Powdery mildew on Pea, Cucurbits, Wheat and Apple and its Management

Powdery mildew of pea:

  • Most wide spread and easily recognized plant disease
  • Much more serious than downy mildew and worst in dry weather
  • In 100% infected crop, loss in pod no. is 21-31% and reduction in pod weight is 24-27%

Host range: bean, Lucerne, coriander, turnip, cabbage

Casual organism : Erisiphe pisi syn E. polygoni

  • Mycelium ectophytic, the entire thallus except the haustoria
  • Conidiophores- septate, not much different in shape to conidia, bear conidia in chain
  • Conidia- hyaline, elliptical, bassel shaped, cylindrical, unicellular

Symptoms of Powdery mildew on Pea:

  • A white powdery substance appears on the leaves at the flowering
  • More patches on both sides of the leaves and later on tendrils, pods and
  • In advance stage of disease, it may cover all aerial parts with white floury
  • Consist mycelium and
  • Affected plant part
  • Physiology of host affected i.e. increase transpiration and respiration and decrease photosynthesis.
  • Ultimately the infected pod may be shriveled and produce small

Disease cycle of Powdery mildew on Pea:

  • Soil borne disease
  • Primary inoculum: perithecia/ cleistothecia living in soil
  • Cleistothecia are formed at the later stages of plant and on crop debris after conditioning by soil temperature and moisture
  • After disintegration of cleistothecia, the ascospores infect lower leaves
  • The fungus grows, produces conidia and starts secondary cycle
  • Seed survival

Epidemiology of Powdery mildew on Pea :

Disease is more severe during dry season than in wet season .Conidia germinate at temperature 20-240c. Under favorable condition, conidia germinate within 1 hour and an entire leaf may colonize within 150 hours. RH is not so important.

Management of Powdery mildew on Pea :

  • Burn all plant debris and destroy alternate host
  • Early sowing varieties sustain less damage as disease appears late in the season. E.g. L- 116
  • Apply sprinkle irrigation- washes the conidia
  • Crop rotation 3-4 years with cereals, sugarcane, gram,
  • Use of resistant varieties. E.g. Rachana, PM-2
  • Chemical spray of sulfur or wettable sulfur compound @3 gm/ltr at 10-15 days interval
  • Sulfur dust 25 kg/hac or karathene(0.2%)

Powdery mildew of cucurbits:

  • Serious in pumpkin, cucurbits, bottle gourd

Etiology:

Erysiphe cichoracearum (found in cooler months, spring or early summer)

Podosphaera xanthii, previously known as Sphaerotheca fuligena and S. fusca (found in warmer months)

  • Main identification of these conidia is fibrosin bodies in conidia of xanthii
  • Both pathogen have septate, hyaline, uninucleate, superficial (ectophytic) hyphae

Symptoms of Powdery mildew of cucurbits :

  • Disease appears as white powdery coating over the leaves and stems of
  • First symptoms are tiny, white to dirty grey spots
  • Spots enlarge to show powdery masses over the entire leaves and also in green stems
  • Development of necrotic areas make leaves lose their green appearance and become pale and dry and withers
  • The leaves become distorted, fruit yields is very much

Disease cycle of Powdery mildew of cucurbits:

Pathogen perennates as cleistothecia over wintering i.e. primary source of inoculums. On availability of suitable host ascospore germinate which are released from ascus that are lined inside cleistothecia and cause primary infection.Completes in 3-7 days

  • Mycelium survive in either cucurbits
  • Alternate host:
    • xanthii: bean, brinjal, okra
    • cichorocearum: castor, mango
  • Secondary inoculums: air borne conidia

Epidemiology:

Disease development is favored at temperature 10-320c, mean 260c, with low to preferably high RH

Management of Powdery mildew of cucurbits :

  • Destroy the crop debris,Removal of collateral, alternate host
  • Early sowing
  • Resistant variety
  • Biological control : Ampelomyces quisqualis, Tilletiopsis minor hyperparasite against powdery
  • Spray karathene 05-0.2%

Powdery mildew of wheat:

  • More serious in hilly areas but is appearing in the terai particularly in irrigated wheat fields
  • Also attack barley, rye, oats and grasses

Casual organism : Erysiphe graminis, Blumeria graminis sp. tritici

Symptoms Powdery mildew of wheat :

  • Disease mostly appear from jointing to flag leaf stage
  • White to grey fungal growth on leaves, stems, heads and glumes

The leaf tissue opposite from the white mould growth becomes yellow, turning tan or brown.

  • Later cleistothecia are visible as black dots
  • Plants stunted, size of leaf reduced

Disease cycle and epidemiology:

  • Cleistothecia, conidia and mycelium surviving on the wheat straw will initiate the disease on the plant
  • Germ tube will directly penetrate the host epidermis to establish the haustoria and they grow superficially
  • Secondary inoculums: airborne conidia
  • Optimum temperature 15-220c and RH 100%

Management Powdery mildew of wheat:

  • Destroy crop debris to kill fungus
  • Alternate host removal
  • Avoid high nitrogen application, more tiller formation and dense strands increase susceptibility
  • Scouting of field regularly
  • Avoid above two leaves infection so that grain formation is not harmed
  • Karathene spray 1%
  • Seed treatment with bayleton or spray

Powdery mildew of apple:

  • Also affects in pear
  • Firstly discovered in Kashmir in 1931 by Butler and Bisby and later in U.S, Japan and Australia
  • Only fungal disease that cause without wetting from rain
  • Nursery plants attacked more than the older

Casual organism : Podosphaera leucotricha

      • Heterothallic fungus
      • Obligate parasite, ectophytic mycelium, sends saccate or lobed haustoria

Symptoms:

  • Firstly the disease appears on leaves, twigs, flowers and fruits
  • Small greyish or whitish patches of fungus growth are seen on the underside of the leaves which soon curl and then become folded
  • Affected leaf grow longer and narrower than normal leaves with curled margin
  • Infected leaves become hard, brittle and often crack
  • Tree may not bear flower at
  • Infected bud die, fruits reduced in size and surface may show effect of fungus
  • Fruit skin crack and permit secondary fungus to attack and cause early decay

Disease cycle and epidemiology :

Fungus overwinters in the form of resting mycelium or encapsulated haustoria in the vegetative buds. In spring season, at bud stage, fungus become active. Primary inoculums: cleistothecia, ascospore (sexual spore) infect lower leaf. Air borne conidia serve as secondary inoculums

  • Temperature, humidity and light play significant
  • Rainfall decrease the intensity of
  • Conidia germinate 22-250c, mycelium grow at 200c, above 330c fatal
  • Conidia do not germinate below 88.5% RH

Management:

  • Removal of affected buds, twigs, shoots and leaves
  • Use of resistant varieties like Golden Chinese, Maharaja Chunth
  • Botanical extract like neem
  • Karathene 0.1%, sulfur containing fungicides at 15 days interval
  • Carbendazim 0.5% spray at four different stages:
    • Dormant bud stage
    • Petal fall stage
    • Full development
    • Bud swell stage

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