Bacterial blight of cotton incited by Xanthomonas campestris pv. malvacearum (Smith) Dye is one of the major diseases and causes substantial losses in the cotton crop of Pakistan (Hussain and Ali, 1975; Brinkerhoff, 1977). Losses are especially severe in the Punjab where summer rains favour disease development (Brinkerhoff, 1977). Several cultivars resistant to this disease have been screened in Pakistan (Hussain, 1969, Hussain and Yaqub, 1977; Brinkerhoff and Hussain, 1978a, 1978b). Race 18, the most virulent race so far recorded in the world, has also been reported from Pakistan (Hussain and Brinkerhoff, 1978; Hussain, 1984). It was found that the pathogen could survive for two years in infected leaves placed in the laboratory but it lost its survival within 60 days when buried in the moist soil (Hussain and Fatima, 1982)..

The disease is known to be carried over chiefly through infested seed, plant debris of the infected undecomposed parts of the plant. Water in the form of surface drainage, wind driven rains, sprinkler and surface irrigation and field equipment carry the bacterial from old lesions to new infection sites. Insects may also carry the bacterial from plant to plant. The bacteria enter plant tissues through open stomata, other natural openings and through wounds. The infection of bacterial blight is more sever when the soil temperature is about 20C and remains at this for 2-3 days after planting and when soil moisture approaches saturation. Maximum leaf infection occurs at 35C and 85% relative humidity.

Symptoms:

The disease affects almost all the above ground parts of the plant. On the seedlings, small round water-soaked spots appear on the under surface of the cotyledon during the early seedling stage of growth. The common leaf lesions appear first as minute, water soaked spots on the under surface of the leaves. These spots increase in diameter, first turn brown and then black and form angular dead areas. The spots are then visible on the upper surface of the leaf. Often the disease extends along the edges of veins and then it is termed as “Vein blight” or “Black vein”. Sometimes large dead areas are formed which develop as a result of coalescence of numerous smaller spots. This condition usually leads to the death and shedding of the leaves. Black-elongated lesions occur on the young stems, sometimes causing girdling and death of the stem. This type of symptom is known to be of “Black-arm”. Quite often, severely affected stems show deep cracks and gummosis due to which they are liable to break off by wind. The bolls may be affected at any stage of their development. The disease appears first as small, round, water-soaked, raised spots. The lesions gradually become irregular in shape, turn brown to keep black in colour and depressed in the centers. They may remain small or cover the entire boll, penetrating deep into the interior. Saprophytic organisms may attack the infected bolls and complete the rot.

Control:

Seed may be selected from such areas where crop remained free from this disease. Northern areas of the Punjab usually receive less rains as compared to Southern ones; hence the crop of northern districts of the Punjab and Sindh usually remain free of disease. Seed Certification staff may make advantage of this situation and procure the seed from disease free crop of these areas.

Two to three years crop rotation will be helpful for breaking the cycle of the disease (Table-1).

After final picking, the plant debris of the infected crop should be ploughed under and irrigate the fields immediately to ensure quick decomposition of the trash (Table-2).

Many seed and seedling diseases have been reported from various cotton growing countries of the world and losses may be very high in certain cases in form of poor stand, stunted growth, decrease in the size of the bolls and inferior quality of produce. Various types of pathogens are known to cause these diseases.

In Pakistan, Khan (1959) isolated a number of micro-organisms including Alternaria, Rhizopus and Aspergillus spp. from fuzzy and acid delinted cotton seed. He also did some preliminary studies on seed treatment of cotton and concluded that Granosan and Spergon were effective in controlling these fungi. Similar studies were repeated in 1966 in Agricultural University at Faisalabad. Field experiments have been conducted at Ayub Agricultural Research Institute, Faisalabad on seed treatment of cotton for 7-8 years but the results obtained were inconclusive.

