Various root rots of carrots. Dr. Caterina Saude and Dr. Mary K. Hausbeck, Department of Plant Pathology, Michigan State University, Carrot Country, Summer 2006

Bacterial blight

Disease: Bacterial blight
Pathogen: Xanthomonas hortorum pv. carotae (formerly Xanthomonas campestris pv. carotae)

bacterial leaf blight of a carrot 1 — **Photo Source:** Lindsey du Toit, Washington State University

bacterial leaf blight of carrot 2 — **Photo Source:** Lindsey du Toit, Washington State University

bacterial leaf blight 3 — **Photo Source:** Lindsey du Toit, Washington State University

bacterial leaf blight of carrot 4 — **Photo Source:** Lindsey du Toit, Washington State University

bacterial leaf blight of carrot 5 — **Photo Source:** Lindsey du Toit, Washington State University

bacterial leaf blight of carrot 6 — **Photo Source:** Lindsey du Toit, Washington State University

bacterial leaf blight of carrot 7 — Close-up view of bacterial blight lesions showing watersoaking and chlorosis around the lesions.
**Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

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Bacterial soft rot

Disease: Bacterial soft rot
Pathogen: Various bacteria including Dickeya spp. and Pectobacterium spp. (formerly Erwinia spp.)

bacterial soft rot on carrot-2 — Soft rot of the root of a plant in a carrot seed crop following early spring cold injury to the roots.
**Photo Source:** Bo-Ming Wu, Oregon State University

wilting of carrot foliage due to soft rot. — Wilting of foliage in a carrot seed crop as a result of soft rot of the roots preventing adequate translocation of water to the foliage.
**Photo Source:** Bo-Ming Wu, Oregon State University

bacterial soft rot on carrot in a field — Severe wilting and dieback of plants in a carrot seed crop as a result of soft rot of the roots.
**Photo Source:** Bo-Ming Wu, Oregon State University

Bacterial soft rot of a carrot root-3 — Death of plants in the female row of a hybrid Kuroda carrot seed crop as a result of bacterial soft rot.
**Photo Source:** Jeremiah Dung, Oregon State University

Bacterial soft rot of a carrot root-4 — A plant wilting and dying in a carrot seed crop as a result of soft rot of the root. Note the black lesion extending up the stem from the soil line.
**Photo Source:** Jeremiah Dung, Oregon State University

Bacterial soft rot of a carrot root-5 — Black lesion extending up the stem from the soil line as a result of infection by Pectobacterium carotovorum.
**Photo Source:** Lindsey du Toit, Washington State University

Bacterial soft rot of a carrot root-6 — Symptoms of bacterial soft rot of carrot roots.
**Photo Source:** Jeremiah Dung, Oregon State University

bacterial soft rot on carrot-3 — Severe pitting of carrot roots caused by soft rot bacteria, observed after the roots were harvested and washed.
**Photo Source:** Lindsey du Toit, Washington State University

Bacterial soft rot of a carrot root 2 — Severe pitting of carrot roots caused by soft rot bacteria, observed after the roots were harvested and washed.
**Photo Source:** Lindsey du Toit, Washington State University

Bacterial soft rot of a carrot root — Severe pitting of carrot roots caused by soft rot bacteria, observed after the roots were harvested and washed.
**Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Soft Rot {Core Soft Rot}.

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Black root rot

Disease: Black root rot
Pathogen: Thielaviopsis basicola (= Chalara elegans)

Online Resources:

Black root rot. University of Massachusetts Amherst, Agriculture & Landscape Program, Vegetable Program, Soil, Crop & Pest Management.

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Black rot

Disease: Black rot
Pathogen: Alternaria radicina

Black rot on carrot-2 — **Photo Source:** Pacific Northwest seed company field representative

Black rot on carrot-3 — **Photo Source:** Pacific Northwest seed company field representative

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Black Rot.

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Cavity spot

Disease: Cavity spot
Pathogen: Pythium spp. such as P. violae and P. sulcatum

symptoms of cavity spot on carrot-2 — **Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Cavity Spot.

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Cercospora leaf spot

Disease: Cercospora leaf spot
Pathogen: Cercospora carotae

symptoms of leaf spot — **Photo Source:**D.A. Inglis

symptoms of cercospora leaf spot on carrot stalk — **Photo Source:** Lindsey du Toit, Washington State University

cercospora leaf spot on carrot leaves — **Photo Source:** Lindsey du Toit, Washington State University

leaf spot on carrot — **Photo Source:**D.A. Inglis

cercospora leaf spot symptoms — **Photo Source:** Lindsey du Toit, Washington State University

Closeup of cercospora leaf spot on carrot — **Photo Source:** Lindsey du Toit, Washington State University

cercospora carotae under microscope-1 — **Photo Source:** Lindsey du Toit, Washington State University

cercospora carotae under microscope-2 — **Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Cercospora Leaf Blight.
Carrot: Leaf spot, Washington State University.
Carrot Leaf Blight, Vegetable MD Online, Cornell University.
Leaf Blights or Spots of Carrot (pdf), Universion of Illinois Extension.
Management of Carrot Leaf Diseases, Ontario Ministry of Agriculture, Food and Rural Affairs.

