Groundnut Diseases PDF

9. Diseases of Groundnut Tikka leaf spots Early leaf spot: Cercopora arachidicola (Sexual Stage: Mycosphaerella arachidis) Late leaf spot: Phaeoisariopsis personata (Syn : Cercospora personata) (Sexual stage : Mycosphaerella berkeleyii) Symptoms Th...

9. Diseases of Groundnut Tikka leaf spots Early leaf spot: Cercopora arachidicola (Sexual Stage: Mycosphaerella arachidis) Late leaf spot: Phaeoisariopsis personata (Syn : Cercospora personata) (Sexual stage : Mycosphaerella berkeleyii) Symptoms The disease occurs on all above ground parts of the plant, more severely on the leaves. The leaf symptoms produced by the two pathogens can be easily distinguished by appearance, spot colour and shapes. Both the fungi produce lesions also on petiole, stem and pegs. The lesions caused by both species coalesce as infection develops and severely spotted leaves shed prematurely. The quality and yield of nuts are drastically reduced in severe infections. Pathogen C. arachidicola (SexualSymptoms stage: M. arachidis)  The pathogen is intercellular and do not produce haustoria and become intracellular when host cells die. The fungus produces abundant sporulation on the upper surface of the leaves. Conidiophores are olivaceous brown or yellowish brown in colour, short, 1 or 2 septate, unbranched and geniculate and arise in clusters. Conidia are sub hyaline or pale yellow, obclavate, often curved 3-12 septate, 35- 110 x 2.5 - 5.4
m in size with rounded to distinctly truncate base and sub-acute tip. The perfect stage of the fungus produces perithecia as ascostromata. They are globose with papillate ostiole. Asci are cylindrical to clavate and contain 8 ascospores. Ascospores are hyaline, slightly curved and two celled, apical cell larger than the lower cell. P. personata (C. personata) (Sexual stage: M. berkeleyii) The fungus produces internal and intercellular mycelium with the production of haustoria. The conidiphores are long, continuous, 1-2 septate, geniculate, arise inclusters and olive brown in colour. The conidia are cylindrical or obclavate, short, measure 18-60 x 6-10
m, hyaline to olive brown, usually straight or curved slightly with 1-9 septa, not constricted but mostly 3-4 septate. The fungus in its perfect stage produces perithecia as ascostromata which are globose or broadly ovate with papillate ostiole. Asci are cylindrical to ovate, contain 8 ascospores. Ascospores are 2 celled and constricted at septum and hyaline. Favourable Conditions Prolonged high relative humidity for 3 days. Low temperature (20 C) with dew on leaf surface. Heavy doses of nitrogen and phosporus fertilizers Deficiency of magesium in soil. Disease cycle The pathogen survives for a long period in the infected plant debris through conidia, dormant mycelium and perithecia in soil. The volunteer groundnut plants also harbour the pathogen. The primary infection is by ascospores or conidia from infected plant debris or infectd seeds. The secondary spread is by wind blown conidia. Rain splash also helps in the spread of conidia. Management Remove and destory the infected plant debris.  Eradicate the volunteer groundnut plants. Keep weeds under control. Treat the seeds with Carbendazim or Thiram at 2g/kg. Spray Carbendazim 500g or mancozeb 2 kg or Chlorothalonil 2 kg/ha and if necessary, repeat after 15 days. Grow moderately resistant varieties like ALR 1. Rust - Puccinia arachidis Symptoms The disease attacks all aerial parts of the plant. The disease is usually found when the plants are about 6 weeks old. Small brown to chestnut dusty pustules (uredosori) appear on the lower surface of leaves. The epidermis ruptures and exposes a powdery mass of uredospores. Corresponding to the sori, small, necrotic, brown spots appear on the upper surface of leaves. The rust pustules may be seen on petioles and stem. Late in the season, brown teliosori, as dark pustules, appear among the necrotic patches. In severe infection lower leaves dry and drop prematurely. The severe infection leads to production of small and shriveled seeds. Symptoms Pathogen The pathogen produces both uredial and telial stages. Uredial stages are produced abundant in groundnut and production of telia is limited. Uredospores are pedicellate, unicellular, yellow, oval or round and echinulated with 2 or 3 germpores. Teliospores are dark brown with two cells. Pycnial and aecial stages have not been recorded and there is no information available about the role of alternate host. Teliospores Uredospores Favourable Conditions High relative humidity (above 85 per cent). Heavy rainfall. Low temperature (20-25˚C). Disease cycle The pathogen survives as uredospores on volunter groundnut plants. The fungus also survives in infected plant debris in soil. The spread is mainly through wind borne inoculum of uredospores. The uredospores also spread as contamination of seeds and pods. Rainsplash and implements also help in dissemination. The fungus also survives on the collateral hosts like Arachis marginata, A. nambyquarae and A. prostrate. Management Avoid monoculturing of groundnut. Remove volunteer groundnut plants and reservoir hosts. Spray mancozeb 2 kg or Wettable Sulphur 3 kg or Tridemorph 500ml or Chlorothalonil 2 kg/ha. Grow moderatelyresistant varieties like ALR 1. Collar rot or seedling blight or crown rot - Aspergillus niger and A. pulverulentum Symptoms  The disease usually appears in three phases. i. Pre-emergence