Post harvest diseases of garlic
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White rot - Sclerotium cepivorum
Blue mold rot - Penicillium spp.
Black mould - Aspergillus niger
Pink rot - Pyrenochaeta terrestis
Internal bulb rot - Macrophomina phaseolina
Basal rot - Fusarium oxysporum f. sp. garlic
Neck rot - Botrytis allii
White rot - Sclerotium cepivorum,
s. rolfsii
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Leaves decay at the base, turn yellow, wilt, and topple over
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Roots and bulbs - covered with a fluffy white mycelium
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Affected bulbs may become watery, and the outer scales crack as
the bulb dries and shrinks
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Small black sclerotia form on and in affected bulb parts
Mode of spread and survival
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Cool weather - needed for germination of sclerotia and hyphal
growth
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Mycelium - encounters a host root, the fungus will form appresoria
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Mycelium can grow outwards from the roots of one plant to the roots
of a adjacent plant
Control
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Rotating out of Allium crops for ten years
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Destroying infected tissue
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Planting disease - free seed stock
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Seed dressing with benomyl or carbendazim(100-150g/kg of seed)
Micro sclerotia of the White Rot fungus
S.cepivorum developing on an infected
garlic bulb
Basal rot - Fusarium oxysporum f. sp. garlic
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Plants - show reduced emergence, yellowing and/or browning
(necrosis) of leaves beginning at tips
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Reduced bulb size, bulb decay, and brown, poorly developed root
systems
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In storage - bulbs show spongy, sunken, yellow brown rotting
lesions
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In early stages - infected bulbs are softened, brown and watery
when cut open
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White, light pink or reddish fungal growth covering the cloves or in
rot cavities
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Deep cracks form in the cloves, followed by break down of the
tissue, which will eventually dry down to a portion of its original size,
the cloves becoming crinkled and small
Disease Cycle
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Soil borne fungus and can persist for long periods in the soil
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Transmission - infested soil on tools or equipment, infected debris,
infected seed, or run-off water
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Pathogen enters the plant through wounded tissue
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Disease develops from the base of the bulb and progresses towards
the tips of the cloves
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Favored by higher RH and temperatures(20-30oC)
Management
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Avoid rotations with Allium spp.(e.g. onions and leeks) and cereals
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Store bulbs at cool temperatures and low humidity with good
ventilation
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Avoid storing damaged bulbs
Blue mold rot - Penicillium spp.
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A blue-green color powdery mould is observed on cloves in soil and
in storage, thus its common name, “Blue Mold”
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Air-borne spores spread the disease
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Infection first occurs on wounds sustained when cloves are
separated from the parent bulb
CONTROL
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Bulbs are harvested carefully to avoid wounds and bruising, then
promptly dried or cured
Black mould (Aspergillus niger and A. alliaceous)
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Whole tissue become black powdery
mass
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Individual bulbs shrivel and become light
in weight
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Under high humid condition the inner
tissues become moderately soft
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Infected bulbs lose their pungency and
smell
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Rotten garlic cloves show black, brown,
pink or white coloured rotting
Fungus
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Mycelium - branched, septate thick walled foot cells differentiate and
give rise to a single conidiophore
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Conidiophore - globose on which brown sterigmata are formed
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Vesicle, sterigmata, conidia make up the black head - characteristic
of the fungus
Control
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Rapid and thorough curing
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Storage - good ventilation
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Temp - just above 0oc
Pink rot
Pyrenochaeta terrestis
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Roots are affected and they turn pink or reddish and sometimes
darken to a red or purple colour
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Black spores form on the diseased roots which eventually shrivel
and die
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Pathogen - Soil borne and infection is mostly from mycelia in the soil
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Temp - 24-28oc
Internal bulb rot - Macrophomina phaseolina
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No external symptom can be observed unless the outer scales are
removed
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Black pin head microsclerotia develop over the fleshy scales which
are light in weight, brown, mostly shrivelled
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Do not lose their pungency
Control
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Dipping of bulbs in formalin 0.03%
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Boric acid-2.0%
After harvest to minimize
storage rot
Neck rot - Botrytis allii
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Found upon the bulbs at the time of harvest
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Affected scale tissue become soft
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Dense layer of grey mould appear at the neck
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Infection progresses most rapidly down the scales which have been
originally infected
Garlic with neck rot
Mode of spread and survival
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Survive as sclerotia
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Requires cool and moist weather
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Temp -15 to 20oc
Control
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Promoting rapid drying at harvest and good aeration in storage is
best for managing Botrytis on bulbs
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Additionally, cooler storage temperatures may help control the
disease