Soya bean crop diseases A Lecture by Mr Allah Dad Khan

Soya bean crop diseases A Lecture by Mr Allah Dad Khan

1. Soyabean Crop Diseases A Presentation To IPM Course/FFS Participants By Mr. Allah Dad Khan Provincial Coordinator IPM KPK For MINFAL Pakistan

2. Symptoms: Phytophthora  can attack and rot seeds prior to emergence, and can cause pre- and post -emergence damping off.Phytophthora rot is a widespread disease.At the primary leaf stage (V1), infected stems appear bruised and are soft, secondary roots are rotted, the leaves turn yellow, and plants frequently wilt and die.A related pathogen,  Pythium , causes similar symptoms and can only be differentiated by laboratory examination. 1.Phytophthora Seed & Seedling Blight

3. Pathogen Involved: Disease Management: Phytophthora sojae  is a fungal-like pathogen that survives in soil for up to 5-10 years in association with decomposed soybean tissues.Soybean is the only known crop host for this pathogen.This pathogen infects soybean at all stages of development, and is most active and causes most damage in wet soils. Resistant varieties. Varieties with race-specific resistance should be used. Varieties that have high levels of tolerance to  Phytophthora  rot may reduce the seedling and adult phase of the disease.Fungicidal seed treatments can also reduce damage to seed and young seedlings.Soil drainage should be improved if possible, and low areas of fields should be avoided, especially if a field has a history of seedling or root rot problems.Crop rotation may be of some benefit. 1.Phytophthora Seed & Seedling Blight

4. Symptoms: Pythium  can attack and rot seeds and seedlings prior to emergence, and can cause post-emergence damping off under wet conditions.The characteristic symptom of most  Pythium  infections is soft, brownish-colored, rotting tissue.In established plants, secondary roots can be soft and rotted and plants may be stunted or killed in some cases. Phytophthora  is a related pathogen that causes similar symptoms and the two can only be differentiated with laboratory examination. 2. Pythium Seedling and Root Rot

5. Pathogen Involved: Disease Management: Pythium  infects at all stages of development, and is active in wet soils. Pythium  is a soilborne , fungal-like pathogen. Several different species of this pathogen damage soybeans.The various species of  Pythium  that infect soybean have a wide host range that can include corn and many other crops. Plant in soils warmer than 55°F.Resistant varieties are not available.Soil drainage should be improved if possible, and low areas of fields should be avoided, especially if a field has a history of seedling or root rot problems.Some seed treatments can reduce seed and seedling rot. Pythium Seedling and Root Rot

6. Symptoms:   Rhizoctonia root rot is a widespread and common seedling and root-rotting disease of soybean.Damage prior to emergence is common but difficult to identify.In seedlings and older plants, a reddish-brown sunken lesion is a characteristic symptom of  Rhizoctonia   infection. Fusarium solani , which causes seedling rot, is commonly associated with  Rhizoctonia  infections. It is not possible to identify dual infections in the field.The infections can be superficial and cause no noticeable damage to plants, or they can girdle the stem and kill or stunt plants.Seedlings or older plants may be stunted and may wilt from a firm, dry, brown to reddish brown decay or sunken lesion on the root and stem below or near the soil line. 3. Rhizoctonia Root Rot

7. Pathogen Involved: Disease Management: Rhizoctonia solani  (a soilborne fungus).It has a wide host range that may include corn, alfalfa, and soybean. Crop rotation and some seed treatments can reduce damping-off and root rot.Tillage may be of value where disease was severe.Encourage seedling health with good agronomic practices and avoid herbicide stress. Rhizoctonia Root Rot

8. Symptoms  Early infections by the fungus can result in pre- and postemergence damping-off. Foliar symptoms appear later in the growing season and include petiole cankers, leaf rolling, necrosis of the laminar veins and premature defoliation. As the plants approach maturity (R7-8), the fungus can produce acervulli (fruiting bodies that resemble black specks) on the stems and pods. These bodies occur randomly on the stems – not in linear rows as with pod and stem blight. If the disease continues to develop on the pods, seed quality will be compromised. 4. Anthracnose Colletotrichum truncatum (fungus)

