ROOT VEGETABLES - VIRUSES

POWDERY MILDEW
Causal organism: Erysiphe heraclei (syn. E. umbelliferarum)
Description: The fungus creates dense external mycelium with cylindrical conidia on conidiophores. The kleistothecia are formed in clumps, measured by 90-115 μm. The appendixes of kleistothecia are 1-2 times longer than kleistothecium average, simply, brown andnot branching.
Host range: Carrot, celery, parsnip, fennel, dill and umbelliferae weeds.
Occurrence and importance: Powdery mildew is common on root vegetables and is economically non-significant. As it mainly occurs during dry and warm conditions, it is expected to increase in importance as climate change is expected to result in extended dry periods in many regions of Central Europe. Severe infection results in yield reduction (by up to 40%) and poor seed quality. It can be found on autumn-planted carrots and overwinters on the carrot seed crop. It can cause sudden collapse of the plant/crop.
Symptoms:
Image
19. Figure: Erysiphe heraclei
Image
20. Figure: Erysiphe heraclei

Source: Gerald Holmes

The disease affects foliage, stems, and umbels. Patches of white feltlike fungus appear on lower leaves first, then spread to the terminal growth. Young leaves develop small, circular, white, powdery spots that slowly enlarge to cover the leaflets. A slight chlorosis or yellowing may appear on leaves infected by the fungus. The pathogen often covers entire leaves with its masses of white mycelium and powdery spores. Infected foliage becomes brittle and may eventually turn brown, shrivel, and die. Diseased pedicels may turn brown, resulting in the florets' premature death.
Disease cycle: The pathogen survives on overwintered carrots and related weed hosts. The airborne spores may be carried great distances. Foliage symptoms usually do not appear until leaves are mature, and leaves can survive even with heavy infections. Fungal infection and disease development is favoured by high humidity during evening and morning hours.
Control: Use tolerant cultivars and maintain good plant vigour. Isolate new carrot fields from established infected fields. Fungicide application is economically viable only in conditions of periodical disease damage. Sulphur is applicable as prevention.

SCLEROTONIA ROT

Causal organism: Sclerotinia sclerotiorum
Description: Fungus creates white mycelium on infected tissues, with black sclerotia producing mycelia or apothecia. These fungal masses release microscopic ascospores, causing foliar disease when in contact with damaged or senescent carrot or parsley leaves.
Host range: Root and leaf vegetables, rape, sunflower, cucumber and many others (278 genera and 408 species).
Occurrence and importance: Sclerotinia sclerotiorum is one of the most important and widely spread plant pathogens. The fungus is the most destructive disease of carrots. Plants can be attacked during the growing period but most commonly it causes storage rot. The fungus infects the plant in the soil, and symptom-free stored plants can develop sclerotium during humid storage, which can then infect the soil. Crop rotation is suggested. Since Sclerotinia is a polyphagus pest soil disinfection with antagonistic fungi can minimize infections.

Symptoms:

 

Image
21. Figure: Sclerotinia sclerotiorum
Image
22. Figure: Sclerotinia sclerotiorum
Image
23. Figure: Sclerotinia sclerotiorum
Sclerotonia. sclerotiorum infection can occur at any stage of growth, causing root decay and wilt and collapse. The fungus infects the crown and develops as a storage rot. Infected roots appear darker than normal and develop a soft, watery rot in the field or in storage. The disease can spread rapidly on contact between roots. Sclerotinia soft rot differs from Rhizoctonia rot which is firm and dry. Bacterial soft rot is slimy and malodorous and is often secondary to Sclerotinia and other fungal rots.
Disease cycle: Sclerotinia are persistent formula that serve as resting bodies in soil. They germinate after wet weather or irrigation, producing apothecia and ascospores. Infection occurs through leaf tissue near or in contact with sclerotia, and moist soils are necessary for fungal activity.
Control: A 3-year rotation to cereals, corn, or other non-hosts crops may assist the reduction of soil sclerotial populations. Other cultural practises that can decrease incidence of the disease are: deep ploughing, flooding, irrigation management, eliminating of weed hosts, adequate potassium supply and reduction of excess nitrogen. A dense foliar canopy with no gaps results in high humidity above the soil and prolonged periods of leaf wetness within the canopy, creating the ideal environment for infection. These conditions can be avoided by creating adequate air spaces around the foliage. Trimming the sides of the foliage after the canopy closes may increase ventilation between rows and allow leaves to dry. Some variation between cultivars has been reported , but at present dominant resistance is inadequate. Coniotirium diplodiella as an antagonist fungus can be applied in organic agriculture. Prompt postharvest cooling and storage maintenance at 0°C suppresses decay. Fungicide dips can offer additional benefits, but approved registered fungicides are limited. For storage, a controlled atmosphere (controlled air temperature and ventilation) is useful to minimise disease advancement. Stored roots should be checked regularly with any rotting roots being removed and burnt before contamination of the storage area occurs.

