Management of Carrot Diseases Common Post-Harvest Diseases the ﬁ Eld Before Harvest

VEGEnotes Carrot Diseases CarVY only infects carrots and closely related Black root rot plants e.g. parsnip, coriander and chervil. Two fungi cause black root rot: Thielaviopsis Control basicola (Chalara elegans) and Chalaropsis • Avoid planting sequential side-by-side crops thielavioides. Roots affected by black root and separate crops by planting non-hosts, rot have large black superfi cial patches on them. These patches are often circular and VEGE such as brassicas, between them notes sometimes surrounded by a matt white halo. • Remove volunteer carrots and harvested carrot crops promptly Disease cycle Your levy @ work • Use a fallow period to break the infection The fungi that cause black root rot have a cycle wide host range and occur in soil. Carrots are likely to be contaminated with these fungi in Management of Carrot Diseases Common post-harvest diseases the fi eld before harvest. Bacterial soft rot Common leaf diseases • Use seed that has been treated with After harvest the fungi infect carrots through fungicide This is a soft, slimy, orange rot that can occur wounds or abrasions. Leaf blight • Use fungicide sprays, such as chlorothalonil, on any part of the carrot, although it is often They develop rapidly on Leaf blight is an extremely common, quickly copper, difenoconazole, mancozeb, metiram associated with the eyes. The rot can penetrate carrots stored at 25°C spreading fungal disease that initially occurs and zineb. Start the spraying program when deeply. It does not usually smell unpleasant and in high humidity. as patches within crops. The symptoms of the fi rst sign of blight appears unless there is secondary infection caused by Control leaf blight are small brown, dead spots on the other bacteria. Common root diseases • Losses caused by leaves and petioles (leaf stalks). These spots Soft rot is caused by black root rot can be grow rapidly and eventually join so that the Sclerotinia or cottony rot leaf yellows and dies. The petioles also break either Erwinia carotovora minimised by rapid Sclerotinia is a common fungal disease that during harvesting. subspecies carotovora or cooling of harvested affects many vegetables. It E. carotovora subspecies carrots and storing There are two types of leaf blight, Alternaria affects carrots both in the atroseptica. them at 0°C and Cercospora. Alternaria leaf blight is fi eld and in storage and Disease cycle • Minimise mechanical Symptoms of black caused by Alternaria dauci and/or A. radicina is caused by the fungus root rot. damage during and usually fi rst appears on the oldest Sclerotinia sclerotiorum. Erwinia spp. are common leaves. Cercospora leaf blight is caused harvesting and in the packing shed In the fi eld, the fi rst soil bacteria that survive on by Cercospora carotae and appears on the symptoms are water- crop residues. Carrots are Sclerotinia rot or cottony rot youngest leaves fi rst. likely to be contaminated soaked spots at the base with soft rot bacteria in See Sclerotinia above. Disease cycle of the petioles and at the fi eld before harvest. Further Information Both Alternaria and Cercospora can be carried the crown. The outer Symptoms of bacterial However, these bacteria on carrot seeds and once introduced into an leaves redden and wilt. soft rot. Dr Elaine Davison are readily spread in area will survive on carrot debris. They can There is often a white, Department of Agriculture Western Australia washing water during post- spread easily during rain or irrigation and can cottony fungal growth ph: (08) 9368 3690 harvest handling. also be carried on machinery. in the surrounding soil. email: [email protected] Eventually the top of the Soft rot bacteria enter carrots through wounds, Control Acknowledgements carrot becomes soft and but they can also be forced into the eyes if warm • Disease control is diffi cult on farms where slimy. carrots are dumped into deep cold water tanks. Dr Elaine Davison carrots are planted sequentially Once the bacteria are in the carrot root they Allan McKay • Some carrot varieties are more tolerant of cannot be killed by sanitisers such as chlorine. Dr Roger Jones Symptoms of sclerotinia. leaf blight than others

