AGRICULTURE AND IRRIGATION
DISEASES OF CROPS
Of cereals: Jowar: Grain smut, kani or dane kani (Sphaceteotheca sorghi, link, clinton): The disease is noticed after the ear-heads have formed. The grains are converted to black masses of spores. The disease generally occurs from September to November on kharif jowar and from December to February on rabi jowar. The kharif jowar is more susceptible to this disease than the rabi jowar. The disease can be controlled by treating the seed with sulphur dust of 200-300 mesh at the rate of 100 grams per 30 kg. of seed.
Downy mildew, kevda (Sclerospora sorghi, Kulk, Weston and Uppal): The disease is noticed on young leaves the lower surface of which is covered with downy white growth. Later the leaves become shredded. The disease prevails during August and September. The control measures include rouging, burning of affected plants, proper method of rotation, and growing of resistant varieties.
Ergot, chikta (Claviceps microcephala, wall, Tal): The grains in the ear-head are transformed into black bodies called sclerotia, which contain a poison called ergotin. This poison is fatal to cattle and human beings also. The disease occurs in the middle of August and September. The grains may be soaked in water. The sclerotia and light grains which float may be removed and burnt. Only the steeped
grains may be used as seeds. Deep ploughing may also be practised.
Downy mildew, gosavi (Sclerospora graminicola sacc, schrotes): On young leaves downy white growth mostly on lower surface, with yellowing on corresponding upper surface, is seen. On the ear-heads instead of grains small greenish scale like growth is observed which gives the appearance of green ear. The disease occurs in the months of August and September. It can be controlled by systematic rouging, burning of affected plants, rotation, and growing of resistant varieties.
Wheat: Black stem rust, tambera (Puccinia graminis tritici, Eric and Henn): The disease manifests in the form of reddish brown elongated spots on the leaves and stem. At the maturity of the crop these spots turn black. The infection results into stunted growth of the plants and the consequent reduction in the yield. Sometimes the damage caused by the disease is as high as 66 to 70 per cent. The disease generally occurs from November to February. It can be controlled by growing resistant varieties like Kenphad-25, MED-345, KCN, HY-65, NI-917, NI-315, NI-146, NI-234-5, NI-28 and NI-62 for irrigated crops and selection 59 and 125 for non-irrigated crops.
Loose smut, kajali (Ustilage triciti, Pers, Roster.) : The disease occurs during January and February when ear-heads are formed. Every part of the ear-head except the rachis and awns is affected and loose blackish powder is formed in place of grains. This powder consists of the spores of fungus. The disease can be controlled by soaking the seeds in cold water from 8 to 12 in the morning sometime during the first fortnight of May and spreading them on galvanised iron sheets for drying in the hot sun for four hours and treating them with either D.D.T. or B.H.C. powder.
Foot rot, mulkujwya (Fusarium mouiti, forme): The pathogen attacks at the collar region of the plant which wilts and dies. The disease occurs at any time during the growing period of the crop. It can be controlled by treating the seeds with organic mercurial compounds containing 1 per cent active mercury at the rate of 2-3 grams in one kilogram of seeds. Deep ploughing may also be helpful.
Of pulses: Tur: Wilt, mar (Eusarium oxysporium, F. udum): The disease occurs at any time during the growing season of the crop. It is brought about by fungus dwelling in the soil. The leaves of the affected plants drop down and the plants also wither. If the roots of the affected plants are split open, brown discolouration of the vascular tissue is seen. The damage may range upto 50 per cent. There are no assured measures to control the disease. Hence the alternative course is to sow the resistant varieties.