 

BOTRYTIS BLIGHT
Causal organism: Botryotinia fuckeliana (anamorph - Botrytis cinerea)
Description: On the surface of colonised tissues, the fungus produces grey mycelium and masses of microscopic conidia (asexual spores) in tiny grape-like clusters. They are hyaline or pale brown.
Botrytis cinerea also produce sclerotia, which are formed on colonised tissue or on mycelium. They are black, compact, measuring 1-15 mm in diameter. The sclerotia generally produce conidia, and occasionally infection hyphae, which can penetrate directly. The sclerotia can also produce apothecia (a sexual fruiting body), which in turn, produce ascospores that are also infective.
Host range: Grey mould rot causes considerable damage on stored carrots, parsnips, mangel, beet, endive, chicory, turnips, etc. In the field, the fungus can infect root and leaf vegetables, sunflower, rape, eggplant, pepper and many other fruits.
Occurrence and importance: Botrytis blight is a significant pathogen affecting vegetable and fruit crops, causing blossom blights, fruit rot, damping-off, bud rot, stem cankers, leaf spots, bulb rots, and root rots. It is problematic in cold storage and shipment, targeting tender tissues, weakened or injured and ageing or dead tissues.
Symptoms:
Image
24. Figure Botryotinia fuckeliana
Image
25. Figure Botryotinia fuckeliana
Image
26. Figure Botryotinia fuckeliana

Source: Kyeong-Hun Park, 2011. CC BY-NC 4.0

Botrytis causes discoloration, water soaking, and a fuzzy grey to tan mould on affected areas, known as RV12-Botrytis blight. Seedlings collapse due to water-soaked stem rot, and grey mould develops on decayed tissue. Damping-off occurs in cold frames and fields, while roots of carrot or parsley can be infected by conidia entering cracks, cuts, or insect wounds.
Disease cycle:  Botrytis cinerea is a fungus that overwinters in soil as mycelium on plant debris or as black, hard, flat, or irregular sclerotia. It can spread in soil and requires free moisture and wet surfaces for germination. It is common in greenhouse-grown crops, especially in spring and autumn when ventilation vents are closed at night. Harvested roots carry the infection in leaf debris, and the fungus can spread into adjacent roots by contact or air-borne spores. Botrytis is important pathogen of vegetables stored at temperatures ranging from 0 to 10°C. Conidia are carried by humid air currents, splashing water, tools, and clothing to healthy plants, where they initiate new infections.
Control: Botrytis blight can be minimized by avoiding overhead irrigation, watering in the morning, and proper plant spacing. Control measures include using high-quality seeds, avoiding heavy soils, overcrowding, and fertilizing plants. Maintaining a dry greenhouse and seedbed soil, maximizing air circulation, and practicing surface watering are essential. Harvesting and handling vegetables should be done in a cool environment with high humidity and close to freezing temperatures. After harvest, collect, remove, and dispose of crop debris. Approved fungicides for foliar application are rare or do not exist in many countries.

 

VIOLET ROOT ROT

Causal organism: Helicobasidium purpureum (anamorph: Rhizoctonia violacea)
Description: Fungus Helicobasidium purpureum forms sterile violet-colored septated mycelium in soil or infected plant tissues, rarely appearing in spring, with long, club-shaped basidiospores.
Host range: Rhizoctonia violacea can attack carrot, celery, parsley, beet, potato, sunflower and many other vegetables and field crops.
Occurrence and importance: Rhizoctonia violacea is an important pathogen of root vegetables, causing rotting in the field and in storage. The disease usually appears in midsummer in patches in the field, often as areas where the carrot or parsley tops are dying, in Central European and Mediterranean countries.

