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GINGER
Plant protection
Diseases : Soft rot or rhizome rot, Bacterial wilt, Leaf spot
Pests : Nematode, Shoot borer, Rhizome scale, Minor pests
Soft rot-above ground symptoms
Rhizome rot symptoms
The disease is soil-borne and is caused by Pythium aphanidermatum. P. vexans and P. myriotylum are also reported to be associated with the disease. The fungus multiplies with build up of soil moisture with the onset of southwest monsoon. Younger sprouts are the most susceptible to the pathogen. The infection starts at the collar region of the pseudo stem and progresses upwards as well as downwards. The collar region of the affected pseudo stem becomes water soaked and the rotting spreads to the rhizome resulting in soft rot. At a later stage root infection is also noticed. Foliar symptoms appear as light yellowing of the tips of lower leaves, which gradually spreads to the leaf blades. In early stages of the disease, the middle portions of the leaves remain green while the margins become yellow. The yellowing spreads to all leaves of the plant from the lower region upwards and is followed by drooping, withering and drying of pseudo stems.
Management
Treatment of seed rhizomes with mancozeb 0.3% for 30 minutes before storage and once again before planting reduces the incidence of the disease. Cultural practices such as selection of well drained soils for planting is important for managing the disease, since stagnation of water predisposes the plant to infection. Seed rhizomes are to be selected from disease free gardens, since the disease is also seed borne. Application of Trichoderma harzianum along with neem cake @ 1 kg/ bed helps in preventing the disease. Once the disease is located in the field, removal of affected clumps and drenching the affected and surrounding beds with mancozeb 0.3% checks the spread of the disease.
Bacterial wilt-yellowing and wilting symptoms
Bacterial wilt caused by Ralstonia solanacearum Biovar-3 is also a soil and seed borne disease that occurs during southwest monsoon. Water soaked spots appear at the collar region of the pseudo stem and progresses upwards and downwards. The first conspicuous symptom is mild drooping and curling of leaf margins of the lower leaves which spread upwards. Yellowing starts from the lowermost leaves and gradually progresses to the upper leaves. In the advanced stage, the plants exhibit severe yellowing and wilting symptoms. The vascular tissues of the affected pseudo stems show dark streaks. The affected pseudo stem and rhizome when pressed gently extrudes a milky ooze from the vascular strands. Ultimately rhizomes rot.
Management
The cultural practices adopted for managing soft rot are also to be adopted for bacterial wilt. Seed rhizomes must be taken from disease free fields for planting. The seed rhizomes may be treated with streptocycline 200 ppm for 30 minutes and shade dried before planting. Once the disease is noticed in the field, all beds should be drenched with Bordeaux mixture 1 % or copper oxychloride 0.2%.
Phyllosticta leaf spot
Leaf spot is caused by Phyllosticta zingiberi and the disease is noticed on the leaves from July to October. The disease starts as a water soaked spot and later turns as a white spot surrounded by dark brown margins and yellow halo. The lesions enlarge and adjacent lesions coalesce to form necrotic areas. The disease spreads through rain splashes during intermittent showers. The incidence of the disease is severe in ginger grown under exposed conditions.
Management
The disease can be controlled by spraying Bordeaux mixture 1 % or mancozeb 0.2%.
Root knot (Meloidogyne spp.), burrowing (Radopholus similis) and lesion (Pratylenchus spp.) nematodes are important nematode pests of ginger. Stunting, chlorosis, poor tillering and necrosis of leaves are the common aerial symptoms. Characteristic root galls and lesions that lead to rotting are generally seen in roots. The infested rhizomes have brown, water soaked areas in the outer tissues. Nematode infestation aggravates rhizome rot disease.
Dry rot in ginger due to Pratylenchus sp
Management
The nematodes can be controlled by treating infested rhizomes with hot water (50°C) for 10 minutes, using nematode free seed rhizomes and solarizing ginger beds for 40 days. In areas were root knot nematode population is high, the resistant variety IISR-Mahima may be cultivated.
Insect pests
Symptom showing bore-hole with frass extrusion
The shoot borer (Conogethes punctiferalis) is the most serious pest of ginger. The larvae bore into pseudo stems and feed on internal tissues resulting in yellowing and drying of leaves of infested pseudo stems. The presence of a borehole on the pseudo stem through which frass is extruded and the withered and yellow central shoot is a characteristic symptom of pest infestation. The adult is a medium sized moth with a wingspan of about 20 mm; the wings are orange-yellow with minute black spots. Fully-grown larvae are light brown with sparse hairs. The pest population is higher in the field during September-October.
Management
The shoot borer can be managed by spraying malathion 0.1 % or monocrotophos 0.075% at 21 day intervals during July to October. The spraying is to be initiated when the first symptom of pest attack is seen on the top most leaves on the pseudostem. An integrated strategy involving pruning and destroying freshly infested pseudostems during July-August (at fortnightly intervals) and spraying malathion 0.1% during September-October (at monthly intervals) is also effective against the pest.
Rhizome infected by scale
The pest can be managed by treating the seed material with quinalphos 0.075% (for 20-30 minutes) before storage and also before sowing in case the infestation persists. Severely infested rhizomes are to be discarded before storage.
Larvae of leaf roller (Udaspes folus) cut and fold leaves and feed from within. The adults are medium sized butterflies with brownish black wings with white spots; the larvae are dark green. A spray with carbaryl (0.1 %) or dimethoate (0.05%) may be undertaken when the infestation is severe.
Root grubs occasionally feed on tender rhizomes, roots and base of pseudo stems causing yellowing and wilting of shoots. The pest can be controlled by drenching the soil with chlorpyrifos 0.075%.
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