Control Disclaimer: The Chief Executive Offi cer of the Department of Agriculture and the State of • Losses caused by soft rot bacteria can be Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it. The Bottom Line minimised by cooling carrots as soon as • Fungal, nematode, viral and bacterial possible after harvest and then storing them DISCLAIMER: Every attempt is made to ensure the accuracy of all diseases can affect carrots at any stage of at 0°C statements and claims made in Vegenotes. However, due to the nature of the crop, from seedlings to cold storage • Minimise mechanical damage during the industry, it is impossible for us to know your precise circumstances. Therefore, we disclaim any responsibility for any action you take as a • Root and post-harvest diseases affect harvesting and in the packing shed result of reading Vegenotes. marketability of carrots, while foliar diseases affect the yield of crops ISSN: 1449 - 1397 Copyright©: Horticulture Australia 2004 Level 1, 50 Carrington Street • For export, growers should ensure that No part of this publication can be copied or reproduced without Sydney NSW 2000 Australia chemical use complies with the maximum the permission of the original authors. Telephone (02) 8295 2300 residue limits of the importing country Symptoms of leaf blight. VEGEnotes is coordinated, edited & printed by: Facsimile (02) 8295 2399 ARRIS Pty Ltd, ph 08 8303 7247 fax 08 8303 6752 www.horticulture.com.au Your levy @ work Spring 2004 VEGEnotes Carrot Diseases If slightly infected carrots are harvested the rot Disease cycle Disease cycle The four species of root lesion nematode continues to develop during storage and can Pythium spp. are soil borne pathogens that Root knot nematodes are diffi cult to control in Australia that infect carrots are: spread to adjacent carrots. persist as resting spores between crops. because they have wide host ranges. They Pratylenchus crenatus, P. neglectus, P. are more usually a problem in sandy soil. penetrans and P. thornei. These carrots then develop a soft, watery, slimy Pythium sulcatum only infects carrots and Root knot nematodes survive between crops rot at the crown. A white cottony fungus develops closely related plants, it can survive for at least Disease cycle on alternate hosts and in egg masses in the from this rot; it often contains small black two years between carrot crops. Pythium Like root knot nematodes, Pratylenchus are soil. sclerotes that look like mouse droppings. violae has a much wider host range and can diffi cult to control because they have wide Disease cycle survive for at least fi ve years between carrot When conditions are suitable, the eggs hatch host ranges, including cereal nurse crops. crops. and juvenile nematodes penetrate root tips. They are a problem in sandy soils and Sclerotinia is a common and widespread soil Female nematodes mature within the roots survive between crops either on alternate Cavity spot caused by Pythium sulcatum is borne pathogen, with a host range that includes and a gall develops around the nematode. hosts or as eggs in the soil. most severe in summer and autumn harvested both commercial crops and weeds. Black, hard These females lay eggs into a gelatinous crops, while cavity spot caused by Pythium When conditions are suitable, the eggs hatch sclerotes form on infected plant debris and these matrix on the root surface. The eggs either violae is most severe in winter harvested and juvenile nematodes penetrate carrot persist in the soil for up to fi ve years. hatch immediately or become dormant. crops. roots. The nematodes migrate and multiply Sclerotes close to the soil surface infect old Control within the roots. leaves and petioles. The infection spreads down Control • Soil sampling to assess the petioles to the crown, resulting in rotting at • Cavity spot control is diffi cult on farms with Control nematode numbers the top of the roots. limited rotation • Sample soil to assess nematode numbers before seeding is before seeding to determine whether a Control • Grow varieties such as Stefano and Navarre not always a reliable that are tolerant to cavity spot nematicide needs to be applied • Deep ploughing buries sclerotes formed on the indicator of whether a • Preplant fumigation with 1,3- • Do not allow carrots to become over mature soil surface nematicide needs to be dichloropropene, 1,3-dichloropropene • Check at www.apvma.gov.au to determine • Metalaxyl will reduce pythium diseases applied + chloropicrin, fenamiphos or metham which fungicides are registered for controlling when used at, or shortly after, seeding. If • Preplant fumigation with sodium. Minimise use due to the potential sclerotinia used frequently, metalaxyl may become 1,3-dichloropropene, for enhanced microbial degradation ineffective due to enhanced microbial 1,3-dichloropropene + • Post harvest losses are minimised by reducing Carrot virus Y (CarVY) mechanical damage during harvesting, by degradation chloropicrin, fenamiphos rapid cooling and storing