9. Pathogen Involved: Disease Management: Colletotrichum truncatum ,  Glomerella glycines  and other fungiThese pathogens overwinter in infected crop residue and infected seeds. Soybean varieties differ in their resistance to anthracnose.Plant pathogen-free seed.Treatment of infected seeds with a fungicide is recommended.Fungicidal sprays may be helpful after bloom 4. Anthracnose

10. Symptoms: Can occur on all aerial plant parts, but lesions on leaves and pods are easiest to see.Infections begin as small, water-soaked spots that turn yellow and then brown as the tissue dies.Spots may merge to form dead patches, and the dead tissue may fall out.Seedlings may be stunted or killed if apical tissue is infected, and brown lesions may cover much of infected pods. 5. Bacterial Blight

11. Pathogen Involved: Disease Management: Pseudomonas syringae   pv .  glycinea  (a bacterium), also infects snap bean and lima bean.The pathogen overwinters in crop residue and can be seed transmitted. Plant resistant varieties.Rotate with non-host crops.Use pathogen-free seedAvoid field cultivation when foliage is wet. Bacterial Blight

12. Symptoms: Cercospora blight/purple seed stain is the No. 1 soybean disease in Louisiana. The fungus can infect seedlings, resulting in plant death or latency. Foliar symptoms of this disease usually are not evident until soybeans are in the mid- to late reproductive growth stages. Initial symptoms appear as small, chocolate brown lesions on the petioles near the base of the leaflet. As the disease progresses, foliar symptoms are expressed as a reddish-brown to tan discoloration on the upper leaf surfaces in the upper canopy. Leaves may have a leathery appearance. The fungus can sporulate in older lesions and resemble ashes. Advanced stages of this disease result in premature defoliation, discolored pods and reduced seed quality. The seed phase of this disease is evidenced by purple-stained seeds at harvest. 6. Purple Seed Stain and Cercospora Leaf Blight

13. Pathogen Involved: Disease Management: Cercospora kikuchii  (a fungus).Survives from year to year on infested debris or seed.This fungus overwinters in soybean tissue and in infected seeds.The same pathogen also causes Cercospora blight and leaf spot, which can reduce yields. Use pathogen-free seed.Some varieties are less susceptible than others.Rotation out of soybeans may be helpful.Foliar and seed treatment fungicides may provide some control Purple Seed Stain and Cercospora Leaf Blight

14. Symptoms: The initial symptoms are small light green spots (not water-soaked) with raised, centers on the upper and lower surfaces of leaves.Tan to gray tufts of fungal growth often develop on lower leaf surfaces, especially under wet and humid conditions.It can cause defoliation and reduced yields, but yield losses are typically minimal.The lesions can grow together into large irregular brown areas. Pod and seed infection can also occur. Seeds may become covered with a whitish coating. 7. Downy Mildew Peronospora manshurica (fungus)

15. Pathogen Involved: Peronospora manshurica   (a fungus).Common snap bean is another host.It overwinters on infected leaves and seeds, and can be transmitted by seed. Disease Management: Select resistant soybean varieties.Use appropriate seed treatments.Bury infested residue where feasible and where disease has been severe.Rotate w Downy Mildew Peronospora manshurica (fungus)

16.   Symptoms: All aerial plant parts can be infected, and infected areas typically appear as if white flour has been spread unevenly onto the plant surfaces.Symptoms are easiest to see on leaves, and may vary among cultivars to include yellow patches and defoliation.This disease is sporadic but is a common diseases on soybean plants grown in greenhouses for research. 8. Powdery Mildew

17. Pathogen Involved: Microsphaera diffusa  (a fungus). Other hosts include common bean, pea, and cowpea. Disease Management: Plant resistant varieties.Foliar fungicides may not be economically beneficial. Powdery Mildew

18. Symptoms: Infections begin on lower leaves and develop later on upper leaves.Small dark brown spots (pinpoint to 1/5" in size) called pycnidia develop on both surfaces of leaves, the spots may grow together to create irregular brown patches.Infection begins on the lower leaves and progresses upward.Infected leaves turn brown and yellow and may drop prematurely.Septoria brown spot is a common foliar disease that has been reported to cause insignificant to minor losses 9. Septoria Brown Spot

19. Pathogen Involved: Septoria glycines  (a fungus). It infects many varieties of legumes .This pathogen overwinters on infected plant debris and may be seed transmitted. Disease Management: Rotate with non-legume crops.Resistant varieties are not available.Tillage and fungicides may be warranted under some conditions. Septoria Brown Spot

20. Symptoms: Soybean mosaic causes stunting of plants and crinkled and mottling of leaves.Infected plants range from no symptoms to severely mottled and deformed.The leaf blades are puckered along the veins and curled downward.The mottling appears as light and dark green patches on individual leaves.Symptoms can be difficult to see when temperatures are above 90°F.Do not confuse with growth regulator herbicide damage where the leaves will be elongated and which usually occurs in a pattern such as along a field edge.Soybean mosaic can also reduce seed size and pod number per plant, and soybean mosaic is one of several factors associated with discoloration of seeds, causing a dark discolored tear stain origination at the hilum.The virus can interact with  bean pod mottle virus  ( BPMV ) to create severe symptoms in plants infected with both viruses. 10. Soybean Mosaic  

21. Pathogen Involved: Soybean mosaic virus (SMV). This virus has a wide host range including pea and snap bean.SMV is transmitted by aphids and infected seed. Disease Management: Plant seeds free of SMV.Plant early. Soybean Mosaic  

22.   Symptoms: Symptoms begin on the lower leaves of the plant, usually in the lower plant canopy. Small pustules (gray to tan or brown) surrounded by necrotic areas usually develop first on the underside of leaves on the lower part of the plant. Lesions can also appear on pods and stems. Tiny, raised pustules develop in the lesions, and the pustules break open and release tiny tan to gray spores. 11. Soybean Rust Phakopsora pachyrhizi (fungus)

23. Pathogen Involved: Two species of rust fungi cause soybean rust. Phakopsora pachyrhizi (aggressive Asian pathogen) and P. meibomiae (mild pathogen). Only P. pachyrhizi causes significant yield losses. Both cause the same symptoms, and they can be distinguished only with specialized laboratory tests. These fungi are obligate pathogens that survive only on green, living host plant tissue, and are readily dispersed long distances by wind Disease Management: Scout soybean lower canopy weekly. Soybean rust can be managed with the judicious use of fungicides that must be applied properly and at the correct time. Soybean Rust Phakopsora pachyrhizi (fungus)

24. Symptoms: Symptoms begin on the lower leaves of the plant, usually in the lower plant canopy. Small pustules (gray to tan or brown) surrounded by necrotic areas usually develop first on the underside of leaves on the lower part of the plant. Lesions can also appear on pods and stems. Tiny, raised pustules develop in the lesions, and the pustules break open and release tiny tan to gray spores. 12. Soybean Rust Phakopsora pachyrhizi (fungus)  

25. Pathogen Involved: Two species of rust fungi cause soybean rust. Phakopsora pachyrhizi (aggressive Asian pathogen) and P. meibomiae (mild pathogen). Only P. pachyrhizi causes significant yield losses. Both cause the same symptoms, and they can be distinguished only with specialized laboratory tests. These fungi are obligate pathogens that survive only on green, living host plant tissue, and are readily dispersed long distances by wind. Disease Management: Scout soybean lower canopy weekly. Soybean rust can be managed with the judicious use of fungicides that must be applied properly and at the correct time. Soybean Rust Phakopsora pachyrhizi (fungus)

26.   Symptoms: The key symptoms are browning of the vascular system and often there is brown and yellow discoloration between the leaf veins.If stems are split the stems late in the season, healthy stems have white pith tissue, while infected tissue is dark brown.The browning may only occur at the nodes or lower stem.Leaves may turn brown and dry while remaining attached to the stem, although the leaf symptoms may or may not develop depending on cultivar and environment.The leaf symptoms can be confused with those of  SDS , but the two diseases can be differentiated by internal stem symptoms. 13.Brown Stem Rot (BSR)

27. Pathogen Involved: Phialophora gregata  (a fungus).This pathogen overwinters in soybean stem residue and in soil.Two genotypes are recognized that may cause different symptoms on different soybean varieties.Brown stem rot is widespread in the Midwestern states. It is most common in northern areas. Disease Management: Use resistant soybean varieties.Rotation to non-host crops may be helpful. SCN  may interact with BSR, and resistance to  SCN  may reduce problems with BSR. Brown Stem Rot (BSR)

28. Symptoms can occur throughout the growing season. Infected seed may not germinate, or seedlings may die soon after emergence. Symptoms from plants with latent or mid-to-late-season infections die prematurely during hot, dry weather. Symptoms can be associated with dry spots (sandy areas) in the field. The roots and lower stems are deteriorated, and the epidermal and subepidermal tissue will be silvery and covered with sclerotia (survival structures) that look like black pepper 14. Charcoal Rot Macrophomina phaseolina (fungus)

29. Symptoms Soybeans can be affected during any growth stage. Symptoms associated with this disease include yellowing of the foliage, wilting and a chocolate brown lesion at the base of the stem. There is an immediate transition from the brown lesion to green stem. This lesion can extend several inches above the soil line. In some cases, the plants appear to recover from this disease if growing conditions improve. 15. Phytophthora Rot Phytophthora spp. (fungus)

30. Pathogen Involved: Phytophthora sojae  is a fungal-like pathogen that survives in soil for up to 5-10 years in association with decomposed soybean tissues.Soybean is the only known crop host for this pathogen.This pathogen infects soybean at all stages of development, and is most active and causes most damage in wet soils. Disease Management: Resistant varieties. Varieties with race-specific resistance should be used. Varieties that have high levels of tolerance to  Phytophthora  rot may reduce the seedling and adult phase of the disease.Fungicidal seed treatments can also reduce damage to seed and young seedlings.Soil drainage should be improved if possible, and low areas of fields should be avoided, especially if a field has a history of seedling or root rot problems.Crop rotation may be of some benefit. Phytophthora Rot Phytophthora spp. (fungus)

31.   Symptoms: Initial lesions usually develop at stem nodes during or after flowering.The lesions expand and the tops of the plants initially become grayish-green and then wilt and die.Infected areas often become soft and watery, and become covered with white moldy growth in moist conditions.Hard , black sclerotia develop on or inside infected stems and pods.Occurrence of white mold varies widely from year to year and from location to location. 16. Sclerotinia Stem Rot (White Mold)

32. Pathogen Involved: Sclerotinia   sclerotiorum  (a fungus).Survives from year-to-year in soil or stems in the form of hard black masses of mycelium ( sclerotia ). Sclerotia germinate near the soil surface to form small mushroom-shaped structures called apothecia, which produce ascospores that are spread by wind to infect dead soybean flowers.Seed lots can be contaminated with sclerotia and seeds can be infected with the pathogen.The host range of this pathogen includes many broadleaf plants, but not corn or small grains. Disease Management: Use seed free of  Sclerotinia  contamination and infection.Reduce or avoid irrigation until seed has set.Careful selection of soybean varieties may be helpful because some varieties are more susceptible than others.Foliar fungicides may be beneficial but may not be economically beneficial. Sclerotinia Stem Rot (White Mold

33. Symptoms: SCN infects roots and aboveground symptoms are not always present even though yield loss due to SCN may significant.The disease is best diagnosed by looking for tiny white to yellow lemon-shaped females on the roots beginning toward the end of June and then throughout the rest of the season.The cysts often become brown late in the season. In fields with very high levels of SCN, heavily infected plants may be stunted and yellow or chlorotic, particularly under low fertility or drought conditions.Badly infested areas may be oval to somewhat elliptical in outline.Such areas show the most severe damage in the center with less damage toward the margin 17. Soybean Cyst Nematode (SCN)

34. Pathogen Involved: Heterodera glycines  (a nematode).Host range includes soybean and numerous legume and weed species.Numerous different types of the nematode occur that are pathogenic to different sources of resistance. Disease Management: The first step is to test soil samples to determine if SCN is in a field.Soybeans should be rotated with non-host crops.Resistant soybean varieties should be planted, and different resistant varieties should be rotated.Manage weeds, moisture, and fertility to reduce plant stress Soybean Cyst Nematode (SCN)

35. Symptoms: Initial symptoms are reddish brown, slightly sunken lesions that appear at the base of branches or leaf petioles.These lesions can develop into elongated, sunken, dark brown cankers.Brown discoloration may also occur inside the stem.Plant parts above the lesions may die. Leaves may develop necrosis and chlorosis between the veins, and may remain attached after death.Lesions may be found at the soil line, making it easy to confuse this disease with Phytophthora rot .Stem canker does not cause root rot, while Phythophthora rot causes root rot.Tiny black dots may appear on the stem singly or in clustered groups on plants killed by stem canker. 18. Stem Canker

36. Pathogen Involved: Diaporthe phaseolorum  var.  caulivora , a fungus that causes northern stem canker. Diaporthe phaseolorum  var.  merdionalis , a fungus that causes southern stem canker.These pathogens overwinter in infested soybean residue, and may be spread with infected seed. Disease Management: plant resistant or moderately resistant varietiesdelayed planting may be beneficialfoliar fungicides may be beneficial tillage can reduce disease problems in fields where stem canker has been a problem Stem Canker

37.   Symptoms: The most commonly observed symptoms are on severely affected leaves, but the primary disease is a root rot.Initial symptoms are usually scattered chlorotic spots that occur between the veins on leaves, and the leaves may be cupped or curled.These spots typically enlarge between veins to become brown lesions surrounded by chlorotic areas.As the disease progresses, the leaves detach from the petioles. Roots become rotted and plants may be pulled easily from the ground.Gray discolored areas develop inside the root and in the vascular tissue of the lower stem.The pith remains white, which is a diagnostic feature that distinguishes this disease from brown stem rot 19. Sudden Death Syndrome (SDS)

38. Pathogen Involved: Fusarium solani   f.sp .   glycines  (a fungus).Soybean appears to be the main host of this pathogen, but snap and lima bean may be infected.This pathogen overwinters in soil. Disease Management: Plant soybean varieties with the highest level of tolerance or resistance available.Reduce excessive soil moisture with drainage and minimize compacting.Manage fields to reduce  SCN   populations.Stagger planting dates. Sudden Death Syndrome (SDS)

39.   Symptoms: Initial lesions usually develop at stem nodes during or after flowering.The lesions expand and the tops of the plants initially become grayish-green and then wilt and die.Infected areas often become soft and watery, and become covered with white moldy growth in moist conditions.Hard , black sclerotia develop on or inside infected stems and pods.Occurrence of white mold varies widely from year to year and from location to location. 20. Sclerotinia Stem Rot (White Mold)

40. Pathogen Involved: Sclerotinia   sclerotiorum  (a fungus).Survives from year-to-year in soil or stems in the form of hard black masses of mycelium ( sclerotia ). Sclerotia germinate near the soil surface to form small mushroom-shaped structures called apothecia, which produce ascospores that are spread by wind to infect dead soybean flowers.Seed lots can be contaminated with sclerotia and seeds can be infected with the pathogen.The host range of this pathogen includes many broadleaf plants, but not corn or small grains. Disease Management: Use seed free of  Sclerotinia  contamination and infection.Reduce or avoid irrigation until seed has set.Careful selection of soybean varieties may be helpful because some varieties are more susceptible than others.Foliar fungicides may be beneficial but may not be economically beneficial. Sclerotinia Stem Rot (White Mold)