Studies on seed microflora and seed treatment were carried out by Jagirdar and Kamal (1967) in Sindh and it was found that almost the similar micro-organisms were associated with cotton seed of Sindh. Fusarium spp. was found to the most deteriorative for cotton seed and seedlings under controlled conditions. It was also found that acid delinting and treating seed with fungicides would increase germination and yield of seed cotton. Almost the same studies were repeated by Panhwar and Jagirdard during 1977 with new fungicides. The data of their field surveys indicated that seedling mortality was hardly 1% in the growers’ fields.

Hussain and Yaqub (1976) carried out laboratory studies on microfloa associated with cotton seed and effect of different temperatures, media and chemicals on frequency percentage of the micro-organisms. Mainly, Alternaria spp., Aspergillus spp., Fusarium spp. and some other organisms were found to be associated with fuzzy cotton seed. Vitavax, Captan and Benlate were found to be the most effective fungicides to check the growth of micro-organisms in vivo. Hussain and Tanveer (1981) conducted field surveys to record prevalence of seedling mortality in cotton belt of Pakistan and found 1.7% (average of 15 localities) seedling mortality in the Punjab and that of 1.0% (average of 8 localities) in Sindh. Hafiz (1981) emphasized for compulsory seed treatment in this country to improve seed germination, development of healthy seedlings and to get better stand and increased yield. Kafi (1984) reviewed the work done on seed treatment and showed yield increase due to seed dressing.

Hussain et al (1982) carried out studies on seedling diseases and seed treatment of cotton. They isolated about 2 dozens of micro-organisms associated with cotton seedlings (Table-6). They carried out seed treatment field experiments at Multan by using different fungicides and could found inconsistent results in increasing the germination and yield of seed cotton (Table 7 and 8).

Boll rot of cotton is world-wide in its distribution and the diseases takes heave toll of the crop during hot and humid days of the crop season. The problem of boll rot has become very serious in this country due to planting of early maturing and susceptible varieties. The incidence of the disease has been reported to vary from 5 to 30% in Sindh and 1 to 40% in the Punjab

Many organisms have been reported to be associated with boll rots. Kamal and Naim (1969) found Aspergillus niger, Rhizopus oryzae, Fusarium oxysporum and Xanthomonas malvacearum associated with boll rot in Sindh. They also found that these organisms could not cause rotting without physical injury to the bolls. Boll rot studies were undertaken by Hussain and his associates (1975, 1977) in the Punjab and found about two dozens of micro-organisms associated with cotton bolls (Table 9). On the basis of their virolence and pathogenicity, they were divided into two groups (a) the primary pathogens which can cause boll rotting without physical injury are: Botryodiplodia theobromae, Collectotrichum capasici, Myrothecium roridum and Xanthomonas malvacearum (b) the weak parasites which cannot cause boll rotting without physical injury are: Aspergilus spp., Alternaria macrospore, Fusarium spp., Rhizopus and others.

Symptoms:

Due to large number of micro-organisms causing boll rots, the symptoms vary considerably. In some cases, discoloured, sunken areas developed on the boll surface. In others, external symptoms may be inconspicuous but complete destruction of seed and fibre occurs. Often, infected bolls will open with the locks partially fluffed and stained fibre is knocked to the ground during harvest. When picked and ginned, the stained fibre will result in lower and spotted fibre grades.

Control:

Losses due to boll rots can be reduced by:

• Avoiding practices which promote growth especially application of excessive nitrogenous fertilizer and irrigation. The timing of irrigation water should be corrected and the last watering to the crop should be stopped in first week of October.
• Effective control of late season pests will be helpful in reducing the losses caused by weak parasites.
• Crop should be kept free of weeds and grasses all the time.
• Spraying the crop with Benlate at the rate of 250 g/acre preferably with any compatible pesticide will reduce incidence of boll rots.
• Planting okra-leaf and frego-bract varieties which will permit free penetration of air and light to the plant.