carrots at 0°C • High soil pH can suppress cavity spot, or metham sodium. If CarVY is a serious disease, spread by however enhanced microbial degradation these chemicals are aphids and occuring throughout Australia. Cavity spot, damping off and root forking develops more rapidly on soils with high pH. used frequently they It infects carrots at any stage and is most Cavity spot is a widespread problem in Australia. Maintain soil pH in the range 6.5-7 in water may become ineffective Symptoms of root knot severe where carrots are grown all-year- nematode. because of enhanced round. It is particularly severe when carrots are grown (5.8-6.3 in CaCl2) microbial degradation with limited rotation. Affected carrots have small • When P. sulcatum is present, rotate carrots The leaves of brown spots (usually less than 10mm in diameter) with unrelated crops e.g. broccoli, lettuce • Use a bare fallow between susceptible infected plants on the surface. Cavity spot develops rapidly on and onions. Where P. violae is present crops develop a mild carrots that are close to harvest or over mature. rotate carrots with non-hosts e.g. onions, • Rotate carrots with a non-host crop. The feathery mottle. Cavity spot is a fungal disease caused by either maize, potatoes and beans choice of non-host will depend on which The most severe Pythium sulcatum or Pythium violae. Pythium Root knot nematode Meloidogyne sp. is present symptoms are sulcatum occurs throughout all carrot growing • Where Meloidogyne javanica is present, stunted and Carrots are very susceptible to root knot regions of Australia. Pythium violae only occurs seed carrots in winter distorted roots, along the River Murray and in South Australia. nematode. This is a serious soil borne disease which occur when that is diffi cult to control and symptoms include Root lesion nematode young plants are Seedling infection by pythium is a common cause root forking and galling. Infection is usually Root lesion nematode causes reddish and infected. of damping off. patchy within a crop; plants are uneven and brown patches on tap and lateral roots. The Disease cycle Tap root infection is a cause of root forking. wilt easily. mature carrots are stunted. CarVY is diffi cult Symptoms of carrot virus Y. There are several species of root knot Symptoms of root to control on farms nematode that infect carrots in Australia. lesion nematode: where carrots The most common species is Meloidogyne the two seedlings on the left are planted sequentially all year because javanica, which occurs in South Australia, have reddish infected volunteer carrots and adjacent crops Victoria and Western Australia. Other species patches caused provide inoculum sources for new crops. include M. hapla which is found in Victoria and by nematode Western Australia, while M. fallax occurs in infection, the two CarVY is spread non-persistently by aphids, seedlings on the Tasmania. right have healthy i.e. the aphids acquire the virus rapidly when roots. feeding on infected leaves, but rapidly lose it when feeding on healthy plants. Symptoms of cavity spot. Your levy @ work VEGEnotes Carrot Diseases If slightly infected carrots are harvested the rot Disease cycle Disease cycle The four species of root lesion nematode continues to develop during storage and can Pythium spp. are soil borne pathogens that Root knot nematodes are diffi cult to control in Australia that infect carrots are: spread to adjacent carrots. persist as resting spores between crops. because they have wide host ranges. They Pratylenchus crenatus, P. neglectus, P. are more usually a problem in sandy soil. penetrans and P. thornei. These carrots then develop a soft, watery, slimy Pythium sulcatum only infects carrots and Root knot nematodes survive between crops rot at the crown. A white cottony fungus develops closely related plants, it can survive for at least Disease cycle on alternate hosts and in egg masses in the from this rot; it often contains small black two years between carrot crops. Pythium Like root knot nematodes, Pratylenchus are soil. sclerotes that look like mouse droppings. violae has a much wider host range and can diffi cult to control because they have wide Disease cycle survive for at least fi ve years between carrot When conditions are suitable, the eggs hatch host ranges, including cereal nurse crops. crops. and juvenile nematodes penetrate root tips. They are a problem in sandy soils and Sclerotinia is a common and widespread soil Female nematodes mature within the roots survive between crops either on alternate Cavity spot caused by Pythium sulcatum is borne pathogen, with a host range that