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PLANT DISEASES

Submitted BY,Keerthy.V.S Natural ScienceRoll No: 62

DISEASES OF COCONUT TREE1) LETHAL YELLOWING

SymptomsPremature 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

ManagementThe 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

2) C0C0NUT SCALE

SymptomsPale 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

CauseInsect

ManagementMay be possible to control coconut scale by pruning infested parts of trees and destroying by burning; chemical control may be necessary

3)STEM BLEEDING DISEASE

SymptomsSoft, 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

CauseFungus

ManagementAvoid 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

4)BUD ROT AND NUTFALL

SymptomsChlorosis 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

CauseOomycete

ManagementControl 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

DISEASES OF PEPPER1)FOOT ROT DISEASE

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.

Symptoms• 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 wiltsfollowed by shedding of leaves and spikes with or without black spots. The branchesbreak up at nodes and the entire vine collapses within a month.

2) POLLU DISEASEThis 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%)

3)STUNT DISEASESYMPTOMSThe vines exhibit shortening of internodes to varying degrees. The leaves becomesmall 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.

DISEASES OF PADDY1)SHEATH BLIGHT

SymptomsCircular, 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

CauseFungus

ManagementAvoid 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

2)RICE BLASTSymptomsLesions 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

CauseFungus

ManagementIf 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

3)STEM BORERS

SymptomsLongitudinal 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

CauseInsect

ManagementStem 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

DISEASES OF ARECANUTDRY MAHALIPathogenFruit rot of arecanut is caused by the fungusPhytophthora meadii. P. arecae and P. heveae werealso reported to be involved in the disease. Bud rotand crown rot diseases caused by the same fungusoccur either as a further manifestation of the fruit rotinfection or independently as fresh infection duringthe monsoon and subsequent cooler months. Thefungus survives as oospores, chlamydospores andmycelium in soil, on fallen nuts, on dried nuts and oninflorescence remaining in the crown.Symptoms• Characteristic symptom is rotting and extensiveshedding of the immature nuts which lie scatterednear the base of the tree.• Initial symptoms appear as dark green/ yellowishwater-soaked lesions on the nut surface near theperianth (calyx).• The infected nuts lose their natural green lusture,quality and hence have a low market value.

• 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’

DISEASES OF RUBBER

SymptomThe 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 ofaffected branches dry and dried leaves remain on these branches.

ControlIn 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.

1)PINK DISEASE

SymptomsDuring 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.

ControlThe 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.

2)BARK ROT

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.

CONCLUSION

* Disease of vegetables crops. Third Edition R.S SINGH. * Introduction to principles of pathology. R.S SINGH.

REFERENCE

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