rot Seeds are attacked by soil-borne conidia and caused rotting of seeds. The seeds are covered with black masses of spores and internal tissues of seed become soft and watery. ii. Post-emergence rot The pathogen attacks the emerging young seedling and cause circular brown spots on the cotyledons. The symptom spreads later to the hypocotyl and stem. Brown discolored spots appear on collar region. The affected portion become soft and rotten, resulting in the collapse of the seedling. The collar region is covered by profuse growth of fungus and conidia and affected stem also show shredding symptom. iii. Crown rot The infection when occurs in adult plants show crown rot symptoms. Large lesions develop on the stem below the soil and spread upwards along the branches causing drooping of leaves and wilting of plant. Pathogen Symptoms The mycelium of the fungus is hyaline to sub-hyaline. Conidiophores arise directly from the substrate and are septate, thick walled, hyaline or olive brown in colour. The vesicles are mostly globose and have two rows of hyaline phialides viz., primary and secondary phialides. The conidial head are dark brown to black. The conidia are globose, dark brown in colour and produce in long chains. Favourable Conditions Deep sowing of seeds. High soil temperature (30-35˚ C). Low soil moisture. Disease cycle The pathogen survive in plant debris in the soil, not necessarily from a groundnut crop. Soil-borne conidia cause disease carry over from season to season. The other primary source is the infeced seeds. The pathogen is also seedborne in nature. Management Crop rotation. Destruction of plant debris. Remove and destroy previous season's infested crop debris in the field Seed treatment with Trichoderma viride / T.harzianum @ 4 g/kg of seeds and soil application of Trichoderma viride / T.harzianum at 2.5kg/ha, preferably with organic amendments such as castor cake or neem cake or mustard cake @ 500 kg/ ha. Root rot - Macrophomina phaseolina Symptoms In the early stages of infection, reddish brown lesion appears on the stem just above the soil level. The leaves and branches show drooping, leading to death of the whole plant. The decaying stems are covered with whitish mycelial growth. The death of the plant results in shredding of bark. The rotten tissues contain large number of black or dark brown, thick walled sclerotia. When infection spreads to underground roots, the sclerotia are formed externally as well as internally in the rotten tissue. Pod infection leads to blackening of the shells and sclerotia can be seen inside the shells. Pathogen The fungus produces hyaline to dull brown mycelium. The sclerotia are thick walled and dark brown in colour. Favourable Conditions  Prolonged rainy season at seedling stage and low lying areas. Disease cycle The fungus remains dormant as sclerotia for a long period in the soil and in infected plant debris. The primary infection is through soil-borne and seed-borne sclerotia. The secondary spread of sclerotia is aided by irrigation water, human agency, implements and cattle etc. Management Treat the seeds with thiram or carbendazim 2g/kg or Trichoderma viride at 4g/kg. Spot drench with Carbendazim at 0.5 g/lit. Rossette - Groundnut rosette assistor virus (GRAV), Groundnut rosette virus and Groundnut rosette satellites Symptoms The affected plants are characterized by the appearance of dense clump or dwarf shoots with tuft of small leaves forming in a rosette fashion. The plant exhibits chlorosis and mosaic mottling. The infected plants remain stunted and produce flowers, but only a few of the pegs may develop further to nuts but no seed formation. Symptoms Pathogen The disease is caused by a complex mixture of viruses viz.,Groundnut rosette assistor virus (GRAV), Ground nut rosette virus and Groundnut rosette satellites is an isometric, not enveloped and 28nm diameter (reported from India) and it gives no overt symptom in groundnut. Groundnut rosette virus is with ssRNA genome, which becomes packaged in GRAV virious and thus depends on it for aphid transmission, but produces no overt symptoms in groundnut. The groundnut rosette satellites are satellite RNAs that control the symptoms and cause the different types of rosette (chlorotic, green and mosaic). Disease Cycle The primary source of spread by aphid vector, Aphis craccivora and A. gossipii in a persistent manner, retained by vector but not transmitted congenitally. The virus is not transmitted by any other means like mechanical or seed or pollen. The virus can survive on the volunteer plants of groundnut and other weed hosts. Management Practice clean cultivation. Use heavy seed rate and rogue out the infected plants periodically. Spray Monocrotophos or Methyl demeton at 500 ml/ha. Groundnut bud necrosis disease - Groundnut bud necrosis virus (GBNV- Tospo virus) Symptoms First symptoms are visible 2-6 weeks after infection as ring spots on leaves. The newly emerging leaves are small, rounded or pinched inwards and rugose with varying patterns of mottling and minute ring spots. Necrotic spots and irregularly shaped lesions develop on leaves and petioles. Stem also exhibits necrotic streaks. Symptoms  Plant becomes stunted with short internodes and short auxillary shoots. Leaflets show reduction in size, distortion of the lamina, mosaic mottling and general chlorosis. In advanced conditions, the necrosis of buds occurs. Top bud is killed and necrosis