Sugarcane diseases are constraints to crop production all over the world, and no country is protected to the destructive influences of plant pathogens and pests. More than 125 diseases of sugarcane caused by fungi, bacteria, viruses, phytoplasma and nematodes have been reported from all over the world (Rottet al., 2000). In spite of all the efforts of breeding for disease resistant varieties, this crop is becoming more and more prone to many diseases and pests.The disease incidence is increasing at an alarming rate and the yield is falling down every year.As per the ISSCT report, every year sugarcane diseases cause the loss of several millions of dollars.
About 10-15% of the nations sugar produced are lost due to diseases. Among them red rot, smut, wilt and pineapple disease (sett rot) are the important fungal diseases. Bacterial diseases like leaf scald disease (LSD) and ratoon stunting disease (RSD) are found to cause considerable yield loss in some countries. Also gumming disease and red stripe are known to cause damage in certain regions. Among the viral diseases mosaic is prevalent in almost all the countries however its severity is felt more in American continents. Besides these, grassy shoot caused by phytoplasmas is also a potential disease, which can cause considerable damage to sugarcane production in several Asian and African countries.
In addition, newly recorded yellow leaf disease (YLD) has become a major constraint in many countries. Foliar diseases such as yellow spot, brown spot, brown stripe, eye spot, ring spot, rust etc may cause loss to sugarcane depending on the prevailing environmental conditions. Many promising varieties were removed from cultivation in the past since they succumbed to new pathogenic variants with more virulence. Also slow build up of many non-fungal diseases in sugarcane causes decline in varietal performance and results invarietal deterioration. In this lecture important diseases of sugarcane and their management are briefly described for the understanding of the extension workers involved in sugarcane development.
It is one of the most widespread sugarcane diseases in the country and it has been a constraint for the past 100 years in India and other South Asian countries. First large-scale destruction of the cane in India by the disease was noticed in Godavari delta of then Madras Presidency on the cultivar Red Mauritius during 1895 to 1899. The disease is responsible for the elimination of many commercial varieties in India in the earlier decades. Epidemics of the disease have been very common ever since its occurrence in India. It was involved in the failure of important commercial varieties like Co 312, Co 419, Co 453, Co 658, Co 997, Co 1148, Co 6304, Co 7805, CoC 671,CoC 85061, CoC 92061,CoJ 64,CoLk 8102, CoS 562, CoS 8436, CoSe 95422 etc.
The epiphytotic nature of the disease was noticed in the subtropical regions of the country till 1970s and later the pathogen got a foothold in the tropical region and is presently in a devastating form in many parts of the Peninsular India particularly in Coastal Andhra Pradesh, Orissa and Tami Nadu. Currently the disease occurs in all the sugarcane growing states in India except Karnataka and Maharashtra states.The disease is caused by the fungal pathogen Colletotrichum falcatum Went. Disease infection seriously affect crop productivity since infected stalks become unfit for milling and partial infection also affect the quality of canes due to inversion of sucrose to reducing sugars. In the advanced stages entire stool dries up. When such canes are split open longitudinally they show reddened areas with horizontal white patches.
The entire parenchymatous tissues are affected and in later stages they form a hollow cavity with dark grey mycelial growth of the fungal pathogens. On the rind, dark brownish lesions of various sizes can be seen. Similarly necrosis on nodal region is also commonly observed. In such canes cut ends show reddening with white patches.The disease is primarily transmitted through infected setts. The secondary spread of the disease occurs during monsoon period when high humidity condition prevails. Sporulating conidia at the nodal portion of the susceptible canes are carried through rain splash and irrigation water to the adjoining cane/area resulting in secondary spread. Fresh surviving debris of red rot inoculum also serves as a source for further spread of the disease.