Symptoms:

Image
27. Figure Helicobasidium purpureum

Source: https://www.leicesters.co.nz/

Image
28. Figure: Helicobasidium purpureum

Source: https://www.leicesters.co.nz/

Early symptoms of carrot and parsley root infections are horizontal dark brown lesions occurring during wet periods. These lesions form large, deep, rotten areas in mature plants with thick mycelial wefts and spores. Small initial lesions enlarge and coalesce, forming dark purplish-brown, firm, leathery decay. The disease agent penetrates deeper into root tissues during storage, and diseased carrots often have a significant soil adhering mass.
Disease cycle: Helicobasidium purpureum persists in the soil as saprophyte on plant debris. Disease development requiress high soil moisture, heavy soil, high nitrogen fertilisation. n the storage, the relative high humidity and higher temperatures is favourable for the disease.
Control: Control of this disease is nearly impossible if late summer and fall conditions are wet. Earlier harvests, planting on ridges, crop rotation, careful handling during harvest, storage sanitation and extremely good storage conditions might reduce losses to the disease. Reducing the spread of infected soil on cultivation and harvesting equipment is also important.


 

BLACK ROT

Causal organism: Stemphylium radicinum
Description: The fungal mycelium is grey to blue-black, well branched and septate Conidiophores are like hyphae, little dark, appeared as lateral branches. On their ends, the conidia are formed singly or in clusters. The conidia are ellipsoid, round in both ends, pale brown to dark brown with age, with 2-3 longitudal septate. The conidia are 34-51 µm long and 10-22 µm wide.
Host range: Carrot, celery, parsley, parsnip and fennel.
Occurrence and importance: Black rot is widely distributed throughout the world. It attacks any part of plants and belongs to the most important storage diseases of root vegetables. The field and storage damage depend on cultural practices and storage conditions, and losses may be >60%.  Black rot is a pest which has been present for a long time, but can cause field infections which can result in huge damage before harvest. The fungus remains infectious for several years, in many cases attacking young plants. The protective measures required is differ from violet root rot.
Symptoms:
Image
29. Figure: Stemphylium radicinum

Source: www.koppert.com

Stemphylium radicinum causes damping-off in the field, causing infected foliage to turn black and die. Root infections appear as tiny, black spots, and the taproot may develop multiple growing points. In stored carrots, the spots are round, shallow, and slightly depressed. Root tip rot may be caused black rot, which occurs on the crown and core.
Disease cycle: Stemphylium radicinum survives on plant debris in the soil, but infested seed is probably the most important source of infection. In root vegetable storage, infected storage rooms can cause infections. The disease agent requires a relative humidity above 92% and 28°C for rapid development, but decay can progress even at 0.5°C.
Control: Cultural practices including correct crop rotation, using seed treated with hot water or fungicide, cleaning and disinfecting storage houses, maintaining a low temperature and humidity, and using chemical treatments for seed crops. Trichoderma species can be used as antagonists.
 

CERCOSPORA LEAF BLIGHT

 

Causal organism: Cercospora carotae
Description: Cercospora carotae causes leaf spots, causing curling and blight on leaves. These small, circular, tan or grey to brown spots develop a chlorotic halo, leading to leaflet withering and death. The fungus attacks younger leaves and plants, but can also cause lesions on petioles and stems, causing leaves to die.
Host range: Carrot.
Occurrence and importance: Cercospora leaf blight is a widespread root vegetable disease, developing rapidly in hot or humid weather, typically occurring in July and early August. It is less important than other diseases like Alternaria or Sclerotinia, but can cause severe foliage loss. Cercospora emerges sooner under irrigation and requires new control methods. Can cause significant economic damage due to yield reduction in leafy crops.
Symptoms: Leaf spots caused by Cercospora carotae first appear along the margins of the leaves, often causing the leaves to curl. However, symptoms are usually most severe and obvious along leaflet margins. Spots inside the leaf edges are small, roughly circular, and tan or grey to brown with a dead centre (RV17-Cercospora leaf blight). A chlorotic halo often develops around these spots. As the lesions increase in number and size, the entire leaflet withers and dies. The fungus attacks younger leaves and plants in preference to older ones. In heavily infested fields, however, both older and younger leaves are subject to attack. The pathogen also produces lesions on the petioles and stems, characterised by dark brown borders and tan to grey centres. The lesions may merge and girdle the stems, causing the leaves to die.
Image
30. Figure: Cercospora carotae

Source: www.agic.wa.au

Image
31. Figure: Cercospora carotea

Source: www.growveg.co.uk

Disease cycle: Cercospora overwinters in the soil in crop residues and produces several cycles of infection during each growing season, depending upon weather conditions. Cercospora carotae can be seedborne, but also survives between crops on plant debris or in the soil. Infection occurs in connection with high temperatures and moist weather.
Control: Control disease by removing crop refuse, practicing crop rotations, using resistant cultivars, and using fungicides for root vegetable production.