spreads downwards. Drastic reduction in flowering and seeds produced are abnormally small and wrinkled with the dark black lesions on the testa. Pathogen It is caused by Groundnut bud necrosis virus (GBNV). The virus particles are spherical, 30 nm in diameter, enveloped, ssRNA with multipartite genome. Disease cycle The virus perpetuates in the weed hosts viz., Bidens pilosa, Erigon bonariensis, Tagetes minuta and Trifolium subterraneum. The virus is transmitted by thrips viz., Thrips palmi, T. tabaci and Frankliniella sp. Management Adopt plant spacing of 15x15 cm. Remove and destory infected plants up to 6 weeks after sowing. Application of Monocrotophos 500 ml/ha, 30 days after sowing either alone or in combination with AVP (Anti Viral Principle) extracted from sorghum or coconut leaves. Spray the crop with 10 per cent AVP at 500 lit/ha, ten and twenty days after sowing. Minor diseases Stem rot - Sclerotium rolfsii Symptoms The first symptom is the sudden drying of a branch which is completely or partially in contact with the soil. The leaves turn brown and dry but remain attached to the plant. Near soil on stems white growth of fungus mycelium is appeared. As the disease advances white mycelium web spreads over the soil and the basal canopy of the plant. The sclerotia, the size and colour of mustard seeds, appear on the infected areas as the disease develops and spreads. The entire plant may be killed or only two or three branches may be affected. Lesions on the developing pegs can retard pod development. Infected pods are usually rotted.  Symptoms Management Cultural practices such as deep' covering or burial of organic matter before planting, non- dirting cultivation by avoiding movement of soil up around the base of plants and preventing accumulation of organic debris are extremely useful in reducing the disease. Crop rotation with wheat, corn and soyabean may minimize the incidence of stem rot. Seed treatment with Carbendazim / Thiram / Captan @ 2-3 g/kg seed. Seed treatment with Trichoderma viride formulation (4g/kg) followed by application of 2.5kg Trichoderma viride formulation mixed with 50kg farm yard manure before sowing. Wilt - Fusarium oxysporum and F. solani Symptoms Germinating seeds are attacked by the pathogens shortly before emergence. There is general tissue disintegration and the surface of the seedling is covered with sporulating mycelium. Damping off symptoms characterized by brown to dark brown Water soaked sunken lesions on the hypocotyl which later encircle the stem and extend above the soil level. Roots are also attacked, especially the apical portions. The affected seedlings become yellow and wilted. The leaves turn greyish green and the plants dry up and die. The roots and stems show internal vascular browning and discolouration. These fungi are also commonly associated with pod rot. Management Seed treatment with systemic fungicides like Carbendazim at 2g/kg seed. Anthracnose - Colletotrichum dematium and C. capsici Symptoms  Small water-soaked yellowish spots appear on the lower leaves which later turn into circular brown lesions with yellow margin 1 to 3 mm in diameter. In some cases lesions enlarge rapidly become irregular and cover the entire leaflet, and extend to the stipules and stems. Brownish grey lesions occur on both the surfaces of leaflets. Infection spreads to stipules, petioles and branches. Symptoms Disease cycle The pathogen is seed, soil and air-borne. Management Deep summer ploughing. Use healthy certified seeds. Removal of plant debris. Seed treatment with copper oxychloride at 3g/kg seed or carbendazim at 2g/kg seed. Yellow mould - Aspergillus flavus Symptoms Seed and un-emerged seedlings attacked by the pathogen are rapidly shriveled and dried. Brown or black mass covered by yellow or greenish spores may be seen. Decay is most rapid when infected seeds are planted. After seedling emergence cotyledons already infected with the pathogen, show necrotic lesions with reddish brown margins. This necrosis terminates at or near the cotyledonary axis. Under field conditions the diseased plants are stunted, and are often chlorotic. The leaflets are reduced in size with pointed tips, widely varied in shape and sometimes with veinal clearing. Management Since the fungus is a weak parasite, agronomic practices which favour rapid germination and vigorous growth of seedling will reduce the chance of A. flavus infection. Seed treatment with carbendazim or captan or thiram at 2g/kg seed. Grey mould - Botrytis cinerea Infection is seen on leaves, stem and underground parts of the groundnut. Initially infection occurs at ground level by a light grey fungal rot which causes death of the plants. Bacterial wilt - Pseudomonas solanacearum Infected plants appear unhealthy, chlorotic and wilt under water stress. Dark brown discolouration of xylem is seen. Grey slimy liquid ooze out of the vascular bundles. Leaf spot - Alternaria arachidis and A. tenuissima Symptoms Lesions produced by A. arachidis are brown in colour and irregular in shape surrounded by yellowish halos. Symptoms produced by A. tenuissima are characterized by blighting of apical portions of leaflets which turn light to dark brown colour. Lesions produced by A. alternata are small, chlorotic, water soaked, that spread over the surface of the leaf. The lesions become necrotic and brown and are round to irregular in shape. Veins and veinlets adjacent to the lesions