The disease is cosmopolitan in distribution and at one time or another it has been important in all the sugarcane growing countries. The disease caused severe yield loss to sugarcane for long time in Maharashtra and Northern Karnataka regions till Co 740 was under cultivation. Replacement of Co 740 with Co 86032 and Co 94012 reduced the smut severity in these regions. Currently the disease occurrence is noticed in low intensities in Co 7219, Co 7527, Co 8011 etc in these regions. Widespread cultivation of CoA 92081 resulted in severe outbreak of smut in Andhra Pradesh state.Recently introduction of new varieties has resulted in occurrence of the disease in Southern Karnataka also. Similarly severe smut is noticed on Co 86002 and CoSi 95071 in Gujarat in tropical region.
The disease also causes severe yield losses in many African countries. Severe smut infection severely affects the cane yield and sugar recovery. The yield loss due to the smut could be up to 50 percent in sugarcane.In addition to loss in cane tonnage due to reduced number of millable canes, the disease infection reduces sugar recovery. The severity will be worse in the ratoons.The disease is caused by the fungus Sporisorium scitamineum(Syd.) M. Piepenbr., M. Stoll & Oberw. 2002(Syn: Ustilago scitaminea H. & P. Sydow). The fungus has no alternate hosts. Disease affected stools give out excessive tillers which are lanky and end up with black whip structures. Affected clumps show profuse tillering with lanky tillers.
Occasionally whips are produced from axillary buds also.The infected plants within a field often arise from planting systemically infected setts or from ratoons of infected clumps of previous crop. The disease is very well adapted to aerial dispersal and spread. Smut is generally favoured by hot dry weather conditions. High rainfall reduces the severity of smut development. Disease severity usually increases through ratoon crops. Plant stress increases frequency of whip development; cultivars that normally would not have whips may show symptoms under high stress.
Wilt has caused significant losses in India where several epidemics have occurred. It is responsible for the elimination of many popular varieties from cultivation. Wilt is very common in certain locations where conducive environment and susceptible hosts are available (Viswanathan, 2013a). In most of the delta regions endemic nature of the disease prevails. The disease adversely affects germination. Wilt incidence is always higher in ratoon crops compared with the plant crop. Besides yield reduction, wilt disease also causes 14.6- 25.8% reduction in juice extraction and 3 to 20 percent in sugar recovery due to deterioration in juice quality. Combined infection of red rot and wilt causes more loss to the crop than their infection alone.
Fusarium sacchari (E.J. Butler) W. Gams is the disease causative fungi. The affected stools turn yellowish and finally dry as in the case of red rot. Longitudinal splitting of the affected cane shows dull brownish discolouration of internal tissue with linear pith cavities and desiccation. Wilt fungi are weak soil borne pathogens.Abiotic factors like drought, waterlogging, drought followed by water logging weaken the root system and predisposes the plant for wilt infection. Subterranean soil pests such as white grub, root borer and nematode and insect pests like mealy bug, scale insect, fungal pathogen like red rot weakens the plant and root system paving the way for wilt infection.
Sett rot (Pineapple disease)
Sett rot is caused by the fungal pathogen Cerotocystis paradoxa. The disease is common in germinating setts. The disease is primarily spread through soil borne inoculum under illdrained conditions. The fungus infects the setts mainly through the cut ends and slowly spreads to the entire parenchyma tissues. Sett rot infected setts fail to germinate leaving many gaps in the field. In the early stage of rotting stinky odour of pineapple is emitted due to production of ethyl acetate and it helps in identifying the disease.
The disease is caused by the xylem limiting bacterium Leifsonia (Clavibacter) xyli subsp. xyli (Lxx) (Davis et al.). Diseased clumps usually display stunted growth, reduced tillering, thin stalks with shortened internodes and yellowish foliage. The characteristic stunting and unthriftness associated with RSD are usually greater when there has been a growing period with moisture stress. The sugarcane varieties vary in their tolerance to the pathogen infection.
