Symptoms

This is a seed-borne fungal disease. The leaves show round to oval or irregular brown spots which may coalesce to cause withering of tissues. A velvety growth may be seen on the glumes. Sometimes browning or greyish browning may be seen at the neck region. The grains show reddish brown discolouration. These spots appear like sesame seeds: hence this condition is also known as sesame leaf spot.

Symptoms

This is a fungal disease that spreads through weeds and pathogens. The first symptom seen on the leaf sheath is the appearance of greenish grey lesions. Later, lesions turn to straw colour and increase in size which girdles the stem. The leaf blade of the affected sheath dries up from the tip downwards. The grains are shrivelled and poorly filled.

Symptoms

This is a seed-borne bacterial disease. It is characterized by the appearance of yellow colour, water-soaked lesions on both the edges of the leaves. Later, they coalesce and the entire surface turns straw coloured. The affected leaves roll completely, droop and ultimately the tillers wither away. These symptoms usually appear 4–6 weeks after transplanting. Affected plants produce chaffy grains. Use of high nitrogenous fertilizer rates favours blight epidemics especially where susceptible cultivars are grown.

Symptoms

This disease is spread through viral particles. Older leaves turn yellowish orange starting from the tips and spreading downwards to eventually cover the entire leaf. Young leaves are mottled with pale green to whitish spots. Root development is poor and grains are usually covered with dark brown blotches. Plants become stunted and bear poor panicles with empty glumes. This disease is transmitted by the green leaf hopper (Nephotettix virescens).

General management of diseases

• Take cow's urine in a mud pot and allow it to ferment for one week.
• Spraying this over the crops controls bacterial and fungal diseases.
  
• Mix one litre of cow's urine with one litre of buttermilk and eight litres of water.
• Spraying this extract over the crop also controls bacterial and fungal disease.
  
• Mix 300 ml of sweet flag extract with one litre of cow's urine and 8.7 litres of water.
• Spraying this extract controls the spread of disease.

Nutritional disorders

The growth of a crop will be abnormal when any of the essential nutrients is deficient in the soil. Nutrient deficiency in rice can be identified by certain characteristic deficiency symptoms. A few major nutrients – along with their deficiency symptoms – are listed below:

Poor tillering and chlorosis of leaves are observed with deficiency. The intensity of the green colour depends on the intensity of nitrogen deficiency. With excess nitrogen, the plants produce bluish green leaves and become highly susceptible to pest and disease attack.

Phosphorous deficiency is often found in calcareous, heavy black and alkaline soils. Lower or older leaves lose their normal green colour and poor tillering is observed. Bluish green leaves are observed even when the level of nitrogen is normal.

Intensive multiple cropping with less potassium application leads to depletion of potassium. The deficiency symptoms appear on older leaves. These leaves lose their normal green colour and develop brown or yellow patches from the leaf tip extending towards the leaf base. The midrib portion is green in colour and resembles a leaf affected by bacterial leaf blight. Potassium deficiency leads to intense pest and disease attacks and the crop lodges due to a weak stem.

Zinc deficiency is more easily found in heavy clay, calcareous, highly alkaline soils and soils with improper drainage. Chlorosis of lower leaves and bleaching of the midrib portion is seen with the top one- third leaves remaining normal. The symptoms are noticed in young leaves and disappear at about 25 days after transplantation. Severe deficiency leads to the production of reddish brown necrotic spots which merge and extend throughout the leaf. The leaves will be
small, spindle shaped, brittle and break easily.

Iron chlorosis of young leaves is common in rain fed rice and in alkaline and calcareous soils. It is also common when the crop is irrigated with water having high carbonates and when heavy doses of phosphatic fertilizers are applied. Inter-veinal chlorosis of leaves is observed and, in cases of severe deficiency, the whole leaf appears bleached. Drying starts from the tip and extends to the inner parts.
The yellow leaves turn brick red, then dry and drop.