Root rot is one of the serious diseases of cotton in Pakistan. It occurs throughout the cotton growing tracts of this country but is more severe in Bahawalpur and Khairpur divisions of Punjab and Sindh. The incidence of the disease varies from field to field but on an average the disease causes 1.5 to 5.0% loss annually in this country. However, in an individual field, the incidence upto 20 percent has been recorded. This disease has been investigated intensively in this country. Vasudeva and his co-workers (1935-1943), Sattar and Hafiz (1952), Kamal (1958-1964), Kausar (1966), Khan (1952-1962) and Akhtar (1967-1976) made very useful investigations on cause, symptomatology, physiology and control of this disease.

Symptoms:

The first symptom of the disease is sudden wilting, which ultimately results in the death of the entire plant. The diseased plants can easily be pulled out of the soil due to rotting of the entire rootlets. The cap root is shredded. On pressing, a yellowish liquid oozes out of the roots of a freshly wilted plant. The attack starts when the cotton plants are about 7-8 weeks old. It, however, continues to be vigorous throughout the months of July and August. The rate of death of plants gradually declines and the disease almost ceases to appear by the end of September. The disease appears in patches in a field and it remains almost confined to these patches year after year. The most frequently associated organisms are Rhizoctonia solani and R. bataticola, R. solani has been isolated in fairly high frequency in ‘situ’ from the root rot affected soil patches.

Control:

• Inter-cropping cotton with ‘Moth’ (Phaseolus aconitifolius) is very helpful in reducing incidence of root rot. The moths should not be removed from the soil before mid of August. Because the disease appears in already known patches of the soil, therefore, at least, the crop of these patches should be intercropped with ‘moth’ to avoid the disease.
• Deep ploughing removal of root rot infected stubbles and planting cotton late, mid to end of June, in root rot affected fields is recommended.
• Planting resistant varieties is very helpful in controlling of this disease. Our data show (Table 10) that CIM-70 is resistant, NIAB-78 tolerant and other commercial varieties like MNH-93, B-557 and BS-1 are highly susceptible to this disease. It is, therefore, recommended that CIM-70 should be planted in the fields affected with root rot disease.

This disease is caused by Colletotrichum capsici and C. gossypii and is found in fairly high frequency in the cotton growing areas of the Punjab.

Symptoms:

The disease affects the seed, seedlings, branches and bolls. On the cotyledons and primary leaves of the seedlings, it forms small, reddish or light coloured disease rpots. The lesions at the collar are elongated and reddish brown in colour. They may either be one side of the stem or may engirdle it. On bolls the disease appears as small, water-soaked, circular, slightly depressed, reddish brown spots.

Control:

• The disease can be controlled by sowing disease free seed or treating with fungicides, growing resistant varieties and destroying the plant debris of cotton fields.

This disease was reported by Tanveer and Haq (1979) from the Punjab and was found to be of common occurrence in the early planting exotic varieties. Fusarium solani and Rhizoctonia spp. were isolated from stunted plants but the disease could not be reproduced by these fungi.

Symptoms:

The disease may express its effects from seed germination to boll formation. The seed from stunted plant has low germination capacity and reduced vigour. On germination the earliest symptoms are see in one week old seedlings. Appearance of the true leaves is delayed and the plants remain stunted. The colour of the vascular system of the plant remained unchanged which is in contrast to many wild diseases.

Control:

• All local varieties like B-557, MNH-93 and NIAB-78 have high degree of resistance. If at all, any exotic variety is to be cultivated, June sowing is best for this purpose to avoid the disease.

This disease is of common occurrence in the cotton growing areas of the Punjab. It was first recorded on cotton in August, 1973 in the Punjab (Tanveer and Akhtar, 1974; Tanveer et al 1974). The disease is caused by Myrothecium rordum.

Symptoms:

Earliest symptoms are seen in the end of July becoming prominent towards the end of the season. The disease mainly remain confined to the leaves but the bolls are also affected under favourable conditions of the disease spread, small, circular, tan coloured spots with broad violet brown margins surrounded by zones of translucent areas giving the appearance of concentric rings appear on the leaves. These lesions enlarge and elongate, later becoming circular, semi-circular or very rarely irregular in margins. They develop into characteristic spots and after sometimes, pin-head sized structures appear on them. These structures are the fruiting bodies of the fungus.