Growth of a disease crop is slower than that of a healthy crop, and ultimately the yield is reduced. The reduction in yield is due to the production of thinner and shorter stalks rather than a reduction in the total number of canes. The affected plants may not show any abnormality in the root system or in the underground buds and portions of the stalk. In general the disease severity is more in older varieties. The term ‘ratoon stunting’ is misnomer since the disease also causes severe damage in plant crops.Diseased stalks of some varieties may exhibit an internal discolouration of vascular bundles at the lower portion of nodes, but these symptoms are often ephemeral.
They appear as yellow to reddish brown dots, commas, or short lines when viewed by slicinglongitudinally through nodes. The range of colours includes yellow, orange, pink, red and reddish brown and these colours usually stand out in marked contrast to the light-coloured ground tissue of the node. The discolouration does not extend into the internode unlike similar symptoms due to other diseases. The discoloured strands should be found right through the node, and all nodes in the fully developed part of the stalk should show some symptoms. The disease is mainly transmitted through infected setts and survives in the left over debris/soil.
The disease is caused by Sugarcane grassy shoot (SCGS) phytoplasmas. It occurs throughout the country and its severity is more in the areas where proper seed nursery Infected stools show excessive and stunted tillers with narrow leaves. Most of the tillers do not develop into millable canes. In the affected clump, the few canes formed and are stunted with leaves being yellow or white. In some cases, axillary bud sprouting with yellow or paper white leaves may be seen. The whole infected stool appears like a big bunch of grass. The disease is mainly transmitted through infected setts. GSD can cause very heavy yield loss particularly when planting material is obtained from infected sources. The disease severity will be more in ratoon crops and this contributes to poor yield in ratoons.
This is one of the oldest diseases recorded in India and is associated with varietal degeneration. Sugarcane mosaic virus (SCMV) and Sugarcane streak mosaic virus (SCSMV) cause mosaic disease in sugarcane in India. The virus has abundant variation and a single strain can infect sugarcane, maize and sorghum. Symptoms of mosaic may vary in intensity with cultivar, growing conditions, temperature and strain of the virus. The chlorotic areas are most easily seen in young, rapidly growing leaves, particularly near the basal portion of the leaf.
The proportion of the leaf that is covered by the chlorotic areas may vary from scattered, short yellowish stripes to chlorotic areas that predominate over the leaf with islands of normal green. On older leaves, the symptoms tend to recover and appear as healthy.The virus causes mild mottling in the leaves with dark and light areas of chlorophyll development. With more virulent strains, stunting, yellowing, chlorosis and sometimes necrosis are also noticed.
Recently we found that infection of debilitating strains affects yield and quality in sugarcane (Viswanathan and Balamuralikrishnan, 2005). Generally long chlorotic streaks alternate with the normal green portions of the leaf are observed in different varieties in the country.Primary transmission takes place through infected setts. In the field aphids transmit the virus. Although mild strains of mosaic are reported to prevalent in India the causative virus(es) in combination with other pathogens associated with RSD and YLD cause severe yield loss.
Yellow leaf disease (YLD)
This disease is caused by Sugarcane yellow leaf virus (SCYLV) and reported in India during 1999 (Viswanathan, 2002). In addition to SCYLV, Sugarcane yellow leaf phytoplasma (ScYP) also reported to be associated with the disease. The symptoms appear initially on matured leaves three through five usually in maturing plant or ratoon crop. The symptoms could be very clear after 5 to 6 months of crop growth. On the leaves, the symptom appears as yellowish midrib on the lower surface. The yellowing may be confined to midrib region or the yellow discolouration may spread laterally to adjoining laminar region parallel to midrib upto a distance of 2.0 cm. Reddish to pinkish discolouration of midrib and laminar region is also noticed in certain varieties.
In most susceptible varieties, typical yellowing of midribs and laminar region is noticed on upper surface of the leaves. Finally symptoms of necrosis of discoloured laminar region from leaf tip to bottom and subsequent drying of entire leaf is noticed. In ratoon crop, the intensity of the disease will be much higher than in plant crop. The disease incidence in sugarcane is found aggravated by the poor maintenance of the crop in the field. It is observed that infestation with internode borer, flowering, drought conditions, Striga infestation, and infection with other pathogens such as ratoon stunting, grassy shoot etc favour early expression of the disease.