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Phytoplasma and spiroplasma infection

Disease: Phytoplasma and spiroplasma infection (e.g., aster yellows)
Pathogen: Various types of phytoplasmas and spiroplasma, e.g., Aster yellows phytoplasma, Beet leafhopper transmitted virescence agent (BLTVA), and Spiroplasma citri

Aster yellow on carrot-1 — **Photo Source:** G.Q. Pelter

Aster Yellows on carrot-5 — Symptomatic (left) vs. asymptomatic (right) parts of an umbel from a carrot seed crop as a result of infection by a phytoplasma.
**Photo Source:** Lindsey J. du Toit

Aster Yellows on carrot-2 — **Photo Source:** G.Q. Pelter

Aster Yellows on carrot-3 — Phytoplasma infection of carrot showing hairy roots and purple-bronze foliage.
**Photo Source:** Lindsey J. du Toit

Aster Yellows on carrot-4 — Normal carrot seed umbels (left) vs. umbels showing symptoms of phyllody and virescence (right) as a result of infection by a phytoplasma.
**Photo Source:** Lindsey J. du Toit

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Aster Yellows.
Aster leafhoppers in carrots, Live barley near carrots when leafhoppers may be present increases the number of leafhoppers and their potential to spread aster yellows phytoplasma. Integrated Pest Management Resources, Michigan State University.

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Powdery mildew

Disease: Powdery mildew
Pathogen: Erysiphe heraclei

powdery mildew on carrot-2 — **Photo Source:** Lindsey du Toit

powdery mildew on carrot-3 — **Photo Source:** Lindsey du Toit

powdery mildew on carrot-4 — **Photo Source:** E. J. Sorensen

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Powdery Mildew.

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Rhizoctonia

Disease: Rhizoctonia
Pathogen: Rhizoctonia solani

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Violet root rot

Disease: Violet root rot
Pathogen: Rhizoctonia crocorum (sexual stage = Helicobasidium brebissonii)
Host crops: Violet root rot has been reported on carrot, celery, fennel, parsley, and parsnip within the Umbelliferae. However, the fungus reportedly has a wide host range that includes asparagus, artichoke, alfalfa, bean, beet, cabbage, clover, dandelion, mangel, potato, rape, rhubarb, sugar beet, sweet potato, and turnip as well as numerous weed species.

violet root rot on carrot-2 — Close-up view of severe violet root rot on a carrot. Note the fan-like hyphae of the pathogen, *Rhizoctonia crocorum,* growing on the root surface.
**Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

Carrot – Violet root rot – PNW Handbooks.
Carrot – Violet root rot – Identification and Management of Carrot Root Diseases, Factsheet. Ontario.

White mold

Disease: White mold (=Cottony rot)
Pathogen: Sclerotinia sclerotiorum
Host crops: Bean, various brassica vegetables, carrot, eggplant, lettuce, potato, tomato, etc.

dieback of carrot from whitemold — Dead and dying plants in a carrot seed crop infected with white mold.
**Photo Source:** Lindsey du Toit, Washington State University

white mold on carrot root — **Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) Cottony Rot.
Carrot: Cottony Rot (White Mold) (pdf). Howard F. Schwartz and David H. Gent, Colorado State University.
See Diseases, pests, and other problems common to many vegetables: White mold.

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Nematodes

Root knot

Disease: Root knot
Pathogen: Meloidogyne species
Host crops: Numerous plant species, including many vegetables such as carrot, coriander, onion,
potato, etc.

galls cause by root knot nematode — Galls caused by root knot nematode.
**Photo Source:** Lindsey du Toit, Washington State University

showing resistant vs. susceptible cultivar — The root of a carrot cultivar partially resistant to root knot nematode (left) vs. the root of a highly susceptible cultivar (right).
**Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Carrot (Daucus carota) – Nematode, Root-knot.
Carrot: Root-knot nematode, Washington State University Hortsense.
Major Emerging Problems with Minor Meloidogyne Species (pdf). By Axel A. Elling, Washington State University, Phytopathology Review.
See Diseases, pests, and other problems common to many vegetables: Root knot.

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Insect/Mite Pests

Carrot rust fly

Common name: Carrot rust fly
Latin binomial: Psila rosae
Host crops: Carrot, parsnip, celeriac, celery, turnip and other umbelliferous crops, including the weed, hemlock.