become necrotic. Lesions increase in area and their central portions become pale, rapidly dry out, and disintegrate. Affected leaves show chlorosis and in severe attacks become prematurely senescent. Lesions can coalesce, give the leaf a ragged and blighted appearance. Symptoms Management Foliar application of Mancozeb (2kg/ha) or Copper oxychloride (2kg/ha) or Carbendazim (500g/ha). Indian Peanut Clump Disease - Peanut Clump virus Earlier this disease was confused with groundnut rosstte. Now it is recognized as a distinct virus causing clump disease. The leaves turn very dark and plants become severely stunted. The disease is soil borne and transmitted by a fungus, Polymyxa graminis. The pH of the soil affects transmission. It is also transmitted by seed. The virus is rod shaped, 190-245nm long x 21nm wide, not enveloped, ssRNA genome. Other virus diseases of minor importance occurring on groundnut are: Peanut chlorotic streak (caused by Caulimovirus, occurs only in India), Peanut green mosaic and mottle (caused by a Potyvirus), peanut stunt (caused by Cucumovirus), groundnut chlorotic spot (caused by a Potexvirus), groundnut eye spot (caused by Potyvirus) and groundnut ringspot.  11. Diseases of Sunflower Root rot or charcoal rot - Rhizoctonia bataticola (Pycnidial stage: Macrophomina phaseolina) Symptoms The pathogen is seed-borne and primarily causes seedling blight and collar rot in the initial stages. The grown up plants also show symptoms after flowering stage. The infected plants show drooping of leaves and death occurs in patches. The bark of the lower stem and roots shreds and are associated with a large number of sclerotia. Dark coloured, minute pycnidia also develop on the lower portion of the stem. Symptoms Pathogen The fungus produces a large number of black, round to irregular shaped sclerotia. The pycnidia are dark brown to black with an ostiole and contain numerous single celled, thin walled, hyaline and elliptical pycnidiospores. Favourable Conditions Moisture stress and higher temperature favour development of the disease. Disease cycle The pathogen survives in soil and in infected crop residues through sclerotia and pycnidia. The pathogen is seed-borne and it serves as primary source of infection. Wind-borne conidia cause secondary spread. The soil borne sclerotia also spreads through rain splash, irrigation water and implements. Management Closer planting of the seedling should be avoided. Optimum nutrition should be provided to maintain the plant vigour. Whenever the soil becomes dry and the soil temperature rises then irrigation should be provided. Seed treatment with Trichoderma viride formulation at 4 g/kg seed. In endemic areas long crop rotation should be followed. Treat the seeds with Carbendazim or Thiram at 2/kg Spot drench with Carbendazim at 500 mg/litre. Leaf blight - Alternaria helianthi Symptoms The pathogen produces brown spots on the leaves, but the spots can also be seen on the stem, sepals and petals. The lesions on the leaves are dark brown with pale margin surrounded by a yellow halo. The spots later enlarge in size with concentric rings and become irregular in shape. Several spots coalesce to show bigger irregular lesions leading to drying and defoliation. Symptoms Pathogen The pathogen produces cylindrical conidiophores, which are pale grey-yellow coloured, straight or curved, geniculate, simple or branched, septate and bear single conidium. Conidia are cylindrical to long ellipsoid, straight or slightly curved, pale grey-yellow to pale brown, 1 to 2 septate with longitudinal septa. Favourable Conditions Rainy weather. Cool winter climate. Late sown crops are highly susceptible. Disease cycle The fungus survives in the infected host tissues and weed hosts. The fungus is also seed- borne. The secondary spread is mainly through wind blown conidia. Management Deep summer ploughing. Proper spacing Clean cultivation and field sanitation. Use of resistant or tolerant variety like B.S.H.1. Application of well rotten manures. Practicing crop rotation. Planting in mid-September. Remove and destroy the diseased plants Treat the seeds with Thiram or Carbendazim at 2 g/kg. Spray Mancozeb at 2 kg/ha. Rust - Puccinia helianthi Symptoms Small, reddish brown pustules (uredia) covered with rusty dust appear on the lower surface of bottom leaves. Infection later spreads to other leaves and even to the green parts of the head. In severe infection, when numerous pustules appear on leaves, they become yellow and dry. The black coloured telia are also seen among uredia on the lower surface. The disease is autoecious rust. The pycnial and aecial stages occur on volunteer crops grown during off-season. Symptoms Pathogen The uredospores are round or elliptical, dark cinnamon-brown in colour and minutely echinulated with 2 equatorial germpores. Teliospores are elliptical or oblong, two celled, smooth walled and cheshnut brown in colour with a long, colourless pedicel. Uredospores and Teliospores Favorable Conditions Day temperature of 25.5° to 30.5°C with relative humidity of 86 to 92 per cent enhances intensity of rust attack. Disease cycle The pathogen survives in the volunteer sunflower plants and in infected plant debris in the soil as teliospores. The disease spreads by wind-borne uredospores from infected crop. Management Use of tolerant and resistant varieties Crop rotation should be followed. Previous crop remains should be destroyed. Removal of crop residues Spray Mancozeb at 2kg/ha. Head rot - Rhizopus sp. Symptoms The affected heads show water soaked lesions on the lower surface, which later turn brown. The discoloration may extend to stalk from head. The affected portions of the head become soft and pulpy and insects are also seen associated with the putrified tissues. The larvae and insects which attack the head pave way for the entry of the fungus which attacks the inner part of the head and the developing seeds. The seeds are converted into a black powdery mass. The head finally withers and droops down with heavy fungal mycelial nets. Symptoms Pathogen Pathogen produces dark brown or black coloured, non-septate hyphae. It produces many aerial stolens and rhizoids. Sproangia are globose and black in colour with a central columella. The sporangiospores are aplanate, dark coloured and ovoid.  Structure of Rhizopus Favourable Conditions Prolonged rainy weather at flowering. Ddamages caused by insects and caterpillars. Disease Cycle The fungus survives as a saprophyte in host debris and other crop residues. The disease is spread by wind blown spores. Management Treat the seeds with thiram or carbendazim at 2g/kg. Control the caterpillars feeding on the heads. Spray the head with Mancozeb at 2kg/ha during intermittent rainy season and repeat after 10 days, if the humid weather persists. Powdery mildew - Erysiphe cichoracearum Symptoms The disease produces white powdery growth on the leavesWhite to grey mildew on the upper surface of older leaves. As plant matures black pin head sized are visible in white mildew areas. The affected leaves more luster, curl, become chlorotic and die.  Symptoms Favorable Conditions The disease is more under dry condition to the end of the winter months. Management Complete field and crop sanitation. Early varieties should be preferred. Removal of infected plant debris. Application of karathane or calixin 1L/ha or wettable sulphur 2 kg/ha is found effective in reducing the disease incidences. Basal rot - Sclerotium rolfsii Symptoms Initial symptoms of the disease appear 40 days sowing. The infected plants can be identified by their sickly appearance. Plants dry up due to the disease infestation. The lower portion of stem is covered with white or brownish white fungal colonies. In extreme cases the plants wilts and dies. Dark brown lesions appear on the base of the stem near ground level, leading to withering. Large numbers of sclerotia are seen.  Symptoms Favourable Conditions Infection occurs in the crop in the month of July and August. The fungus survives through sclerotina in soil and plant debris. Management Deep summer ploughing. Complete field and crop sanitation. Use of resistant or tolerant varieties. Collect and destroy plant debris. Apply Trichoderma on seed and soil to reduce wilt. Apply and incorporate fungus Coniothyrium minitans before sowing as it invades and destroy the pathogen in the soil. Seed treatment with Pseudomonas fluorescens or P.putida strains protect sunflower from Sclerotinia infection during seedling stage. Seed treatment with captan or thiram at the rate of 3 g/kg of seed. Drenching the base of the plant with chestnut compound 3 g per litre of water. Seed treatment with carbendazim at 0.2% followed by the addition of Trichoderma harzianum 10 g/kg soil and spraying Carbendazim at 0.2 % to 15 days old seedling. Necrosis -Tobacco streak virus (TSV) Symptoms  Characterised by the sudden necrosis of part of lamina followed by twisting of leaves and systemic mosaic. Necrosis of lamina of the lamina, petiole, stem floral calyx and corolla. Black streak on stem Necrosis of stems and petioles, terminal growth curls down and plants often lodge Advanced symptoms lead to plant death. Pathogen Caused by Tobacco streak virus an Ilarvirus 25-28 nm, tripartite genome encapzidated separately Disease cycle Virus spreads through transmission by thrips Frankliniella schultzii. Weed hosts serve as natural virus reservoirs. Long and continuous dry spell increases the disease incidence. Management Removal of weed hosts Management of veetor population` Changing planting dates  NORTHERN MARCH 2017 SAFFLOWER SECTION 9 DISEASES ALTERNARIA BLIGHT (CAUSED BY ALTERNARIA CARTHAMI) | PHYTOPHTHORA ROOT ROT (CAUSED BY PHYTOPHTHORA CRYPTOGEA) | RUST (CAUSED BY PUCCINIA CARTHAMI) | OTHER DISEASES  NORTHERN March 2017 Section 9 safflowers Diseases Several diseases can infect safflower, especially in warm and humid conditions. No fungicides are registered for disease control in safflower in Australia; however, some success has been achieved with seed- and foliar-applied products in other countries, including the United States. Control of safflower diseases in Australia relies mainly on using appropriate crop rotations, selecting resistant varieties, using clean seed, controlling volunteer and weed hosts, using sound irrigation practices and selecting appropriate soils. Many safflower diseases are hosted on stubble, volunteer plants, other Carthamus species (e.g. saffron thistle) and some broadleaf crops. The main diseases of safflower in Australia are described below. 9.1 Alternaria blight (caused by Alternaria carthami) Alternaria leaf blight (Figure 1) is the most serious disease of safflower, with heavy infection reducing yield by ≥50%. Infected seed is often smaller with reduced oil content. Figure 1: Alternaria blight infection on safflower leaves. Photo: Hans Henning Mündel 9.1.1 Varietal resistance or tolerance The cultivar Sironaria was bred by CSIRO in 1987 with resistance to Alternaria blight. 