Author: SHAILENDRA KUMAR
Tomato is one of main crops used to cultivate under greenhouses. The several pathogenic diseases like fungal, bacterial, viral make losses in yield and reduce quality of produces. Correct diagnosis and timely taken steps for management of disease is must to manage diseases under green houses. In management strategies alone with chemicals sanitation or removal of primary source of inoculums is an important aspect.
The most intensive form of horticultural production is the cultivation of crops under green house conditions. It provides high quality, yield and value to the crops. But the major challenge in the green house is to manage insect and pest as it has also congenial atmospheric condition for their establishment and growth. High humidity, temperature, high planting density and air-exchange restrictions are few parameters that create favorable microclimate for fungal, bacterial and insect transmitted viral diseases. The losses due to these diseases under green houses condition can be up to 100%. Therefore proper diagnosis and suitable management strategies are very necessary to control the diseases, which are as follows:
- Early Blight (Alternaria solani, A. alternata f.sp. lycopersici):
Symptoms:
- On leaves, symptoms first appear on older foliage with small dark spots enlarge into circular lesions consisting of concentric rings. The tissue surrounding the lesions becomes yellow and the spots later become irregular in shape.
- Stems and petioles affected by early blight have elliptical concentric lesions, which drastically weaken the plant.
- Mostly disease appears in vegetative phase of plant growth before flowering.
Cultural method:
- Use of resistance varieties
- Field Sanitation should be followed as plant debris provides source of inoculums for disease.
- Minimize the humidity at plant canopy.
- Spray of Bordeaux mixture 1%.
- Two spray of Chlorothalonil 75 WP @0.2% or Cymoxanil 8% + Mancozeb 64% WP @ 0.2% at 8 days interval is effective against the disease but spray must be started soon after infection on floral part.
- Late Blight (Phytophthora infestans):
Symptoms:
- Blight appears on foliage as light-pale green water soaked area. The lesions are wet in morning and dried, shriveled in daylight.
- In moist and cloudy weather, a downy white fungus develops near the outer margin of lesion on underside of the leaves.
- Green and ripe fruit affected by the blight appear as greenish brown and internal tissues become spongy with bad odour.
Cultural method:
- Use and planting of healthy seeds at disease free area.
- Field Sanitation.
- Staking of plants should be done. Fruit touches the ground is more prone to the disease.
- Preventive sprays of Mancozeb 75% WP @ 0.25% (2.5 gm per liter water) provide good control in cloudy, cold and drizzling weather but spray interval should be 5 to 7 days. One spray of Metalaxyl 4%+ Mancozeb 64% @0.2% (2gm per liter water) is very effective when applied within two days of infection.
- Disease appear in severe forms during the month of September to November.
- Leaves show downward rolling, curling, twisting and chlorosis.
- Plants show stunting, shortening of internodes, bushy appearance, no flowering and fruiting at later stage of virus infection.
- Sometimes leaves show light and dark mottle symptoms.
Cultural method:
- Use of resistant variety.
- Roughing of infected plant
- Raise healthy seeding under insect proof net structure.
- Removal of weeds.
- Border and intercropping with marigold (one row of marigold after 15 row of tomato)
- Use of yellow sticky cards.
- Spray neem seed kernel extract (NSKE) 5% Or azadirachtin 5% W/W neem extract concentrate @ 80 g in 160 l of water/acre.
- Roots of seedling should be dipped in Imidaclorprid 17.8 SL@ 0.03% for 1-2 hours before transplanting.
- Spray Dimethoate 30% EC @ 396 ml in 200-400 l of water/acre
- Spray Imidacloprid 17.8 SL @ 60-70 ml in 200 l of water/acre or Thiamethoxam 25 WG @ 80 g in 200 l of water/acre.
- Damping off: Pythium spp., Pythapthora spp.
Diagnosis:
- The seed may rot or the seedlings may be killed before they emerge from the soil.
- The stem of young seedlings may also be attacked after emergence showing water soaking and shriveling of stem which fall over and die.
- In a nursery, the disease may start in patches and in the course of 2 -4 days the entire lot may be destroyed.
Cultural methods:
- Excessive watering and poorly drained areas of field should be avoided
- Use raised beds: 15 cm height is better for water drainage or use pro-trays for raising seedlings.
- Seed treatment with Trichoderma viride 1 % WP @ 9 g/Kg of seed.
- Seed treatment with captan 75% WP @ 20-30 g/Kg seed
- Soil drench with Metalxyl 8%+ Mancozeb 64% WP @ 2 g/litre of water/acre as soil drench in nursery.
- Botrytis Mold: Botrytis cinerea
Diagnosis:
- Superficial spots have a pale halo with a brown to black pinpoint spot in the centre.
- On unripe fruit, the halo is pale green or silvery, and generally the tissue inside the halo is paler green.
- On ripe fruit, the halo is pale yellow.
- The lesions on fruit appear as light brown to gray spots, irregular in shape. A dark gray, velvety growth develops on the fruit surface later, followed by a watery, soft rot.
- Affected leaves show light tan or gray spots, and the infected areas become covered by a brown fungal growth. The leaves wither and collapse. The disease is favored by cool, wet and humid condition. Temperatures of 17–23 °C are ideal for disease development.
- Iprodione + Carbendazim (quintal) 1g/litre at 5-7 days interval should be used as protective and curative application.
- In the greenhouse, maintain a relative humidity of less than 80%, especially during the night. Remove all clippings from the plant bed if seedlings are pruned.
References:
Dimitrios I., Tsitsigiannis., Polymnia P., Antoniou., Sotirios E., Tjamos., Epaminondas J., Paplomatas. Major diseases of Tomato, Pepper and Eggplant. The European Journal of Plant Science and Biotechnology. Global Science Book .2008.
About Author / Additional Info:
I am Plant Pathologist. Currently Providing my services in Agricultural Private Sector.