Of oil-seeds: Groundnut: Tikka (Cercospora arachidicola, Hori: Cercospora personata, Berks and Curs): The disease prevails during August and September. Its first sign is the appearance of conspicuous
round purplish brown spots. The spots later on expand in size and become blackish in colour. Cercospora arachidicola causes formation of irregular circular black spots, often confluent, varying in size from 1 mm. to 1 cm. and surrounded by a yellowish zone, blending into the green. When mature, the conidiosphores emerge out on the upper surface exclusively. The spots caused by cercospora personata are more or less circular, varying in size from 1 mm. to 7 mm., dark brown to black in colour. The spots are surrounded by a bright yellow halo on the upper surface when matured. The disease is controlled by spraying the crop in the beginning of August with 3:3:50 bordeaux mixture or any copper compound. If necessary, second spraying in the fourth week of August may be given and third spraying, if required, in the third week of September. Besides, it can be successfully controlled by sulphur dusting (200 to 300 mesh) at the rate of 15 lbs. per acre.
Safflower: Wilt, mar (Sclerotia sclerotioum, lib, deary) : The pathogen attacks the base portion of the plant. It withers and wilts. White mycelial growth is seen at the collar region. Black sclerotia are formed on the crown roots and inside the stem. Shredding of cortical tissue of the lower part of stem is observed. Some affected plants do not exhibit the symptoms mentioned above but on maturity flower-heads break off from the stalks. The disease can be controlled by adopting preventive measures such as collection and destruction of infected plant material, deep ploughing and clean weeding.
Of fibres: Of cotton : Anthracnose, kawadi (colletotricum indicum Dastur): The disease appears at the seedling stage during the months of June and July, and after the bolls have formed in October and November. At the seedling stage the disease causes seedling rot, i.e., ' cotton rot'. If it appears at the time of boll formation black depressed circular spots appear on the bolls which become yellowish from inside due to spore formation. Attack on the bolls results in stunted growth of the plants and discoloured lint which fetches lower price in the market. The disease can be controlled by destroying the affected debris, by sowing healthy seeds and by treating the seeds with organic mercurial compound containing 1 per cent organic mercury, at the rate of 2 to 3 grams for one kilogram of seed.
Black arm or angular leafspot, tikkya or karpa (Xanthomona malvacearum, Smith, Dowson): The disease occurs on rain-fed crop in July and December, and on irrigated crops in March. The disease first manifests as small water-soaked areas on leaves which are angular in shape. These spots later coalesce involving longer areas of the leaf. The petioles, stem and bolls also get affected. Mature bolls, when affected, open prematurely and the lint from such bolls gets yellow stains. The American cotton variety is highly susceptible. The disease
can be controlled by growing resistant varieties, by treating the seeds with organo-mercurial compound, and by spraying the crop with bordeaux mixture 3:3:50, two to three times during the life of the crop.
Of sugarcane: Whip smut, kajali or chabuk kani (Ustilago scitaminea, Sydow): The affected cane produce whip-like structure covered with thin silvery membrane containing black masses of spores. The disease prevails from January to March. It can effectively be controlled by uprooting and burning the affected canes. As soon as a whip is detected it must be carefully removed without allowing the spores to shed on the neighbouring canes. The improved variety of cane, viz., Co-775 is reported to be resistant to the disease.
Grassy shoot, gavatal wadh: The infected plants are conspicuous and appear with typically stunted mass of small shoots bearing chlorotic, small straight leaves. Secondary infection shows formation of numerous tillers at the base of the shoot. The disease occurs throughout the growing period of the crop.
Of fruits : Grapes : Anthracnose, karpa (Cleosporium ampelophagum, pass, sacc): The disease manifests on vines, stems and young shoots as deep-seated elongated necrotic lesions dark to the border and pinkish white in the centre. The bark on the shoot is finally destroyed and the underlying wood turns grayish. On leaves black circular spots with grey white centre develop and later on such leaves due to drying of the affected portion get twisted and fall down. Premature young blossom when affected shows blighting effects. Severely-affected berries finally dry up and fall down.
The disease generally occurs from June to November. Spraying of bordeaux mixture, 5:5:50, in the third week of May, October and in the last week of July and November controls the disease. Spraying of copper oxychloride or fungicide, 0.5 per cent, i.e., 500 grams in 300 litres of water also controls the disease.