 

PYTHIUM LEAF BLIGHT

Causal Agent and Hosts: Pythium
Description: Sugar beet root rot can be caused by seed-borne fungi. These are Phoma betae, Fusarium spp., Alternaria tenuis. It can also be caused by soil-borne fungi such as Pythium spp., Aphanomyces spp., Fusarium spp. and Rhizoctonia solani. Their prevalence in soils in the study area is 10-90%, generally requiring reseeding of 5-10% of the area. Yields are reduced by 25-40%. The uneven stand causes healthy beets to overgrow, their sugar content decreases and they are damaged at harvest. Harvest losses in such stands can be as high as 25-40%.
Disease cycle: Seed-borne pathogens reduce beet germination by 10-15% in warm, rainy weather, multiply on the surface, and damage the germ. Soil-dwelling pathogen abundance depends on humus content and pre-sowing conditions, facilitating outbreaks and causing severe damage in prolonged emergence.
https://agro.bayer.co.hu/termekek/karositok/korokozok/?id=95
Control: using hyperparasitic fungi A hyperparasitic fungal species, Pythium oligandrum, is used to treat fungi causing damage to plants and cell wall degradation. This treatment stimulates plant tissue defence processes that inhibit pathogenic microorganism growth. This treatment is effective against a wide range of pathogens including Alternaria, Botrytis cinerea, Fusarium, agabaenophyte ergot, phytophthora root rot, white mould, and Verticillium wilt, in various crops, is compatible with organic farming and ideally combined with preventive treatments.
Ref.: https://www.kite.hu/tudastar/polyversum-gombaval-a-gombak-ellen/286)

 

CARROT ALTERNARIA LEAF BLIGHT

Causal organism: Alternaria dauci (syn. Alternaria porri f. sp. dauci)
Host range: Alternaria dauci can infect carrot, parsley and fennel.
Occurrence and importance: In conditions favouring disease development, the lesions will join together causing the leaflets to shrivel and die though burnt. Rainy leaf blight is most severe later in the season on older tissue, usually in late August and September. The diseases can be easily confused with herbicide injury to carrot leaves.

Image
32. Figure: Alternaria dauci

Source: www.Plantpath.ifas.ufl.edu

Symptoms: Alternaria leaf blight affects carrot leaves, causing dark brown to black irregularly shaped lesions on leaf blades and petioles. Spots on older leaves can kill entire leaves, and weakened leaves may break off when gripped by mechanical harvesters. The pathogen also causes damping-off of seedlings and root decay. Root lesions are irregular, dark brown to black, appearing as a shallow, firm area of decay. It makes mechanical harvesting difficult.

Image
33. Figure: Alternaria dauci - Necrotic lesions caused by Alternaria dauci on carrot leaves.

Source: ag.perdue.edu

Disease cycle: Alternaria blight is a fungal disease that spreads rapidly on older leaves of a maturing crop due to poor air circulation and dense foliage. Infected leaves produce spores that infect younger leaves and attack roots. Alternaria survives on seed and overwinters on crop residues, wild plants, and seeds. It thrives in cool, humid weather.
Control: To control disease, follow cultural practices like planting Alternaria-indexed seeds, turning under carrot residues, practicing good crop rotations, and not planting near blight-stricken fields. Use seed treatments like thiram-Pomarsol Forte to reduce A. dauci.
 

Listo of Viruses:

  • IRIS YELLOW SPOT VIRUS [IYSV]

For more information on viruses, follow this link.

Listo of bacterial:
  • BACTERIAL SOFT ROT
  • BACTERIAL BROWN ROT
  • BACTERIAL RING ROT
For more information on the bacterium, follow this link.
Listo of fungi:
  • POWDERY MILDEW
  • SCLEROTONIA ROT
  • BOTRYTIS BLIGHT
  • VIOLET ROOT ROT
  • BLACK ROT
  • CERCOSPORA LEAF BLIGHT
  • PYTHIUM LEAF BLIGHT
  • CARROT ALTERNARIA LEAF BLIGHT 29
For more information on fungi, follow this link.
List of insects:
  • EUROPEAN MOLE CRICKETS
  • CLICK BEETLES, WIREWORMS
  • POTATO TUBER MOTH (TUBERWORM)
  • TURNIP MOTH
  • SPIDER MITES
  • THRIPS
  • CARROT FLY
  • APHIDS
For more information on insects, follow this link.
© 2024 INPACT project .