includes and a gall develops around the nematode. hosts or as eggs in the soil. most severe in summer and autumn harvested both commercial crops and weeds. Black, hard These females lay eggs into a gelatinous crops, while cavity spot caused by Pythium When conditions are suitable, the eggs hatch sclerotes form on infected plant debris and these matrix on the root surface. The eggs either violae is most severe in winter harvested and juvenile nematodes penetrate carrot persist in the soil for up to fi ve years. hatch immediately or become dormant. crops. roots. The nematodes migrate and multiply Sclerotes close to the soil surface infect old Control within the roots. leaves and petioles. The infection spreads down Control • Soil sampling to assess the petioles to the crown, resulting in rotting at • Cavity spot control is diffi cult on farms with Control nematode numbers the top of the roots. limited rotation • Sample soil to assess nematode numbers before seeding is before seeding to determine whether a Control • Grow varieties such as Stefano and Navarre not always a reliable that are tolerant to cavity spot nematicide needs to be applied • Deep ploughing buries sclerotes formed on the indicator of whether a • Preplant fumigation with 1,3- • Do not allow carrots to become over mature soil surface nematicide needs to be dichloropropene, 1,3-dichloropropene • Check at www.apvma.gov.au to determine • Metalaxyl will reduce pythium diseases applied + chloropicrin, fenamiphos or metham which fungicides are registered for controlling when used at, or shortly after, seeding. If • Preplant fumigation with sodium. Minimise use due to the potential sclerotinia used frequently, metalaxyl may become 1,3-dichloropropene, for enhanced microbial degradation ineffective due to enhanced microbial 1,3-dichloropropene + • Post harvest losses are minimised by reducing Carrot virus Y (CarVY) mechanical damage during harvesting, by degradation chloropicrin, fenamiphos rapid cooling and storing carrots at 0°C • High soil pH can suppress cavity spot, or metham sodium. If CarVY is a serious disease, spread by however enhanced microbial degradation these chemicals are aphids and occuring throughout Australia. Cavity spot, damping off and root forking develops more rapidly on soils with high pH. used frequently they It infects carrots at any stage and is most Cavity spot is a widespread problem in Australia. Maintain soil pH in the range 6.5-7 in water may become ineffective Symptoms of root knot severe where carrots are grown all-year- nematode. because of enhanced round. It is particularly severe when carrots are grown (5.8-6.3 in CaCl2) microbial degradation with limited rotation. Affected carrots have small • When P. sulcatum is present, rotate carrots The leaves of brown spots (usually less than 10mm in diameter) with unrelated crops e.g. broccoli, lettuce • Use a bare fallow between susceptible infected plants on the surface. Cavity spot develops rapidly on and onions. Where P. violae is present crops develop a mild carrots that are close to harvest or over mature. rotate carrots with non-hosts e.g. onions, • Rotate carrots with a non-host crop. The feathery mottle. Cavity spot is a fungal disease caused by either maize, potatoes and beans choice of non-host will depend on which The most severe Pythium sulcatum or Pythium violae. Pythium Root knot nematode Meloidogyne sp. is present symptoms are sulcatum occurs throughout all carrot growing • Where Meloidogyne javanica is present, stunted and Carrots are very susceptible to root knot regions of Australia. Pythium violae only occurs seed carrots in winter distorted roots, along the River Murray and in South Australia. nematode. This is a serious soil borne disease which occur when that is diffi cult to control and symptoms include Root lesion nematode young plants are Seedling infection by pythium is a common cause root forking and galling. Infection is usually Root lesion nematode causes reddish and infected. of damping off. patchy within a crop; plants are uneven and brown patches on tap and lateral roots. The Disease cycle Tap root infection is a cause of root forking. wilt easily. mature carrots are stunted. CarVY is diffi cult Symptoms of carrot virus Y. There are several species of root knot Symptoms of root to control on farms nematode that infect carrots in Australia. lesion nematode: where carrots The most common species is Meloidogyne the two seedlings on the left are planted sequentially all year because javanica, which occurs in South Australia, have reddish infected volunteer carrots and adjacent crops Victoria and Western