Control:

• The disease can be controlled through spraying Benlate and Vitigran blue at the rate of 250 grams and 1 kg/450 lit of water respectively.

Cercospora leaf spot is caused by Cercospora gossypina. It usually appears in the months of October and November on the mature leaves.

Symptoms:

The spots are round or irregular in shape, with yellowish brown, purple, dark brown or blackish borders and white centre. There is sometimes coalescing of the adjacent diseased spots. The white centre finally fall off leaving a raged appearance. Severely affected leaves become pale in colour and finally fall off.

Control:

• The disease is of minor importance due to late appearance on the older leaves and generally no control measure is necessary. Desi cotton, Gossypium arboretum, is more susceptible to this disease than American cotton G.hirsutum.

Cotton leaf curl is a virus disease transmitted by whiteflies, Bemisia gossypiperds and B. tabaci. It has caused heavy losses in Sudan previously. In Pakistan it was first observed in 1965. Since then, it was being ob served on occasional plants. Since 1977 its incidence has increased substantially in some areas.

Symptoms:

As the name indicates, the virus causes either upward or downward ourling of the leaves. Veins of the leaves become thickened which are pronounced on the under-side. Two types of vein thickenings are seen. Small vein thickening (SVT) and main vein thickening (SVT). The former being more common. In extreme, but not infrequent cases, formation of the cup shaped or leaf laminar out growths called ‘enation’ appear on the underside of the leaf. Severely infected plants may show twisted appearance of the leaf, petioles, fruiting branches and to lesser extend main stem which tend to grow tall with elongated internodes.

Control:

• The virs has a wide host range. Among the Malvaceae it includes species of Gossypium, Hibiscus, Althaea, Sida, Malva, Malvaviscus and Abutilon etc. The possible means of carryover of leaf curl in the fields are, infected cotton stumps, out of season okra and infected perennial malvaceous and other bost plants.

Plant parasitic nematodes constitutes and important problem for cotton production in many countries of the world/they infect roots and rootlets and produce galls, rots, surface nectosis and lesions. Above ground plant parts remain stunted, yellow and sometimes show symptoms of wilting and dropping of leaves. In the advanced stages, death of the plant may take place.

Research on nematodes of cotton in Pakistan received very little attention. Recommendation on the use of nematicides in cotton were being made based on the symptoms seen on the plants. In depth studies farried out in the plant pathological laboratory at CCRI., Multan (Tanveer, 1976; Tanveer and Haq, 1975) revealed that the population of parasitic news odes in cotton fields was generally low. The most frequently occurring nematodes were Tylenchorynchus sp. and Haplolaimus sp. with a population of 108 and 11.9 per sample of 300 g. soil respectively. Other parasitic nematodes ranged from 1-7 per sample. This population level of parasitic nematodes is not sufficient to cause much damage to cotton plant. Therefore, at present, nematodes in cotton fields, do not pose any serious problem for cotton growing in Pakistan. Whenever nematode symptoms are seen in the field, it is essential to assess the population of nematodes before adopting any control measures.

Regular surveys, however, needs to be carried out for keeping the track of the spread and build-up of nematode population in a locality every year, specially in the area where cotton crop is planted in rotation with sunflower, sugarcane and vegetables.

The disease is caused by macroxyphiella hibiscifolia and other different types of mould fungi like Alternaria. spp. etc

Symptoms:

Sooty-black symptoms appear initially on the midrib on which the glands develop first. The disease goes on spreading with the development of the glands in the other veins. Mould fungi like Alternaria spp. also develop on the honey dews secreted by sucking insects. Such type of moulds cover leaves, branches, stems and flowers. The disease deteriorates quality of fibre if appears late in the season.

Control: