AGRICULTURE AND IRRIGATION

DISEASES OF CROPS

Jowar.

Grain smut-kani roga or dune kani [Sphacetotheca Sorghi (L. K.) Clinton]-

The disease is more prevalent on kharif jowar than rabi jowar. Oa kharif jowar, it occurs from September to November and on rabi jowar from December to February. The disease is noticed at ear-head formation only. Individual grains are affected and in place of grains, black masses of spores are formed and in closed sori. Damage due to this disease is 6 to 10 per cent if the control measures are not adopted. Threshing of diseased and healthy earheads together is the main source of infection and spread of the disease. The disease can be controlled by treating the seed with sulphur dust of 200-300 mesh @ 110 gms. for 27.2 kg. of seed. The other diseases such as loose smut (kajali) and long smut (jamb kani) which are not very-serious can be controlled by the measures advocated for grain smut.

Downy mildew-kevada-(SclerospOra Sorghii (Kulk.) Weston and Uppal)-

The disease is prevalent in the months of August and September. On young leaves downy white growth mostly on lower surface, with yellowing on the corresponding upper surface is seen. Later the leaves become shredded. The main source of infection in the succeeding year is from the oospores shed in the soil from the affected crop. There is loss of vigour in plants resulting in reduced yields. Damage is between 3 and 10 per cent. The control measures consist of -syste matic rouging and burning of affected plants, rotation and growing of resistant varieties.

Bajri.

Ergot disease-Chikta [Claviceps. microcephala (Wall.) Tal.]

The disease occurs in the middle of August and September. The grains in the earhead are transformed into black bodies called sclerotia. which contain a poison called ergotin. which is fatal to cattle and human beings. The losses range between 3 and 10 per cent. Soursces of infection of this disease are sclerotia mixed with bajri seeds by sugary secretion carried by insects and rain drops splashed by wind. The sclerotia can be separated from the healthy seed by steeping the seed in 20 per cent salt solution. The sclerotia and pieces of broken sclerotia and light seeds float and these may be removed and burnt. The steeped seeds are to be washed and dried before consumption. Deep ploughing may also be practised.

Downy mildew-Gosavi [Sclerospora Graminicola (Sacc) Schroet]-

The disease occurs in the months of August and September. On voung leaves, downy white growth mostly on lower surface, with vellowing on corresponding upper surface is seen. The shredding of leaves is uncommon. On the earheads instead of grains small greenish scale like growth is observed giving the appearance of green ear which is very commonly seen in the field. The main source of infection is oospores which are shed in the soil from the previously affected crop. The extent of damage is between 3 and 10 per cent. The control measures consist of systematic rouging and burning of aflected plants, rotation and growing of resistant varieties.

Wheat.

Black stem rust-Tambhera (Pnccinia Graminis Tritici, Eric and Henn.)-

Tambhera occurs from November to February. The disease manifests in the form of reddish brown elongated spots on the leaves and stem in early as well as the later parts of the season. At the maturity of the crop these spots turn black. The disease is spread by spores carried by wind and rain. There is loss of vigour in the plants resulting in reduced yields. Damage caused by tambhera is as high as 60 to 70 per cent under severe disease conditions. The disease is controlled by growing resistant varieties viz., for irrigated-NI-917. NI-315, Hy-65 NI-146, NI-284-S, K-25, NI-28, NI-62 and for dry-N-59. N-125.

Loose smut of wheat-kajali [Ustilago Tritici (Pers) Rostr].-

The disease occurs from February onwards and is visible on earheads. Only the earheads arc affected. The inflorescence, the rachis and awns are transformed into black mass. The disease is carried internally in the seed. Damages range between 3 and 10 per cent. The disease can be controlled by washing the seed with water and spreading it on a threshing yard or galvanised iron-sheets and drying for 5-6 hours, during the hottest part of the day. in the months of April or May.

Paddy.

Paddy blast-Tikkya-(Piricularia Oryzae) Cav-

The disease is found on seedlings from July to August and on grown up crop from September to November. There is loss of vigour in the crop and due to neck infection there may be complete sterility resulting in reduced yields. Under severe disease conditions the losses may range from 45 to 75 per cent. The sources of infection are wind borne, from the debris of the previous crop and seeds from infected areas. The disease is controlled by treating seeds with organo-mercury at the rate of 4 Ozs. per 45.359 kg. (100 lbs), of seeds. Before transplating. the seedings should be dipped in Bordeaux mixture 3: 3: 50 or any copper fungicide should be given. Tolerant varieties viz., early ambemohor-39, Kolhapur scented, patni-6. bhadas-78, krishnasal-10, antrasal-90; 67 and 200 could be grown, pending evolution of resistant varieties.

Helminthosporium leaf spot-Tikkya.

(Helminthosporium Oryzae) Breda-de-Haan-

The infected seeds show dark brown spots with white centre and yellow halo on the leaves and glumes. Losses may vary from 6 to 10 per cent. The measures advocated for paddy blast may be followed to control the disease.

