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Diseases
Abnormal leaf fall
Causative agent: Phytophthora meadii McRae.
Symptoms: First
the fruits rot, later infected leaves fall in large numbers prematurely, either
green or after turning coppery red. A black lesion may develop on the petiole with
a drop of latex, often coagulated, in the centre. Lesion may develop on the midrib
and leaf blades also. Heavy defoliation may lead to considerable loss of crop and
die-back of terminal twigs.
Management: Prophylactic
spraying of the foliage prior to the onset of south west monsoon with (1) 1% Bordeaux
mixture (3000 - 4000 l/ha) using high volume sprayers or (2) Oil-based copper oxychloride
dispersed in diluent spray oil employing either low volume airblast sprayers from
the ground or through aerial application. For aerial spraying, 6.2 litres of 40%
oil based copper oxychloride paste in 37 litres of diluent oil or 8 kg oil dispersible
copper oxychloride powder 56% in 40 litres of oil is used per hectare. Spraying
should be done as close to the monsoon as possible.
Shoot rot
Causative agent:
Phytophthora palmivora (Butl.) Butl and P. meadii Mc Rae
Symptoms:
The tender green shoots rot. This is more damaging for nursery seedlings
and the young plants in the field.
Management : For
mature plants, prophylactic spraying is given, as in the case of abnormal leaf fall.
For young plants in the nursery as well as in the field, spraying with copper fungicides
before the onset of south west monsoon coupled with repeated spray rounds during
bright breaks protect the plants. For ensuring proper sticking of the spray on tender
foliage, sticker (Sandovit, Tenac, Teepol, Triton AE etc) may be added at the rate
of 0.5 ml/litre of spray fluid.
Powdery mildew
Causative agent:Oidium
heveae Steinm.
Symptoms: Tender
leaves with ashy coating curl, crinkle, and edges roll inwards and fall, leaving
the petioles attached to the twigs like a broom-stick. After a few days, the petioles
also fall. Die-back of twigs follows. On older leaves, white patches later causing
necrotic spots reduce photosynthetic efficiency. Infected flowers and tender fruits
are shed, affecting seed production.
Management: For
young plants spray carbendazim (0.05%) or wettable sulphur (2g/l) at fortightly
interval. Dusting during the
refoliation period commencing from bud break in about 10% of the trees, giving 3
to 5 rounds at weekly to fortnightly interval using 11 to 13 kg 325-mesh fine sulphur
dust per round per hectare. Sulphur mixed with an inert material like talc (70:30)
is commonly used. 0.2% Wettable sulphur (1 kg in 400 litres of water) is also effective
in nurseries and for young plants as a spray. Bavistin 0.05% a.i. (1g in 1 litre
water) spraying is more effective than sulphur for nurseries and young rubber. Alternate
use of bavistin and sulphur is recommended to avoid resistance problem.
Bird’s eye spot
Causative agent:
Drechslera heveae (Petch) M.B. Ellis
Symptoms: Symptoms
appear as small necrotic spots with dark/brown margins and pale centre. Severe infection
leads to premature defoliation and die back.
Management: Give
repeated spraying with Bordeaux mixture 1% or Dithane M-45 0.2% or Bavistin 0.02%.
Shading the nursery plants reduces the disease incidence. Maintain seedlings in
vigorous condition through adequate balanced nutrition.
Leaf Spot
Causative Agent:
Corynespora cassiicola (Berk & Curt)
Symptoms: Large
spots, with brown margins and pale centre is the common symptom. The centre may
fall off forming shot holes. On mature trees light green leaves during refoliation
are more susceptible. Several lesions coalesce to form large blighted area. Disease
spreads along the veins leading to a brownish “railway track” or "fish
bone" like appearance. Even a localized infection on midrib or base of a leaf
causes leaf abscission. Defoliation leads to die-back of branches.
Management: Repeated
spraying with Bordeaux mixture 1% or dithane M-45 0.2% or bavistin 0.02% is recommended
for nursery. Shading the nursery reduces the disease incidence. Maintain seedlings
in vigorous condition through adequate balanced nutrition. High volume spraying
with mancozeb (dithane/Indofil M-45) 0.2% or carbendazim (bavistin) 0.05% at 2-3
weeks interval during refoliation is effective in mature plantation. Micron spraying
with oil dispersible copper oxychloride 56% (8 kg) or oil dispersible mancozeb 70%
(7 kg) dispersed in 40 litre spray oil per ha is also effective.
Pink disease
Causative agent:
Corticium salmonicolor Berk & Br.
Symptoms: It is
more damaging for plants in the age group of 2 to 12 years. The main seat of infection
is usually the fork region. White or pink coloured cobweb mycelial growth occurs
on the bark surface with streaks of latex oozing out from the lesions. Rotting,
drying up and cracking of the affected bark will follow. Sprouts develop from below
the affected portion. The distal portion of branches dry and dried leaves stick
to the dead branches.
Management
Prophylactic: Spraying
two rounds of 1% Bordeaux mixture (during May and August) on to the fork and branches
reduces disease incidence. For 2-year-old plants, the topmost brown portion has
to be applied with Bordeaux paste in a 30 cm wide band all around. The forking region
also has to be applied with the paste. In leaning plants, in addition, a 30 cm wide
band on the convex side of the bend has to be applied. In 3 years old plants, application
has to be made on all major forking regions except the lowermost one and also on
all the leaders of the topmost brown regions.