Australia. Other species patches caused provide inoculum sources for new crops. include M. hapla which is found in Victoria and by nematode Western Australia, while M. fallax occurs in infection, the two CarVY is spread non-persistently by aphids, seedlings on the Tasmania. right have healthy i.e. the aphids acquire the virus rapidly when roots. feeding on infected leaves, but rapidly lose it when feeding on healthy plants. Symptoms of cavity spot. Your levy @ work VEGEnotes Carrot Diseases CarVY only infects carrots and closely related Black root rot plants e.g. parsnip, coriander and chervil. Two fungi cause black root rot: Thielaviopsis Control basicola (Chalara elegans) and Chalaropsis • Avoid planting sequential side-by-side crops thielavioides. Roots affected by black root and separate crops by planting non-hosts, rot have large black superfi cial patches on them. These patches are often circular and VEGE such as brassicas, between them notes sometimes surrounded by a matt white halo. • Remove volunteer carrots and harvested carrot crops promptly Disease cycle Your levy @ work • Use a fallow period to break the infection The fungi that cause black root rot have a cycle wide host range and occur in soil. Carrots are likely to be contaminated with these fungi in Management of Carrot Diseases Common post-harvest diseases the fi eld before harvest. Bacterial soft rot Common leaf diseases • Use seed that has been treated with After harvest the fungi infect carrots through fungicide This is a soft, slimy, orange rot that can occur wounds or abrasions. Leaf blight • Use fungicide sprays, such as chlorothalonil, on any part of the carrot, although it is often They develop rapidly on Leaf blight is an extremely common, quickly copper, difenoconazole, mancozeb, metiram associated with the eyes. The rot can penetrate carrots stored at 25°C spreading fungal disease that initially occurs and zineb. Start the spraying program when deeply. It does not usually smell unpleasant and in high humidity. as patches within crops. The symptoms of the fi rst sign of blight appears unless there is secondary infection caused by Control leaf blight are small brown, dead spots on the other bacteria. Common root diseases • Losses caused by leaves and petioles (leaf stalks). These spots Soft rot is caused by black root rot can be grow rapidly and eventually join so that the Sclerotinia or cottony rot leaf yellows and dies. The petioles also break either Erwinia carotovora minimised by rapid Sclerotinia is a common fungal disease that during harvesting. subspecies carotovora or cooling of harvested affects many vegetables. It E. carotovora subspecies carrots and storing There are two types of leaf blight, Alternaria affects carrots both in the atroseptica. them at 0°C and Cercospora. Alternaria leaf blight is fi eld and in storage and Disease cycle • Minimise mechanical Symptoms of black caused by Alternaria dauci and/or A. radicina is caused by the fungus root rot. damage during and usually fi rst appears on the oldest Sclerotinia sclerotiorum. Erwinia spp. are common leaves. Cercospora leaf blight is caused harvesting and in the packing shed In the fi eld, the fi rst soil bacteria that survive on by Cercospora carotae and appears on the symptoms are water- crop residues. Carrots are Sclerotinia rot or cottony rot youngest leaves fi rst. likely to be contaminated soaked spots at the base with soft rot bacteria in See Sclerotinia above. Disease cycle of the petioles and at the fi eld before harvest. Further Information Both Alternaria and Cercospora can be carried the crown. The outer Symptoms of bacterial However, these bacteria on carrot seeds and once introduced into an leaves redden and wilt. soft rot. Dr Elaine Davison are readily spread in area will survive on carrot debris. They can There is often a white, Department of Agriculture Western Australia washing water during post- spread easily during rain or irrigation and can cottony fungal growth ph: (08) 9368 3690 harvest handling. also be carried on machinery. in the surrounding soil. email: [email protected] Eventually the top of the Soft rot bacteria enter carrots through wounds, Control Acknowledgements carrot becomes soft and but they can also be forced into the eyes if warm • Disease control is diffi cult on farms where slimy. carrots are dumped into deep cold water tanks. Dr Elaine Davison carrots are planted sequentially Once the bacteria are in the carrot root they Allan McKay • Some carrot varieties are more tolerant of cannot be killed by sanitisers such as chlorine. Dr Roger Jones Symptoms of sclerotinia. leaf blight than others