4. Premature dropping of fruit; fruit with brown-black water-soaked
appearance; necrosis of inflorescences; flower
stalks turn black; lower, older leaves turning yellow; entire
crown turning yellow; yellow leaves turn brown, dry out and
hang from canopy
The most effective method of managing the disease is to
plant resistant coconut varieties such as Malayan dwarf or
Maypan; antibiotic treatment is effective but not usually
practical for large scale plantings
5. Pale yellow spots on leaves; entire leaves
yellowing; leaves turning brown and
dropping prematurely; adult insect is a
flattened oval, resembling a scale, which is
red-brown in color
Insect
May be possible to control coconut scale by pruning infested parts of trees
and destroying by burning; chemical control may be necessary
6. Soft, yellow rot on trunk; affected areas are dark and turn black as they
mature; a reddish-brown liquid may ooze from rotting regions and spill
down trunk
Fungus
Avoid wounding palms with machinery and tools to reduce disease
incidence; disease can be controlled with applications of the fungicide
benomyl where registered; infected trees should be removed and destroyed
as soon as possible
7. Chlorosis of youngest open leaves; leaves rapidly turning necrotic; necrotic
spots on leaf bases; unopened spear leaves can be pulled away from the
plant easily; removal of unopened spear leaves reveals soft, pink-red tissue
with foul smell; leaf necrosis spreading through central crown leaves; woody
parts of plant may have water-soaked, pink lesions with dark borders; infected
inflorescences abort nuts
Oomycete
Control of the disease is reliant on good sanitation practices and the use of
appropriate systemic fungicides; remove all infected debris and dead trees
from plantation and destroy; irrigate trees early in the day to allow surfaces to
dry off during the day
8. Foot rot (quick wilt disease) caused by Phytophthora capsici is the most destructive
of all diseases and occurs mainly during the south west monsoon season. All parts of
the vine are vulnerable to the disease and the expression of symptoms depend upon
the site or plant part infected and the extent of damage.
• One or more black spots appear on the leaves which have characteristic fine
fimbriate margins which rapidly enlarge and cause defoliation.
• The tender leaves and succulent shoot tips of freshly emerging runner shoots
trailing on the soil turn black when infected. The disease spreads to the entire vine
from these infected runner shoots and leaves during intermittent showers due to
rain splash.
• If the main stem at the ground level or the collar is damaged, the entire vine wilts
followed by shedding of leaves and spikes with or without black spots. The branches
break up at nodes and the entire vine collapses within a month.
9. This disease is caused by Colletotrichum gloeosporioides. It can be distinguished
from the pollu(hollow berry) caused by the beetle by the presence of characteristic
cracks on the infectedberries. The disease appears towards the end of the monsoon.
The affected berries showbrown sunken patches during early stages and their
further development is affected. In laterstages, the discolouration gradually
increases and the berries show the characteristic crosssplitting. Finally, the berries
turn black and dry. The fungus also causes angular to irregularbrownish lesions
with a chlorotic halo on the leaves. The disease can be managed byprophylactic
spraying of bordeaux mixture (1%) or carbendazim + mancozeb (0.1%)
The vines exhibit shortening of internodes to varying degrees. The leaves become
small and narrow with varying degrees of deformation andappearleathery,puckered
andcrinkled. Chlorotic spots and streaks also appear on the leaves occasionally. The
yield of theaffected vines decreases gradually.Two viruses namely Cucumber mosaic
virus and a Badnavirus are associated with the disease.