The sugarcane varieties showing mild symptoms usually record normal cane growth. In severely infected clumps cane thickness and stalk height are significantly affected. Severe infection of the disease leads to shortening of internodes in the top. This effect culminates in bunching of leaves at the top. Usually such infection results in drying of entire clumps. Severe infection of SCYLV leads to reduced juice quality and sugar recovery. Combined infection of SCYLV and ratoon stunting bacterium in sugarcane causes severe stunting than their infection alone (Viswanathan, 2002; 2004). The disease occurs in epidemic form on most of the cultivated varieties and it adversely affects cane productivity in the tropical region. The disease infection may result in 25-30 % loss to cane and juice yield in popular varieties (Viswanathan, 2012).
Recently assessing impact of the virus infection on physiological parameters viz. photosynthetic rate (A), stomatal onductance (gs) and SPAD meter values revealed significant reduction in sugarcane cultivars. Virus-infected varieties recorded significant reductions in growth/yield parameters, such as stalk height, stalk thickness and number of internodes. Plant growth reductions were found to be 42.9, 42.3 and 38.9% in YLD-susceptible varieties CoPant 84211, Co 86032 and CoC 671, respectively. In addition to reductions in stalk weight, height and girth, YLD also reduced juice yield in the affected canes up to 34.15% (Viswanathan et al. 2014). Primary transmission of the disease occurs through infected setts. Secondary transmission is achieved through aphid Melanaphis sacchari. Planting of infected setts would result in cent per cent expression of the disease in the field and build up of high virus titre in most susceptible varieties causes severe foliage drying during late maturity stages of the crop.
Sugarcane pathogens like SCMV, SCSMV, SCYLV, SCGS-phytoplasmas and ratoon stunting bacterium systemically infect sugarcane and over the years the varieties degenerate due to the systemic colonization of these pathogens (Viswanathan, 2012, 2013b). Decline in varietal performance over the years is mainly due to accumulated pathogens inside the stalk affecting cane growth and photosynthetic efficiency, which directly results in reduced cane yield and sugar yield. Although these viral/ bacterial pathogens cause limited symptoms in the field, continuous vegetative propagation results in enhanced pathogen load that would increase the pathogenic potential to cause disease.
Combined infection of two or more viral/ bacterial pathogens accelerates the damage to the crop in the field and this is due to infection of one pathogen makes the plant more susceptible to another. In this way, a variety degenerates faster and its potential comes down over the years. Author has witnessed such degeneration in a popular cv Co 419 in Karnataka state due its high susceptibility to mosaic, YLD and RSD. Similarly cvCoC 671 another popular variety of tropical region degenerated
Top rot (PokkahBoeng)
The disease is common during rainy months in the field. Although under normal situations it may not cause significant yield loss it has the potential to arrest the crop growth temporarily. The disease occurs throughout the world and severe forms of the disease are recorded in high humidity areas. Fusarium verticillioides is the causative fungus (Teleomorph:Gibberella fujikuroi (K. Sawada) H.W. Wollenweber). The disease manifests in two phases viz. pokkahboeng and top rot. The most common symptom is a malformed or twisted top, which gives this disease its name “pokkahboeng” from the Javanese language.
Symptoms develop during rainy periods which coincide with grand growth period. Initially, young leaves are chlorotic at their base and patchy elsewhere on the blade. Chlorosis is most obvious on the lower surface of the leaf or in twisted laminar regions, where white mycelium may be seen. Affected leaves tend to be narrow at the base. Development of further symptoms is dependent on the susceptibility of the variety and on environmental conditions conducive to the pathogen. Young leaves may become infected in the spindle, resulting in pronounced wrinkling, twisting and shortening of the leaves. Sometimes the leaves are shortened to few inches without lamina having malformed midrib or growth of the leaves ceased to few inches without malformation giving a de-topped spindle.
