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Hydroponics

Diseases and Their Management:

Fusarium Wilt:

This is most common disease of tomato. The first symptom of the disease are clearing of the veinlets and chlorosis of the leaves, which soon turn brown, dry, droop and finally wilt. If the stem and roots are sliced, dark brown or black discoloration of the vascular tissues can be observed. The infected plants may wilt and die within few days.

Control:

  • Prevention of disease organisms from entering the growing system.
  • Proper disinfection of trays, rafts, beds and other materials.
  • Use effective disinfectants like 10% solutions of chlorine bleach or hydrogen peroxide based products intended for hydroponic systems.
  • Encourage healthy plant growth because stressed plants are more vulnerable to root pathogens.
  • Maintain proper aeration in root zone.
  • Use a balanced nutrient solution regularly check total soluble salts and pH levels.
  • Fumigant the growing system before planting.
  • Use resistant varieties.

Late blight of tomato:

The fungus attacks all above ground parts. Affected plants look like been damaged by frost. Irregular greenish black or brown leaf spots develop. Lesions enlarge under moist, cool conditions destroying the whole plant. Fruit symptoms include grey brown lesions which cover the whole fruit. Later on these lesions become copper brown with a rough surface.

Control:

  • Use disease free planting material.
  • Late blight can be controlled by spraying plants with Bordeaux mixture or Dithane (0.2 percent).

Damping-off and root rot:

There are two types of damping-off namely Pre-emergence damping-off and Post-emergence damping off. Pre-emergence damping-off consists of killing of the seedlings during initial stages of seed germination. Post-emergence damping-off consists of fast shrinking and darkening of the cortical tissues of the hypocotyl. Under hydroponic conditions, late damping-off merges into lower-stem and root rot. The roots become discolored. Severely infected plants wilt due to the rotting of collar. Shoots can be separated easily from roots when they are pulled up by little force.

Control:

Before planting treat the seed with hot water at 52°C for 30 minutes, and after drying thoroughly, followed by Ceresan dusting at 0.5 percent of the weight of seed. Mixing of Arasan with nutrients solution after the seedlings have emerged is useful.

Fusarium stem and fruit rot:

The most common symptom of this disease is the appearance of soft, dark brown lesions on the stems at nodes or injury sites. Black water-soaked lesions initially develop around the calyx and eventually spread down the sides of the fruit. Fungal mycelia become more visible on the lesions under high humidity conditions.

Control

  • Maintain a clean system and good sanitary conditions to prevent the development of this disease.
  • Diseased plants must be removed from the system and carefully buried away.
  • Maintain good aeration in nutrient media and maintain relative humidity below 85%.

Early blight:

The disease first appears as circular to angular, dark brown to black spots on the leaflets. When spots are several, then leaves wither up and drop off. On the stem dark spots occur. Collar rot is a form of stem lesion which begins in the seedling stage. Fruits are infected in the green or ripe stage, usually at the stem end but also through growth cracks and other wounds.

Control:

Fungicidal sprays, preferably with copper fungicides at 15 days interval effectively control the disease.

Grey mould:

Tender plant parts such as young leaves, stems and flowers are affected. Affected plants have light brown or grey lesions on stalks which turn black. Fruits show irregular grey or pale green spots with pale margins. Grey mold usually develops on the margins followed by soft rotting. In the damping-off phase, seedlings may collapse and drop over.

Control:

  • Growth medium treatment and ample ventilation are essential.
  • Maintain relative humidity below 85% and avoid the formation of free water on the plant and fruits.
  • Control can also be achieved by applying benomyl.

Anthracnose

It the most common fruit-attacking disease of capsicum and tomato and hence it is also known as ripe-fruit rot. The symptoms first become visible on fruit as circular and sunken spots with black margins in the skin. The sunken-spot is covered with a pinkish mass of fungal spores. As the disease progresses the spots expand, forming dark spore producing bodies of the fungus. This disease is usually less frequent and less severe under hydroponic system.

Control:

  • The fungus is seed-borne and can be controlled by seed treatment.
  • The secondary spread can be controlled by spraying copper based fungicides (0.3% ifolatan, 0.2% Dithane M-45) at fortnightly interval.

Powdery mildew:

This is common disease on cucumber, capsicum, tomato and lettuce. It first appear as light green to bright yellow spots on the upper surface of the leaf. It is usually more noticeable when white, powdery growth appears on the upper as well as on the lower surface. It results in deformity of the leaves. In severe infections, the infected leaves wither off. In case of capsicum, leaves may die and fall off. The fruit yield is very much reduced and the fruits are small in size.

Control:

  • Maintain relative humidity levels below 85% and promote proper air circulation.
  • Prune and remove disease plant tissues.
  • All plant debris should be removed and system must be thoroughly cleaned.

Leaf spot:

The symptoms initially found at the lower leaves and then spread out to the upper leaves. Lesions typically are brown and circular with small light grey centers and dark brown margins. Under severe infections, defoliation occurs. In lettuce, infected plants would lose their market value due to low quality products obtained.

Control:

Fungicides (Bordeaux mixture 1%, Dithane M-45 0.2%, Benlate or Bavistin 0.1%) are needed to manage the disease during disease development period.

Bacterial spot:

Leaves, fruit and stems are affected. Leaf lesions begin as small, yellow-green lesions on young leaves. Then grow as water-soaked spots and become necrotic with brown centers and thin chlorotic borders on older leaves. Lesions often are more numerous at the tip and margin of the leaf where moisture is usually retained. Under dry conditions lesions centers become necrotic. In severe infections, defoliation is common. Fruit symptoms generally occur as raised, brown and roughened lesions

Control:

  • Use certified pathogen-free seed and disease-free transplants.
  • Pepper plants should be routinely sprayed with based bactericides to maintain protective cover on the foliage and fruit.
  • Use of “Agri Phage” in hydroponic and glasshouse transplant production is very helpful to reduce disease development.

Management in Hydroponic System:

For successful farming, following points must be considered;

  • Doors of the hydroponic system must be always properly closed.
  • Foot-path disinfection with suitable disinfectant such as iodine or bleach.
  • Sanitary measures should be adopted properly because a neat system provides conducive environment for healthy plant growth.
  • Sterilization of equipment, tools and surfaces should be properly followed. Equipment should be soaked for 30 minutes in 10% bleach solution and then rinsed with water.
  • Use of pathogen-free planting materials must be ensured.
  • Use of pathogen-free water is necessary, especially if it is surface water. Water must be treated. Water from deep bores should be used.
  • Maintain adequate levels of dissolved oxygen (11-14%).
  • Good hygiene and control of insect vectors is essential.
  • Sterilization of recirculating nutrient solutions is essential. For this purpose, exposure of nutrient solutions to UV radiation and filtration of the solutions are best choices.
  • Monitor the plants regularly to prevent any accidental introduction of pests.
  • Maintain a weed free hydroponic system at all times.
  • Heavily-infested plants should be immediately eliminated and must not be left in the hydroponic overnight.
  • Biological control of plant pathogens must be done. Microbiological antagonists of root pathogens and the use of microorganisms for cross protection against specific diseases are available. There are a number of commercially available products containing Trichoderma.
  • Use commercially available root growth promoters for weak roots.
  • Fungicide incorporation in nutrient solutions. Treatments of recirculating systems with chemical fungicides is sometimes recommended.

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