pollination with a suitable systemic insecticide (Dimethoate –
2ml/l) will take care of the infection.

 Spread of the disease can be checked by three or four spraying with Bordeaux
mixture1.0 percent or copper oxy chloride 0.2 per center.
 Summer irrigation +Nutritional management reduces the disease.

  1. Stem canker: Physalospora psidii
    Symptoms:
     Affected twigs show wilting and death.
     Cracks and lesions are formed along the stem, ar- resting translocation of
    nutrients.
     Infected fruits turn dark brown to black and dries up resulting in die-back.
     Fruit rotting takes place, blighting of leaves to enlargement
     Fungus: Physalospora psidii Stev. & Pier. Perithecia is glabrous with a fleshy
    wall.
     Ascospores are hyaline, narrow, ellipsoid and one celled.
     Conidia are single celled, ovoid with a rough wall and measure 20 to 26 x 9 to
    12 jam.
     On the stems and fruits symptoms are formed in stroma.
    Mode of spread and survival: The pathogen remains in the infected tissues beneath
    the bark and become active under favorable conditions.
    Management:
    In severe infection, the disease can be prevented by the removal and destruction of
    the infected stem.
    In mild infection, pruning of infected stem and branches is done and the cut-ends
    are painted with Bordeaux paste (1 part copper sulphate and 2 parts each of lime and
    linseed oil) or Chaubatia paste (copper carbonate – 800 g, red lead – 800 g and linseed
    oil – 1 litre).
    Spraying the trees with copper oxychloride 0.2 per cent after pruning reduces canker
    incidence.
  2. Red rust: Cephaleuros virescens
    This disease is exceptionally severe in guava.
    Symptoms:

 The alga produces specks to big patches on the leaves. They may be crowded
or
 scattered.
 The pathogen extends between cuticle and epidermis and penetrates the
epidermal cells.
 Fruit infection by alga is not common on fruits. Fruit lesions are usually
smaller than leaf spots.
 They are dark green to brown or black in colour.
Primary source of inoculum: Dormant mycelia
Secondary source of inoculum: Zoospores

Mode of spread and survival:

 The disease is more common on closely planted mother plants. The zoospores
cause the initial infection.
 High moist condition favours the development of fruiting bodies of the algae.
Management:This algal disease is controlled by spraying with Bordeaux mixture 1.0 Perr cent or copper oxychloride 0.3 per cent.

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