9.1.2 Damage caused by the disease Alternaria blight is a fungal disease that attacks leaves, stems, heads and seeds. Transmission may be on infected seed or airborne spores released from crop residue for up to 2 years. 1 9.1.3 Symptoms Infected seeds may have typical sunken lesions on the seedcoat, but they can also appear healthy. Seedborne infection results in reduced germination, death of plants at pre-emergence stage and death or malformation of seedlings. Initial symptoms in established plants often appear as large, brown, irregular spots (lesions) on the lower 1 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy Diseases 1  NORTHERN March 2017 Section 9 safflowers leaves. With warm and humid conditions, the disease then spreads up the plant to infect the upper leaves, stems, flower head, and eventually the seeds. 2 9.1.4 Conditions favouring development Rainfall and high temperatures, or humidity during and after flowering, are the conditions most favoured by Alternaria blight. It can occur in all safflower-growing regions, but it is often more prevalent in northern regions because temperatures in late spring are often warmer and the chance of summer rainfall is higher. Losses can be minimised by avoiding poorly drained soils and by using sound irrigation practices that minimise the incidence of waterlogging. 3 9.1.5 Management of the disease Control of Alternaria blight is largely preventative via careful crop rotation, stubble management and control of volunteer hosts. Sowing at the correct time is also important to minimise the chance of warm, humid conditions after flowering. Seed from infected crops should not be used as planting seed, and resistant cultivars such as Sironaria are available. 4 9.2 Phytophthora root rot (caused by Phytophthora cryptogea) Phytophthora root rot (Figure 2) can be an unpredictable fungal disease and it usually occurs in wet soils, especially when temperatures are high. It is present in all growing areas, but is most prevalent in irrigated crops, where yield may be significantly reduced depending on the timing and extent of infection. Losses tend to be most serious as crops approach maturity. Spread is by spores, which can be transported by wind, rain splash, surface drainage and waterways. Figure 2: Patches of dead plants due to Phytophthora root rot. Photo: Bob Colton 9.2.1 Varietal resistance or tolerance The cultivar Sirothora was bred by CSIRO in 1987 with resistance to Phytophthora root rot. 2 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 3 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 4 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy Diseases 2  NORTHERN March 2017 Section 9 safflowers 9.2.2 Symptoms This disease can infect seedlings, but more often plants are not affected until flowering. Phytophthora root rot usually becomes evident 4–5 days after rain or irrigation. Plants may dry out, appear bleached and collapse in a short time. Lower stems and roots are often discoloured and become rotted. As the plants die, they take on a bleached appearance and the base of the stem and the roots become completely dark. Plants may die individually or in patches that often coincide with low-lying or poorly drained areas where surface water has accumulated around the plants. 5 9.2.3 Conditions favouring development The disease is favoured by wet, warm soil temperatures >25°C. Plants in low-lying areas of paddocks are most susceptible. Phytophthora cryptogea is hosted on a wide range of crops, harboured in the soil and has the ability to survive for long periods in the absence of preferred hosts. Phytophthora cryptogea can infect the fine roots of mayweeds without causing obvious symptoms. 6 9.2.4 Management of the disease i MORE INFORMATION Once infected, plants usually die. Losses can be minimised by avoiding poorly drained soils and by using sound irrigation practices that minimise the incidence of waterlogging. The risk of this disease is one of the reasons that many advisers Sunflower disease management. recommend safflower not be irrigated after flowering. Losses can also be minimised by controlling weeds during fallow to reduce the amount of inoculum present and by growing resistant varieties, especially where crops are irrigated. 7 9.3 Rust (caused by Puccinia carthami) Safflower rust (Figure 3) is often seen on older leaves late in the season, but significant yield losses usually require warm and humid conditions earlier in the growing season. The fungus is borne on seed or soil, and spores from infected plants or crop residues are the main method of spread both within and between crops. Spores can survive on infected stubble from one season to the next and can be spread long distances by wind. 8 Figure 3: Rust pustules on a safflower leaf. 5 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 6 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 7 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 8 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy Diseases 3  NORTHERN March 2017 Section 9 safflowers Photo: Bob Colton 9.3.1 Symptoms i MORE INFORMATION Rust pustules can appear at the base of seedlings, which can collapse and die. In mature plants, rust first appears on the upper leaf surface as small yellow pustules, and on the lower