Tur.

Tur wilt-Mar-(Fusarium Oxysporium F. Udum)-

The disease attacks seedlings as well as mature plants killing the hosts outright. Damage is estimated to be up to.50 per cent. Crowing of resistant varieties is the only way of controlling this disease.

Groundnut.

Leaf spot of groundnut-Tikka [Cercospora Personata] (B & C.) Ell & Everh Cercospora Arachidicohi Hori-

The disease occurs from July to September on late varieties when the crop is 1 months old. Roundish purplish brown or irregular spots appear on the leaves. There is loss of vigour in the crop resulting in low yields. The source of infection is mostly plant debris. Tikka is controlled by spraying the crop in the third week of July with 3: 3: 50 bordeaux mixture or any copper compound. It necessary, second spraying in the third week of August may be given and third spraying it required, in the third week of September. Besides. it can be successfully controlled bv sulphur dusting (200 to 300 mesh) at the rate of 6.804 kg. (15 lbs.) per acre.

Sclerotium wilt-mar-[Sclerotium Rolfsii (Sacc)]-

The disease occurs from July to September and is recognised by wilting of plants. Partial wilt is also common. Due to this disease, root, stem and collar are usually affected. When the disease is fully developed it forms small pale brown mustard seedlike bodies known as selerotia. The loss due to the disease is between 1 and 5 per cent. The source of infection is plant debris and selerotia. The controlling measures include rotation with maize or millet crops, deep ploughing or burning of infected plant debris.

Cotton.

Wilt-Mar-[Fusarium Vas Infectum (A & K) Sh. & Haan.]-

The disease occurs on seedlings in October and November. The losses caused by the disease may range from 60 to 75 per cent under severe conditions. The pathogen is found in the soil from where the infection takes place. Mar can be controlled by growing resistant varieties like Virnar (197-3), G-22 (1422), G-46 (1946) and Y-1.

E. Anthracnose of cotton-[Kavali-Colletotrichum Indicum Dastur]-

The disease occurs in seedling and boll forming stages. Losses caused vary from 15 to 50 per cent under severe disease conditions. The spread of the disease is from infected seeds and affected plant debris. The disease can be effectively controlled by treating the seeds with mercurial fungicides at the rate of 2 Oz. for 6.804 kg. (15 lbs.) of seeds, burning of affected plant debris, 3 to 4 sprayings with 3: 3: 50 bordeaux mixture or any other copper fungicides during the life period of the crop.

Bacterial blight-angular leaf spot-black arm of cotton-karpa [Kanthomonas Malvacearum (smith) Dow.]

The disease spreads from July to September on dry cotton and from July to March on irrigated cotton. Due to blighting there is loss of vigour in the crop resulting in reduced yields. The losses range from 15 to 25 per cent. The organism lives in seeds and if such seeds are sown they produce diseased plants. Karpa can be controlled by treating seeds with mercurial fungicides at the rate of 3 gms. to 1 kg. of seeds and burning of affected plant debris.

Grey mildew or Areolate mildew-Dahiya-(Rammularia areola) Atk-

The disease occurs from September to November. Yellowish angular discoloration is visible on the upper surface of the leaves while on the corresponding lower surface ash or gray coloured growth of the fungus is seen. Severe infection causes defoliation resulting in reduced yields. The losses vary from 15 to 50 per cent. The organism is- disseminated 'through plant debris and through,air which infects the crop. The disease can be effectively controlled by dusting sulphur (200-300 mesh) at the rate of 7 to 10 kgs. per acre from the middle of August. The dusting should be completed by first week of September. If necessary, another dusting may be given during the life of the crop.

Sugarcane.

E. Smut-Kajali (Ustilago Scitaminla) (Rabh.) Syd.-

The disease occurs from January to March affecting the canes which produce long whip like shoots covered with black masses of spores. Smutted shoots may also arise from lateral buds. The losses range from 5 to 10 per cent. Bagging the affected shoots helps in checking the further spread of the disease. Irrigating the field 2-3 times before planting, use of smut resistant strains of sugarcane and rouging out and burning the entire diseased clumps and smutted shoot or shoots in the clump can control the disease.

Grassy shoot-gavtad vadicha rog-virus disease.-This is a virus disease of sugarcane and is of common occurrence on variety Co-419.

Crop affected by this disease results in poor stunted growth and number of shoots develop from the eye buds. For control, the sugarcane sets should be treated by dipping in hot water at 53C for 40 minutes.

Chillis.

Fruit rot-kavadi-(Colletotrichum capscici) (Syd. Butler & Bisby)-

The disease occurs in the months of November and December on dry as well as irrigated chilli crop. There is rotting of fruit which later on drop, resulting in reduced yield. The loss varies from 15 to 20 per cent under severe disease conditions. The source of infection is from seeds and plant debris. Seed treatment with organomercurial fungicides and spraying 3 times with bordeaux mixture 3:3: 50 or any other copper fungicide from (lowering stage onwards helps in reducing the disease.

 

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