10. Circular, oblong or elliptical, green to gray water-soaked spots
on leaf sheaths; lesions with pale green or white center and
purple-brown margin; lesions covering leaf sheaths and stems;
poorly filled grains
Fungus
Avoid overfertilizing plants as excessive nitrogen application has been shown to
increase susceptibility to the disease; applications of foliar fungicides may be required;
two applications are recommended and should be timed so that the first application is
made between the early internode elongation and the second application made on
emerging panicles 10-14 days later
11. Lesions on all parts of shoot; white to green or gray
diamond-shaped lesions with dark green borders; death
of leaf blades; black necrotic patches on culm; rotting
panicles
Fungus
If disease is not endemic to the region, blast can be controlled by planting resistant
rice varieties; avoid over-fertilizing crop with nitrogen as this increases the plant's
susceptibility to the disease; utilize good water management to ensure plants do
not suffer from drought stress; disease can be effectively controlled by the
application of appropriate systemic fungicides, where available
12. Longitudinal white patches on leaf sheaths; central leaf whorl drying out and
turning brown; tillers drying out without producing panicles; panicles may dry out
or may produce no grain; adult insects are nocturnal moths which lay their eggs
on the leaves or leaf sheaths of the rice plants; larvae are legless grubs which
feed on leaf sheaths before entering the stem of the pant
Insect
Stem borers are difficult to control with insecticides as once they bore inside the
stem they are protected from chemical sprays; in order for chemical control to be
successful, repeated applications of appropriate insecticide must be made to the
foliage; granular formulations give better control than sprays; clipping seedling
prior to transplanting can successfully reduce moth numbers as eggs are laid at
leaf tips; harvesting plants at ground level can remove the majority of larvae from
the field
13. Pathogen
Fruit rot of arecanut is caused by the fungus
Phytophthora meadii. P. arecae and P. heveae were
also reported to be involved in the disease. Bud rot
and crown rot diseases caused by the same fungus
occur either as a further manifestation of the fruit rot
infection or independently as fresh infection during
the monsoon and subsequent cooler months. The
fungus survives as oospores, chlamydospores and
mycelium in soil, on fallen nuts, on dried nuts and on
inflorescence remaining in the crown.
Symptoms
• Characteristic symptom is rotting and extensive
shedding of the immature nuts which lie scattered
near the base of the tree.
• Initial symptoms appear as dark green/ yellowish
water-soaked lesions on the nut surface near the
perianth (calyx).
• The infected nuts lose their natural green lusture,
quality and hence have a low market value.
14. • The lesions on the fruits gradually spread coveringthe whole surface before
or after shedding whichconsequently rot.
• White mycelial mass envelopes on entire surfaceof the fallen nuts.
• As the disease advances the fruit stalks and theaxis of the inflorescence rot
and dry, sometimesbeing covered with white mycelial mats.
• Infected nuts are lighter in weight and possesslarge vacuoles
• Infection occurring later in the season results inrotting and drying up of nuts
without sheddingcalled ‘Dry Mahali’
15.
16. The seat of infection is usually at the fork region. white or pink coloured
cobweb mycelial growth form on the surface of the bark with streaks of
latex oozing out from the lesion resulting in rotting, drying up and cracking
up of the affected bark.The distal portions of
affected branches dry and dried leaves remain on these branches.
In high disease prone areas,the highly susceptible clones can be treated as
a prophylactic measure with Bordeaux mixture or Boreaux past.In the
early stages of infection,apply Bordeaux past up 30(m above the below
the affected region. Tridemorph (1%) or Thiram (0.75%) in pidivyl, china
clay and water mixed in the proportion 1:2:4 by volume is very effective
for control.Thiram (0.75%) mixed in petroleum wound-dressing
compounds like rubberkote, sopkote etc. is also effective.
17. During rainy season when trees are tapped depression are formed in the tapping
panel due to localized rotting and drying of bark. Black vertical lines running down
ward in to the tapping bark and upwards in to the renewed bark are noticed. The
bark when renewed becomes highly uneven.
The tapping cut and near by bark should be washed by with Mancozeb (0.375%)
or phosphorous acid (0.08%) at weekly intervals. The rotten bark may be scraped
off and applied with fungicide and then covered with petroleum wound-dressing.
18. CONCLUSION
DISEASES OF PLANTS, DEVIATIONS FROM THE NORMAL
GROWTH AND DEVELOPMENT OF PLANTS INCITED BY
MICROORGANISMS, PARASITIC FLOWERING PLANTS,
NEMATODES, VIRUSES, OR ADVERSE ENVIRONMENTAL
CONDITIONS. INJURIES TO PLANT LIFE DUE PRIMARILY TO
INSECTS, MITES, OR ANIMALS OTHER THAN NEMATODES
ARE NOT REGARDED AS PLANT DISEASES.
19. REFERENCE
* Disease of vegetables crops.
Third Edition
R.S SINGH.
* Introduction to principles of pathology.
R.S SINGH.