Curative: Follow
frequent tree inspection during June to October for detecting infection and application
of Bordeaux paste in early stage on infected part and up to 30 cm above and below.
In advanced cases, Bordeaux paste may be initially applied and then the affected
portion scraped to remove mycelium and decayed bark, followed by a second Bordeaux
paste application. Dried branches should be pruned after disinfection. Thiride (TMTD)
(10 g in 1 kg) incorporated in a wound dressing compound like rubberkote, sopkote
etc or tridemorph (calixin) 2% in 1% ammoniated field latex or thiride 0.75% or
tridemorph 1% or propiconazole (tilt) 0.1% in pidyvyl, china clay and water (1:2:4
by volume) is also effective as rainwash is prevented. Tridemorph (2 per cent) incorporated
in 1 per cent ammoniated field latex is also effective.
Patch canker or bark canker
Causative agent: Phytophthora palmivora, Phytophthora meadii, Pythium
vexans
Symptoms:
On the tapping panel region or anywhere on the stem including the collar
region, and occasionally on the roots, swelling and bark burst occur with amber-coloured
liquid oozing out. This may not be evident in all cases. In most cases oozing of
latex is observed. The bark rots, and a coagulated rubber pad, emanating a foul
smell is seen in between the wood and the rotting bark. When this is removed slight
discolouration of the wood in this region is also noticed.
Management: The
affected region may be scraped to remove all the rotting bark and the coagulated
rubber and the wound washed well with Dithane (Indofil) M45, 0.75% (10 g per litre
of water). When the fungicide dries up, apply wound dressing compound.
Black stripe, black thread or black rot
Causative agent:
Phytophthora palmivora, P. meadii
Symptoms: In the
renewed bark region, small depressions are formed due to localized rotting and drying
of bark, which gets pressed to the wood. When scraped, deep vertical black lines
running downward into the tapping bark and upwards into the renewed bark are noticed.
Bark rot often reduces yield. The renewed bark becomes highly uneven.
Management:
If tapping is regularly done during rainy season, the tapping panel should
be disinfected at weekly intervals by brushing with Dithane (Indofil) M45, 0.375%
a.i. (5 g per litre of water). Phosphorous acid 0.08% at weekly intervals is also
effective. In the infected cases, scrape off the affected tissues and apply the
fungicide. When the fungicide dries up, a wound-dressing compound may be applied.
Dry rot, stump rot, collar rot or charcoal rot
Causative agent:
Ustulina deusta (Hoffm.ex Fr) Lind.
Symptoms: It affects
roots, collar, trunk and branches with copious exudation of latex from the lesions.
Affected bark and wood become soft and powdery with double black lines in the wood.
Grey, crust-like flat fructifications, which later coalesce and turn black are seen
on the bark. Affected trees or branches are killed or blown over. Ustulina root
infections are also noticed.
Management: Scrape
off the fructifications, affected bark and wood showing black lines. Apply a wound
dressing compound in which Thiride 0.75% a.i is incorporated. Hexaconazole 0.02%
a.i (Contaf) is also effective. Avoid accumulation of rubber at the base of the
tree. For root infection, see the treatment for brown root disease.
Brown root disease
Causative agent:
Phellinus noxius Corner G.H. Cunn
Symptoms: Retardation
in growth and a general yellowish discolouration of the foliage occur. Affected
roots when examined show a thick encrustation of soil, sand and fungal hyphae cemented
to the root and brown lines in the affected roots. In advanced cases, the plants
dry up.
Management:
Completely killed and dried roots may be traced, pruned off and burnt along
with any rotting stump in the immediate vicinity and partially affected and healthy
roots washed with calixin 1% or tilt 1% solution (provisional recommendation). When
the fungicide dries up, a thin coating with a wound dressing compound may be given.
Refill the soil and drench the base with fungicide solution. The dried up plants
may be uprooted, root traced, collected and destroyed. As prophylactic measure the
bases of trees neighbouring the affected trees may also be drenched with calixin
1% or tilt 1% solution. Drench the nursery beds having affected plants with any
of the above mentioned fungicide solution.
Poria root disease
Causative agent:
Poria vincta (Berk.) Cooke
Symptoms: Yellow
discolouration of leaves is the only external symptom. The affected root shows soil
encrustation as in the case of brown root disease but to a limited extent. Around
the root, fungus forms a complete mat, pale white in colour intermingled with brick
red and black tinges.
Management: Completely
killed and dried roots may be traced, pruned off and burnt along with any rotting
stump in the immediate vicinity and partially affected and healthy roots washed
with calixin 1% or tilt 1% solution (provisional recommendation). When the fungicide
dried up, a thin coating with a wound dressing compound may be given. Refill the
soil and drench the base with fungicide solution. The dried up plants may be uprooted,
root traced, collected and destroyed. As prophylactic measure, the bases of trees
neighbouring the affected trees may also be drenched with calixin 1% or tilt 1%
solution. Drench the nursery beds having affected plants with any of the above mentioned
fungicide solution.
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