leaf surface or stems at ground level as white pustules. As the Sources of Alternaria carthami disease progresses, the pustules enlarge to form reddish brown pustules up to 3 inoculum in safflower mm in diameter, which may be bordered by a yellow rim. The spores feel like talcum powder when rubbed between the fingers. Severe infection results in premature Phytophthora drechsleri Tucker leaf drop. 9 and Pythium spp. as pathogens of safflower in NSW 9.3.2 Conditions favouring development As with most fungal diseases, safflower rust favours warm, humid conditions where Environmental factors influencing cycles of spore development may occur every 10–14 days. 10 safflower screening for resistance to Phytophthora cryptogea 9.3.3 Management of the disease The main ways to manage rust in Australia are sound crop rotations, control of Survival of Alternaria carthami on volunteer safflower plants and use of clean seed. 11 safflower residue 9.4 Other diseases Fungi associated with root rot of Other, less prevalent diseases of safflower include seedling damping off, grey mould, irrigated safflower in the Namoi charcoal rot, leaf spot and Sclerotinia head rot. Most are favoured by warm, humid Valley, NSW conditions or waterlogging and can be managed by paddock selection, sound crop rotations and use of clean seed. Further advice on managing diseases in safflower can be obtained from plant pathologists or your local agronomic adviser. 12 9 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 10 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 11 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy 12 N Wachsmann, T Potter, R Byrne, S Knights (2010) Raising the bar with better safflower agronomy. Agronomic information and safflower case studies. GRDC, http://www.grdc.com.au/BetterSafflowerAgronomy Diseases 4  10. Diseases of Castor Seedling blight - Phytophthora parasitica Symptoms The disease appears circular, dull green patch on both the surface of the cotyledon leaves. It later spreads and causes rotting. The infection moves to stem and causes withering and death of seedling. In mature plants, the infection initially appears on the young leaves and spreads to petiole and stem causing black discoloration and severe defoliation. Dead seedling Spot on older leaf Leaf blight symptom Pathogen The pathogen produces non-septate and hyaline mycelium. Sporangiophores emerge through the stomata on the lower surface singly or in groups. They are unbranched and bear single celled, hyaline, round or oval sporangia at the tip singly. The sporangia germinate to produce abundant zoospores. The fungus also produces oospores and chlamydospores in adverse seasons. Favourable Conditions  Continuous rainy weather. Low temperature (20-25˚C). Low lying and ill drained soils. Disease cycle The pathogen remains in the soil as chlamydospores and oospores which act as primary source of infection. The fungus also survives on other hosts like potato, tomato, brinjal, sesamum etc. The secondary spread takes place through wind borne sporangia. Management Remove and destroy infected plant residues. Avoid low-lying and ill drained fields for sowing. Treat the seeds with thiram or captan at 4g/kg. Rust – Melampsora ricini Symptoms Minute, orange-yellow coloured, raised pustules appear with powdery masses on the lower surface of the leaves and the corresponding areas on the upper surface of the leaves are yellow. Often the pustules are grouped in concentric rings and coalesce together to for drying of leaves. Powdery mass covering entire leaf Pathogen The pathogen produces only uredosori in castor plants and other stages of the life cycle are unknown. Uredospores are two kinds, one is thick walled and other is thin walled. They are elliptical to round, orange-yellow coloured and finely warty. Disease cycle The fungus survives in the self sown castor crops in the off season. It can also survive on other species of Ricinus. The fungus also attacks Euphorbia obtusifolia, E.geniculata and E.marginata. The infection spreads through airborne uredospores. Management Rogue out the self-sown castor crops and other weed hosts. Spray Mancozeb at 2kg/ha or Propioconazole 1l/ha. Leaf blight- Alternaria ricini Symptoms All the aerial parts of plants viz., leaves, stem, inflorescences and capsules are liable to be attacked by the pathogen. Irregular brown spots with concentric rings form initially on the leaves and covered with fungal growth. When the spots coaleasce to form big patches, premature defoliation occurs. The stems, inflorescences and capsules are also show dark brown lesions with concentric rings. On the capsules, initially brown sunken spots appear, enlarge rapidly and cover the whole pod. The capsules crack and seeds are also get infected. Alterneria leaf spot with concentric rings Pathogen The pathogen produces erect or slightly curved, light grey to brown conidiophores, which are occasionally in groups. Conidia are produced in long chains. Conidia are obclavate, light olive in colour with 5-16 cells having transverse and longitudinal septa with a beak at the tip. Favourable Conditions High atmospheric humidity (85-90 %). Low temperature (16-20˚C) Disease cycle The pathogen survives on hosts like Jatropha pandurifolia and Bridelia hamiltoniana. The pathogen is externally and internally seed-borne and causes primary infection. The secondary infection is through air-borne conidia. Management Treat