As the leaves mature, irregular reddish stripes and specks develop within the chlorotic areas. Infection in the spindle may reach the growing point and continue into the stalk (Viswanathan, 2012). Sometimes the growing point is killed leading to development of top rot. Due to death of spindle, sprouting of the lateral buds occurs. Most of the pokkahboeng-infected canes generally recover from the symptoms but in top rot recovery is not there. Upon recovery we notice the normal whorl with remnants of twisted leaf portions of affected leaves still twisting around the spindle.This disease is favoured by warm, moist growing conditions. Symptom development begins early in the rainy season which normally coincides with rapid and vigorous growth of the canes. The three to seven months-old are most susceptible to the disease. Conidia are air borne and are deposited on plants, then washed by rain into infection sites.
The foliar diseases such as rust, eye spot, yellow spot, brown stripe and ring spot are air borne and most of them survive on other collateral and weed hosts. None of the foliar pathogens are sett-borne. High moisture or relative humidity following rains accompanied by low or cool temperatures favours their incidence. During this period, excess irrigation and non-stripping off their lower leaves and dry leaves, leading to high relative humidity build up within the crop. Such microclimatic conditions help to build up of the disease to epidemic levels. Among the different foliar diseases, rust has become more severe and occurs in epidemic form in Maharashtra and Karnataka during post monsoon season. Almost all
the varieties under cultivation such as CoM 0265, CoVSI 9805, Co 86032, Co 92005, CoC 671, Co 94012, etc were affected by rust. The newly introduced variety CoM 0265 shows high susceptibility to brown spot in Maharashtra and Karnataka.
Integrated disease management
The various types of diseases on sugarcane determine the quality, quality and stability of crop yield. This long duration cash crop due to its vegetative propagation, high sugar accumulation and practice of ratooning makes it easily susceptible to the diseases in the field. Besides this, wide spread practice of monoculture and heavy wet condition add to its susceptibility. This unfavourable environment in host plant invites large number of pathogens. The pathogens are not only reducing the yield but also cause the deterioration of the variety due to their accumulation in the stalk over the time.
This phenomenon is referred to as varietal degeneration and this result in loss of full potential of a variety and subsequently such varieties are withdrawn from cultivation. In the past and even today many high yielding, high sugar and popular cane cultivar like Co 419, Co 740, CoC 671 etc are being withdrawn from cultivation only because of their high susceptibility to red rot, smut, grassy shoot and mosaic. No single method is efficient / available to control sugarcane diseases due to various reasons hence an integrated approach involving cultural, chemical/physical methods, host resistance and legislative measures is suggested for the sustainable management of sugarcane diseases (Viswanathan and Padmanaban, 2008).
Easily available options
Infected planting materials are responsible for the primary spread of the disease in the field. Hence, going for the disease-free setts would reduce the risk of disease introduction to disease free areas. Lack of awareness on seed cane health and ignoring quarantine regulations resulted in introduction of diseases, their epidemics and varietal degeneration in the country. To increase sugarcane productivity, supply of healthy seed canes is to be ensured in the field. As vegetative propagation in sugarcane favours harbouring of the pathogens causing red rot, smut, wilt, grassy shoot, leaf scald, YLD and RSD in the setts, adequate care should be taken while selecting seed canes.
Since it is difficult to detect incipient infections of C. falcatum in seed-pieces, it is recommended to take the planting material from a disease free crop. Any crop with more than 5% smut or as high as 2% grassy shoot incidence is unsuitable for seed purpose. For red rot, if there is any infected clump in the field the plot is to be rejected for seed. It is advised to select always a disease free area to raise the seed crop. Next to healthy seed, sanitation is important in preventing healthy cane from becoming infected with pathogens. Left over sugarcane debris is the prime substrate for the survival and spread of pathogen inoculum especially in the case of red rot, wilt and ratoon stunting. Red rot-infected debris is found to readily infect planted setts and cause death of settlings.
