Garlic is attacked by many diseases and insects
pests. Therefore garlic growers need to know the details of symptoms
of diseases and insect pests attacking garlic and their control
measures for getting healthy crop. Diseases and insects pests, and
their control measures attacking garlic crop are described as under
blotch (Alternaria porri) appears
on leaves as small whitish sunken lesions with purple centres that
rapidly enlarge. The leaves fall over gradually. Spraying of Mancozeb
@ 2.5 g/litre of water at 15 days intervals gives good control.
blight (Stemphylium vesicarium) appears as small, yellow
to orange flecks or streaks on leaf. These soon develop into elongated,
spindle-shaped to ovate elongate, diffused spots, often reaching
the leaf tips. They usually turn gray at the centre, brown to dark
olive brown with the development of conidiophores and conidia of
the pathogen. The spots frequently coalesce into extended patches
blightening the leaves and gradually the entire foliage.
by Cercospora duddiae,this disease appears
on leaves as small, ash-coloured and irregular shaped spots scattered
on leaf lamina. The spots coalesce gradually and results in blightening
of foliage. Spraying of ziram or captan @ 2.0 g/litre of water or
copper oxychloride @ 3.0 g /litre of water at fortnightly intervals
gives good control.
mildew is caused by Leveillula taurica. Distinct pale-yellow
patches of variable size on abaxial surface of leaf associated with
powdery mass are its main characteristics. Sulphur fungicides @
2.0 g/ litre of water if sprayed at regular intervals of 15 days
after disease appearance gives good control.
plants infected with mosaic virus show typical symptoms of chlorotic
mottling and strips on first emerging leaf followed by pale-yellow
broken stripes, resulting in typical mosaic pattern on matured leaves.
Yellowish dots on leaves, whitish leaf margin or twisting of leaves
are also recorded on a few cultivars. Generally symptoms are mild
on younger leaves than on matured leaves. Bulbs harvested from mosaic
affected plants after maturity remain smaller in size and cloves
are fewer in number. Since virus is transmitted through aphids,
spraying of monocrotophos @ 0.5 ml/litre of water or methyl demeton
@ 0.75 ml/litre of water is useful.
(Thrips tabaci) are perhaps the most important insect pests attacking
garlic. They are most common during warm weather. They feed on leaf surfaces,
causing them to whiten or silver. They are slender about 1/25" long usually
hide in angles of leaves. Spraying of Malathion @ 1 ml/ litre or methyldemeton
@ 0.75 ml/ litre of water gives good control if sprayed at frequent intervals.
Four sprays of fluvalinate (0.04%) at fortnightly interval at Karnal and
malathion (0.1%) at Nasik gave best performance in controlling thrips.
Phorate @ 1 kg ai/ha at planting and 30 days after planting controls thrips
and bulb nematode
by Ditylenchus dipsaci, it is a tiny worm almost invisible to
the naked eye which invades the tissues of garlic, and can seriously reduce
the yield. The infestation causes the basal portion of mature plants to
swell and become spongy and frequently broken by longitudinal splits.
The tissue rots, the leaves and stems become rotten and twisted and the
plant is stunted. In severely infested plants, basal plants may be so
rotted that it pulls away when the plant is lifted, leaving the roots
in the ground. The nematodes are, however, not common in garlic in India.
soil fumigation with dichloro-propene-dichloropropane mixture @ 500 kg/ha
is recommended. Ethylene dibromide and dibromochloropropane (Nemagon)
should not be used as these leave residues in soil.
eriophyid mite, Aceria tulipae, a common pest of garlic is so
small that its infestations are frequently over-looked. Young garlic plants
injured by mites usually have destroyed and twisted leaves with conspicuous
yellow or light green streaking. The leaves may not emerge readily from
the cloves and leaf blades sepaerate poorly after emergence. Bulbs stored
for long period may be severely attacked by mites. The cloves wither and
bulbs lose their firmness.
callae and Glycohaqus domesticus
may attack on bulbs in storage. Fumigation of dry bulbs with methyl bromide
after harvesting and before storage control the mites. Application of
methyl bromide @ 1kg/1000 cubic feet for 2 hours at 26ºC
of bulbs in the field is noticed sometimes towards the start of maturity
stage of bulbs particularly when there are winter rains or excessive soil
moisture and nitrogen supply. This disorder is, however, not of permanent
nature and varies from variety-to-variety. Early-planting also causes
sprouting. Splitting is also noticed sometimes in some varieties, which
is due to delayed harvesting or irrigation after long spell of drought.
For past few years rubberification problem is noticed in Rajkot area and
also Nilgiri hills of Tamil Nadu. It is increasing day-by-day. The actual
cause for the disorder was since not identified, a trial was planned in
collaboration with TNAU at HRS, Ooty, during 1995-96. The effects of insecticides,
fungicides, micronutrients and growth regulator were studied. It was observed
that rubberification was totally controlled by application of micronutrients
i.e. zinc sulphate and ammonium molybdate. It was also controlled by neem
cake insecticides and growth regulator like GA.
Further studies are required
to eliminate this problem in different areas as the incidence is noticed
variably in different areas.
The aerial bulbil formation
is also quite common in garlic where lower temperature prevails for more
period or there are more temperature variation. It, however, does not
affect much on yield or quality of bulbs and varietal variation is noticed
where G-282 is seen more prone for this type of effect.
The rubberification and
premature sprouting of bulbs are main physiological disorders in garlic.
The reasons for these disorders are summarized as under for hill grown
garlic in Tamil Nadu.
- Rubberification and premature sprouting
of bulbs are noticed mostly in fields which are located in low-lying
areas of watershed where there is heavy deposition of nutrients alongwith
silt during heavy rains.
- These problems are severe in garlic
fields which are more frequently irrigated than the normal requirements
of garlic bulbs.
- With the application of higher levels
of nitrogen, there is an increased level of pre-mature sprouting of
bulbs which results in splitting and rubberification of bulbs.
- Rubberification incidence also increases
when higher level of nitrogen is applied in the form of urea.
- Due to increased levels of nitrogen,
in addition to the increased production of rubberized, there is an increased
level of thrips incidence in leaves during the later stage of crop.
The thrips lacerate leaves and cause severe damage to the crop. Through
lacerated wounds by thrips, there is a severe incidence of blast disease,
caused by Boltrytis allii, when crops is 70-90 days old, which
further deteriorates the quality of garlic bulbs.
- Short duration type of garlic (Mettupalayam
type) is more susceptible than long duration type (Singapore type).
- Premature sprouting of bulbs is more
in the crop (April-August) when there is high moisture level in soil
at maturity of crop due to heavy rains.
- Delayed harvest during rainy season
has increased premature sprouting and splitting of bulbs.
- Wider spacing of cloves at the time
of planting increases uptake of nitrogen and water by the individual
plants which increases premature sprouting and rubbenfication of garlic