the seeds with captan or thiram at 2g/kg. Remove the reservoir hosts periodically. Spray mancozeb at 2kg/ha. Brown leaf spot - Cercospora ricinella Symptoms The disease appears as minute brown specks surrounded by a pale green halo. The spots enlarge to greyish white centre portion with deep brown margin. The spots may be 2-4 mm in diameter and when several spots coalesce, large brown patches appear but restricted by veins. Infected tissues often drop off leaving shot-hole symptoms. In severe infections, the older leaves may be blighted and withered. Spots on leaf Pathogen The pathogen hyphae collect beneath the epidermis and form a hymenial layer. Clusters of conidiophores emerge through stomata or epidermis. They are septate and un branched with deep brown base and light brown tip. The conidia are elongated, colourless, straight or slightly curved, truncate at the base and narrow at the tip with 2-7 septa. Disease cycle The pathogen remains as dormant mycelium in the plant debris. The disease mainly spreads through wind borne conidia. Management  Spraying with 1% Bordeaux mixture or Copper oxy chloride @ 0.2% may help to bring the disease under check; but where the cultures of Eri-silk worm are maintained on castor plants, spraying would not be desirable. Use of resistant varieties would be the most effective method for combating the disease. Spraying twice with Mancozeb 2g/lit or Carbendazim 500g/ha at 10-15 day interval reduces the disease incidence. Treat the seed with thiram or Captan 2gm/kg seed. Powdery mildew - Leveillula taurica Symptoms It is characterized by typical mildew growth which is generally confined to the under- surface of the leaf. When the infection is severe the upper-surface is also covered by the whitish growth of the fungus. Light green patches, corresponding to the diseased areas on the under surface, are visible on the upper side especially when the leaves are held against light. Powdery mass covering entire leaf Management When weather is comparatively dry spray twice with wettable Sulphur 2g/lit at 15 days interval, starting from 3 months after sowing. Spray 1ml hexaconazole or 2ml dinocap / litre of water at fortnight intervals. The variety Jwala is resistant to this disease. Stem rot - Macrophomina phaseolina Symptoms Small brown depressed lesions on and around nodes. Increase in size on both directions causing 2 to 20 cm necrotic area. Lesions often coalesce and girdle the stem causing leaf drop. Drying and death starts from apex and progress. Infected capsules discoloured and drop easily. Sudden wilting of plants in patches under high moisture stress coupled with high soil temperature. Plant exhibit symptoms of drought and drooping of leaves. At ground level black lesions are formed on the stem. Young leaves curl inwards with black margins and drop off later, such branches Die-back. Entire branch and top of the plant withers. Affected plant showing drooping of leaves Management Grow tolerant and resistant varieties like Jyothi, Jwala, GCH-4, DCH-30 and SHB-145. Avoid water logging. Destruction of crop debris. Selection of healthy seed. Providing irrigation at critical stages of the crop. Treat the seed with thiram @ 2g/kg or carbendazim at 2g/ kg seed. Seed treatment with Trichoderma viride formulation at 4g/kg of seed. Soil drenching with Carbendazim (1g/1 litre of water) 2-3 times at 15 days interval. Bacterial leaf spot - Xanthomonas campestris pv. ricinicola Symptoms The pathogen attacks cotyledons, leaves and veins and produces few to numerous small round, water-soaked spots which later become angular and dark brown to jet black in color. The spots are generally aggregated towards the tip. At a later stage the spots become irregular in shape particularly when they coalesce and areas around such spots turn pale-brown and brittle. Bacterial ooze is observed on both the sides of the leaf which is in the form of small shining beads or fine scales.  Pustules on lower leaf surface Management Field sanitation help in minimizing the yield loss as pathogen survives on seed and plant debris. Hot water treatment of seed at 58˚C to 60˚C for ten minutes. Grow tolerant varieties. Spray Copper oxychloride 2kg/ha or Streptocycline 100g/ha or Paushamycin 250g/ha. Wilt - Fusarium oxysporum Symptoms When seedlings are attacked cotyledonary leaves turn to dull green colour, wither and die subsequently. Leaves are droop and drop off leaving behind only top leaves. Diseased plants are sickly in appearance. Wilting of plants, root degeneration, collar rot, drooping of leaves and necrosis of affected tissue and finally leading to death of plants. Necrosis of leaves starts from margins spreading to interveinal areas and finally to the whole leaf. Spilt open stem shows brownish discolouration and white cottony growth of mycelia much prominently in the pith of the stem.  Symptoms Management Selection of disease free seeds. Grow tolerant and resistant varieties like Jyothi, Jwala, GCH-4 DCH-30 and SHB 145. Avoid water logging Burning of crop debris Green manuring and intercropping with red gram Treat the seeds with thiram @ 2g/ kg or carbendiazim @ 2g/ kg seed. Seed treatment with 4g of Trichoderma viride talc formulation. Multiplication of 2kg of T.viride formulation by mixing in 50kg farm yard manure Sprinkling water and covering with polythene sheet for 15days and then applying between rows of the crops is helpful in reducing the incidence.