Destruction of all plant debris such as cut canes, trash and stubble in situ is essential for the reduction of the pathogen inoculum. Further, complete removal of the disease-affected clumps in the field would also ensure disease free field. Many of the diseases in sugarcane are aggravated by various biotic and abiotic factors. Negligent crop faces different biotic and abiotic factors like different borers, sucking pests,drought or water logging etc. Biotic factors such as infestation of internode borer or Striga favours early expression of YLD. Hence, all these biotic stresses are needed to be minimized to reduce the severity of YLD. It is well known that root borer infestation favours wilt outbreaks in different regions. Hence, adequate care should be taken to minimize many of these biotic and abiotic factors which predispose the crop for the infection of different pathogens.
Disease surveillance and Diagnosis of sugarcane diseases
Taking preventive measures immediately on noticing the disease occurrence is the best way of avoiding any major outbreaks of the diseases. When due attention is not paid during the first infection stage it would lead to its eventual spread and thereafter attaining epidemic proportion. Many of the diseases do not cause diagnosable symptoms on the seed cane and different factors influence disease expression in the field hence we need to follow certain diagnostic techniques based on serology or molecular biology to detect them in the seed cane before planting in the field. Effort to detect and diagnose sugarcane pathogens using more advanced laboratory techniques has been achieved in the past two decades. Molecular-based diagnostic tests are generally considered to be very sensitive and this is probably their biggest advantage.
Research personnel and development workers should be actively involved in creating awareness on supply of healthy seed. In addition to detecting sugarcane pathogens in seed canes, the recent approaches in the disease diagnosis using serological and molecular approaches have applications in the field of developing disease-free seedlings, disease surveillance and integrated disease management in sugarcane. Since sugarcane is propagated through vegetative cuttings and this favours spread of diseases through planting materials. Primary transmission of different diseases through seed canes poses serious threat to sugarcane growth and performance.
There is a need to diagnose of pathogens in sugarcane setts for effective disease management practice. Also diagnosis is important for the identification of pathogens, breeding crops for resistance to pathogens and epidemiological studies. Biological, physico-chemical, protein and nucleic acid based methods are available for detection of different pathogens. Of these, serological (protein) and nucleic acid based methods offer more reliable and sensitive methods for detection. Among serological methods, various forms of enzyme linked immunosorbent assay (ELISA) have become very popular and largely used for routine detection of pathogens in sugarcane. Tissue-blot technique is also equally effective for the detection of ratoon stunting bacterium and SCYLV.
Among different nucleic acid hybridization based methods, dot blot is more suitable for large scale testing of samples. Polymerase chain reaction (PCR) is the most sensitive method (102-105 times more than ELISA) available presently for the detection and is important in sugarcane viruses occur at low concentration. PCR technique has the potential to detect more than one pathogen in one reaction and diagnosis is also amenable to automation. Various forms of PCR such as DNA-PCR, RT-PCR, IC-PCR, real time quantitative PCR and multiplex PCR are becoming more popular for detection of pathogens in sugarcane. Studies are in progress to develop diagnostic kits based on tissue blot, dot-blot, ELISA, NASH and RT-PCR for the different non-fungal diseases of sugarcane at this Institute. Detailed studies conducted over the years at SBI, Coimbatore resulted in standardizing molecular diagnosis of different pathogens infecting sugarcane.