Powdery mildew, bhuri (Unicirula necator, schw, Burr): In the beginning the disease shows whitish mycelial growth irregular in size and shape on both the sides of leaves. The infection spreads rapidly during warm and humid cloudy weather to all green portions of the vine which turns blackish grey and then shows wilted appearance. Black patches are seen on shoots near base. The affected inflorescence fail to set fruit. The affected young berries drop off. The disease usually gains strength during the period between November and January. The infection takes place through spores which are carried by wind from diseased plants to healthy ones.
The disease can effectively be controlled by dusting 300 mesh sulphur in three consecutive dustings. The first dusting is given when the new growth is 15-20 cm. in length at the rate of 22 kg. per hectare. The
second dusting is given at the time of flowering at the rate of 32 kg. per hectare. The third one of the same quantity of 32 kg. is given 20 to 30 days after the second dusting. There is no need to give any more dustings but if it rains
within a day or two after a dusting it may be repeated. A special dusting may be given after pruning in April.
Downy mildew, kewda (Plasmopora viticola, Berk and Curt, Beri and Toni): The disease first appears on tender leaves and twigs. Some faint yellowish green translucent oil spots develop in-between the vein portion on the upper surface of the leaves. Under humid conditions white downy growth is found on corresponding side of under-surface of the leaf spots. The cells in the affected leaf portion die and turn reddish brown. Such leaves finally dry up and fall down. The affected shoots and tendrils show a water-soaked and swollen appearance and later on they are covered with downy growth of fungus. The flowers and young fruits are also affected. They wither, turn brown and finally drop off. The disease occurs between June and September. It can be controlled by spraying bordeaux mixture 5:5:50 in the third week of May and October and also in the first week of July and November. The spraying of copper oxychloride 500 gm. in 200 litres of water also helps in controlling the disease.
Citrus fruits: Citrus canker, devi rog: The disease affects all the aerial parts of lime. Some raised corky spots, orange to brownish in colour, appear on the plant. These spots are more conspicuous on leaves and fruits. They disfigure the fruits. Usually the disease prevails from April onwards. It can be controlled by pruning out the affected twigs and by spraying the plants with bordeaux mixture 5:5:50
Gummosis of citrus, dinkya: The disease usually affects mosambi during the monsoon season. It is characterised by the copious exudation of a resinous gummy substance and the longitudinal cracking of the bark for a considerable distance upwards from the bud union. In its advanced stage there may be extensive shedding of bark exposing the wood below. This is followed by the yellowing and dropping of leaves. The fruit is also affected in wet or damp weather. Some oily spots appear on the surface of the fruit. The spots increase rapidly in size and cover the entire fruit. Various measures can be applied to control the disease. The grafting of mosambi may be done on resistant stock like jamburi at least six inches above the ground. The earth at the base of the trunk may be removed and piled into small encircling mound so as to prevent both soil and irrigation water from coming into direct contact with the trunk and especially the bud joint portion. The bark on the affected portion may be removed carefully. The wound may be covered with 25-30 per cent creosote oil.
Of vegetables: Of tomato: Fusarium wilt, mar (Fusarium oxysporum ffycoper, sici, sacc, Snyder and Hansen): The lower leaves of the affected plants become yellow. It is followed by withering and then wilting of younger leaves. These symptoms may be seen on one or the other branches. After some days, browning of the vascular system may be seen in cross-section of lower root. The disease usually occurs from September to November. It can be checked by growing wilt-resistant varieties.
Early blight, karpa (Alterneria solani Ell and Mart, L. R. Jones and Grout): The disease first manifests as small spots on the leaves. The spots are usually circular dark brown to black in colour. They vary in size from a pin-point to 4 mm. in diameter. If the spots are numerous, they form rings. The leaves then wither and drop off. The stem of the affected plant bears sunken necrotic spots. They are injurious especially when they are at the juncture of stem and side branch. They weaken the branch which later breaks off when fruits develop. Fruits are also infected at both the stages, green and ripe. The disease prevails during July and August. It can effectively be controlled by spraying 50 per cent metallic copper compound or by copper oxychloride at the rate of 500 gm. in 200 litres of water per acre.