MULBERRY CULTIVATION (CONT...12) - DISEASES AND INSECT PESTS

Diseases:  There are different kinds of diseases of mulberry which are caused by fungi, bacteria, viruses and also mineral deficiencies or physiological disorders. Of these ten or twelve diseases cause much damage to mulberry plants.

White root rot: White root rot is caused by the pathogen Rosellinia necatrix, Berlesse, belongingto the class Ascomycetes. The diseased mulberry plants become weak, the leaf buds grow feebly, the leaves wither off and soon the plant dies.

Violet root rot: This is caused by the fungus Helicobasidium mompa, Tanaka, belonging to the class Basidiomycetes. The chief symptoms of the disease are, sudden withering of leaves and collapse of plants during rainy season.

Controls of root rot diseases: As soon as the symptoms appear, the diseased plants should be uprooted. A meter deep pit is dug around the diseased plants and the soil excavated should be piled up in an isolated place to prevent the spread of the diseases.

Mulberry trunk rot: This disease is caused by Polyporus hispidus (Bull) Fr. belongs to the class Basidiomycetes. The affected trees show symptoms such as drying up of branches and rotting of branches and trunk, terminating in the death of the tree.

Leaf spot diseases: Several leaf spot diseases are reported on mulberry. They are caused by Cercospora moricola Cooke, Septogloeum mori Briosi and Cav.

Prevention and control: Spraying suitable fungicides (e.g. Difolatan 0.2 percent) on the Toungleaves (soon after picking or pruning, i.e. before the onset of the incidence) pre­ vents the infection. The sprayed leaves should be fed to silkworms only after a certain period of time to avoid toxicity.

Powdery Mildew: This is caused by the pathogen Phyllactinia corylea (Pets) Karst, belonging to the class Ascomycetes. The disease is common in all temperate regions.

Prevention and control: Dusting fine Sulphur or spraying dithane, Sulphur suspension or lime Sulphur mixture on the back of the leaves may be effective.

Mulberry Rust: It is caused by the pathogen Aecidium mori (Barcl) Syd. et. Butler, belonging to the class Basidiomycetes. The pathogen infects the leaves and green woody portions of the plant.

Prevention and control: Spraying Sulphur suspension or lime sulphur mixture in appropriate concentration on the plants is effective in controlling the disease

Dogare blight: Dogare blight is caused by Diaporthe nomurai, Hara.

Prevention: Selection of resistant mulberry, high cut pruning, and cutting and burning of the infected plants are recommended to prevent the disease.

Twig blight: This is also called "Megare" disease and is caused by the pathogen Gibberelle‑mo‑ricola (De Not) Sacc.

Prevention and control: Removal of infected twigs and spraying the plants with suitable fungicides recommended for checking the Dog are blight disease are effective in preventing megare blight also.

Shownia disease: The leaves develop rusty brown patches, showing deficiency of potash, proteins and sugar contents. The exact cause of the disease is not established. This disease is common in some parts of West Bengal in India. The diseased leaves are poisonous to the silkworms and may cause flacherie. Heavy rains may favor the onset of this disease. Potash manuring may prevent the incidence.

Bacterial diseases: Three different pathogenic bacteria cause diseases in mulberry:

Bacterium moricolum, Yendo et. Higuchi: This short rod shaped, non motile, gram positive bacterium erodes the base of the twigs and forms a whitish colony around.

Diseases caused by viruses: Mulberry plants are affected by some viruses and mycoplasma of which two are common.

Dwarf disease: This disease is caused by mycoplasma. The disease is transmitted by insect vectors such as leaf hoppers, Hishimon‑yokobai (Hishimonus sellatus uhler) and Hishimon‑modoki (Hishimonoides). Due to this disease, the leaves become yellow, and disorderly arranged.

Mosaic disease: This disease causes wrinkling of the ventral surface of the leaves together with chlorotic conditions. The leaves become distorted and twined.

Prevention and control: The following steps are recommended for controlling the virus diseases:

(1) Growing resistant varieties.

(2) Selection of saplings and cuttings from disease free plants and growing them in disease free plots.

(3) Proper cultural practices.

(4) Eradication of insect vectors by spraying suitable insecticides.

Deficiency diseases of mulberry: Apart form diseases caused by various pathogenic agents, mulberry plants show symptoms of many deficiencies in minerals. The following are some of the common deficiency diseases noticed in mulberry.

Nitrogen deficiency: This causes a slow, weak growth of plant with less branching and chlorosis of leaves. The young green leaves show mottling and chloritic spots.

Potassium deficiency: The deficient plants show marginal scorching (drying) of leaves and later the leaves become course, non‑juicy and necrotic.

Phosphorus deficiency: This becomes apparent in the plants as intra‑veinal chlorosis of older leaves. The chlorosis spreads throughout the leaf and this is followed by marginal necrosis and defoliation.

Magnesium deficiency: Magnesium deficiency causes chlorosis of older leaves and necrotic spots on the leaves. The leaf tips and margin become dried and scorched.

Calcium deficiency: Calcium deficiency causes deformation of young leaves, with necrosis along the veins and makes the leaves pale.

Sulphur deficiency: There will be slight chlorosis of the leaves with general lack of new growth. The stem becomes slender.

Insect Pests: Mulberry, like most of the economic plantations and field crops is often attacked by various insect pests.

Lepidopteran pests

Diacrisia obliqua WALKER: Belongs to the family Arctidae of Lepidoptera commonly known as "Bihar hairy caterpillar". It is a polypbagous pest and is responsible for the highest damage to mulberry plants.

Life cycle and habit

Egg: 1000 ‑ 1200 eggs green in color with a metallic shining color are laid by the female moth in small batches on the lower surface of the leaves. The incubation period is five to seven days.

Larva: The hatched larvae are dull white in color with prominent black head and the body covered with sinall hairs. They measure 0.2 cm in length.

Pupa: They pupate in loose soils. The pupa lies inside a thin silken cocoon formed by the interwoven shed hairs of the larva. It measures about 2 cm and is dark brown in color. The pupation lasts for 12‑14 days.

Imago: The moths are light brown in color. The abdomen is brick red with rows of black dots on lateral and mid dorsal sides. The wings have scattered black spots. The female moth with wing expanse of 4.5 cm measures 1.75 cm in length. They are nocturnal in habit.

Control measures: (i) Collection of egg masses in a mechanical way to reduce the number of successive generations. Early stage larvae can be identified by their gregarious habits and the dried leaf on which they feed can be collected and destroyed. (ii) Deep ploughing and flood irrigation is useful in killing the pupae which pupate in soil. (iii) Biological control: In nature, a Hymenopteran parasite, Apanteles obliqua, is found to parasite the larvae by laying the eggs on the body. The parasites puncture the host larva to come out for pupation, thus killing the host. (iv) Chemical control: 0.2 percent D.D.V.P. can be spread to kill the larvae and the sprayed leaves can be used for silkworm rearing after three days.