Plant Pathology lab at SBI is an accredited lab for indexing four viruses and one phytoplasmain sugarcane tissue culture seedlings. Currently, PCR technique is used to index sugarcane materials for GSD infection and RT-PCR technique is used to index sugarcane for SCMV, SCSMV and SCYLV infections.These diagnostics tests have become imperative to raise disease-free planting materials. Hence tissue culture production units in the country are utilizing the indexing service from our lab, which is an accredited test laboratory (ATL) for sugarcane virus testing in the country. The molecular tests are highly sensitive to detect very low virus titre in in vitro stock culture or in seedlings. Utilization of these molecular techniques will be a boon to raise disease free planting materials for sugarcane plantations. There is also possibility of maintaining the popular varieties for many years without degeneration to sustain higher productivity
We notice more damages caused by the diseases in ratoons than plant crop due to different reasons. Inoculum level of systemic pathogens causing smut, GSD, LSD, RSD, mosaic etc. gradually increases and result in severe expression of diseases in ratoon crop. Combined infection of two diseases such as RSD and mosaic or RSD and YLD adversely affect the crop growth and such effect is more pronounced in ratoons. Also establishment of ratoon crop in the field is severely affected by pathogen infection in plant crop.
Similarly more accumulation of pathogen in ratoons facilitates acquiring higher virulence in the pathogens. The popular sugarcane variety Co 419 lost its prominence due to its susceptibility to RSD, mosaic and YLD. Higher RSD pathogen load favours YLD and entire foliage become yellowish and slowly crop degenerates and dries. This situation was found more in ratoons, due to high pathogen load/vigour. Since multi-ratooning of sugarcane has several advantages it is being followed in many countries. However to sustain sugarcane productivity and to improve ratoon productivity these points are to be given due consideration.
Emerging new diseases
Recently many diseases have emerged as serious ones in different countries. However YLD has as serious disease in different continents. This disease has spread to epidemic form in some varieties. Although mild infections of the disease do not cause much crop loss continuous use of seed from such fields lead to severe disease out break. Similarly, problems of wilt, RSD and GSD have been ignored in certain pockets, as there was no previous history of their severity there. Due to introduction of new varieties or change in cultivation pattern, minor diseases become severe. Hence, we have to keep a constant vigil on the emerging diseases in the region and immediately suitable management practices are to be taken up to avert future losses.
Chemical controls are possible for few of the diseases, particularly those caused by fungal pathogens. Sett rot pathogen survives in the soil. As a prophylactic measure, the setts are to be dipped in fungicide solution to protect the cut-ends from the pathogen. Recent studies at the Institute revealed that sett treatment of Thiophanate Methyl fungicide in combination with biocontrol bacterium Pseudomonas reduces soil borne infection of red rot pathogen surviving in debris. If rust is severe five to six sprayings of Mancozeb (0.2%) between November and March is recommended to control under our conditions. Similarly to control eye spot spraying of copper oxychloride or Mancozeb (0.2%) once in 30 days during initiation period is recommended. Whenever the disease is high, fungicidal application should be sprayed at 18-20 day intervals.
Use of resistant varieties
The use of resistant varieties is the most important means of managing sugarcane diseases in a sustainable way. Although frequent breakdown of sugarcane varieties is a cause of alarm, new varieties with high to moderate levels of resistance to the disease are introduced time to time. Classical example is the performance of Co 86032 in different parts of the country especially in Tamil Nadu, where it occupies more than 80% of the cane plantation. Though the cultivar is susceptible to red rot under artificial testings by plug method, it showed high levels of field tolerance. The cultivar showed high levels of resistance when tested by nodal method, which was reflected in its field tolerance under endemic location. The variety suitably replaced two important commercial varieties CoC 671 and CoC 92061 and the cultivar performed better than these two in sugar recovery at different locations.
The varieties Co 86010, Co 86249, Co 93009, Co 94008, Co 95003, Co 97008, Co 99004, Co 99006, CoV 92102, Co 0118, Co 0238 etc are found to be resistant to red rot (Viswanathan, 2010). Unlike red rot, smut resistance in commercial varieties in the field is quite stable. Most of the ruling varieties are resistant to smut. While advocating sugarcane varieties to a factory care should be taken that there should be a proper varietal admixture in that region. In case of disease outbreaks, the disease spread will be rapid in case of monocropping as there is no barrier to check the disease. Also cultivating a single variety in more than 75% of the area would result in development of highly virulent strain of the pathogen, which may cause more damage to the crop than the existing pathotypes.
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