Online Resources:

Vegetable crop pests-Carrot rust fly. Pacific Northwest Insect Management Handbook, Oregon State University.
Carrot Rust Fly Biology & Management. Nick Andrews, Small Farms, Oregon State University.
Carrot: Carrot rust fly, Use IPM (Integrated Pest Management) for successful plant problem management. Hortsense, Carrie Foss, Pesticide Education, Art Antonelli, Extension Entomology, WSU Puyallup.
Managing Carrot Rust Fly – In Search of Alternatives for a Tough Customer (pdf). Dr. David Muehleisen, Andrew Bary, Dr. Craig Cogger, Dr. Carol Miles, Amanda Johnson and Dr. Marcia Ostrom, WSU, and Terry Carkner, Terry’s Berries Organic Farm, Agrichemical and Environmental News, March 2003.
Intercropping in Carrots for Rust Fly Control. Carol Miles, Ph.D.,WSU Extension, Leslie Zenz, Research Assistant, Betsie DeWreede, Owner, Independence Valley Farm, and Julie Puhich, Owner, Common Ground CSA, Mount Vernon Northwestern Washington Research and Extension Center, Vegetable Research and Extension.
Carrot Rust Fly – Life Cycle and Habits. Carrot Insects, Ontario Ministry of Agriculture, Food and Rural Affairs Factsheet 93-077.
Carrot rust fly (pdf). Plant Health Australia Factsheet.

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Lygus bugs

Common name: Lygus bugs
Latin binomial: Lygus spp.
Host crops: Numerous different species of vegetables and other crops, e.g., alfalfa, beet, cabbage, carrot, potato, spinach, Swiss chard, etc. Lygus bugs can cause different types of damage to various growth stages of different crops. They cause blackheart on celery, blasting on flower tissues, collapse of asparagus spears, decreased yields in carrot, beet, spinach, and other seed crops, etc.

people sweeping for lygus bug — Sweeping for lygus bugs in a carrot seed crop during bloom to determine appropriate management practices.
**Photo Source:** Lindsey du Toit, Washington State University

lygus bug on a Swiss chard plant-3 — A lygus bug on a Swiss chard plant. Note the wing pads developing on the insect.
**Photo Source:** Bev Gerdeman, WSU Entomologist

Online Resources:

Pacific Northwest Insect Management Handbook: Carrot seed – Lygus bug.

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Spider mites

Common name: Spider mites
Latin binomial: Tetranychus spp. including twospotted spider mite (Tetranychus urticae), strawberry spider mite (Tetranychus turkestani), and Pacific spider mite (Tetranychus pacificus)
Host crops: Wide host range, including many vegetables such as bean, carrot seed crops, potato, etc.

spider mite on carrot seed crop — Severe outbreak of spider mites in a carrot seed crop in central Washington.
**Photo Source:** Lindsey du Toit

spider mite symptoms on carrot seed crop — Severe outbreak of spider mites in a carrot seed crop in central Washington.
**Photo Source:** Lindsey du Toit

Eggs of the two-spotted spider mite, Tetranychus urticae. — Eggs of the two-spotted spider mite, *Tetranychus urticae.*
**Photo Source:** Silvia Rondon, Oregon State University

twospotted-spider-mite — Eggs of the two-spotted spider mite, *Tetranychus urticae*.
**Photo Source:** Silvia Rondon, Oregon State University

Online Resources:

Carrot seed – Twospotted spider mite. PNW Insect Management Handbook, Chapter: Vegetable Seed, Section: Carrot Seed.
See Diseases, pests, and other problems common to many vegetables: Spider mites.

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Wireworm

Common name: Wireworm
Latin binomial: Limonius spp. (including L. canus and L. californicus). Other wireworm species including Agriotes spp. and Ctenicera spp. can be pestiferous.
Host crops: Potato, onion, carrot, beet, spinach seed crops, and radish. Other crops, like corn, beans
and peas can be impacted by high densities of wireworms feeding on seedlings resulting in poor crop stands.

Wireworm larvae — **Photo Source:** Lindsey du Toit, Washington State University

click beetle-1 — A click beetle of the species *Agriotes obscurus*, the larvae of which are wireworms.
**Photo Source:** Oregon State University –Oregon State Arthropod Collection.

click beetle-2 — A click beetle of the species *Limonius californicus*, the larvae of which are wireworms.
**Photo Source:** Oregon State University – Oregon State Arthropod Collection.

click beetle-3 — A click beetle of the species *Limonius canus*, the larvae of which are wireworms.
**Photo Source:** Oregon State University – Oregon State Arthropod Collection.

Online Resources:

Vegetable crop pests – Wireworm. PNW Insect Management Handbook.
Wireworms. Ontario Ministry of Agriculture and Food.
Managing Wireworms in Vegetable Crops. VegEdge, University of Minnesota.
Wireworm Field Guide (pdf) – A guide to the identification and control of wireworms, Syngenta Crop Protection Canada, Inc.
Wireworm Biology and Nonchemical Management in Potatoes in the Pacific Northwest, N. Andrews, M. Ambrosino, G. Fisher, and S.I. Rondon, Pacific Northwest Extension Publication no. PNW607.
See Diseases, pests, and other problems common to many vegetables: Wireworm.

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Parasitic Plants

Field dodder

Common name: Field dodder
Latin binomial: Cuscuta spp.
Host Crops: Bean, beet, carrot, onion, pepper, potato, tomato, and many other crops (not only vegetables).

field dodder on carrot-2 — Dodder coiled on carrot leaves.
**Photo Source:** Lindsey du Toit, Washington State University

field dodder on carrot-3 — Dodder on carrot.
**Photo Source:** Lindsey du Toit, Washington State University

field dodder on carrot-4 — Dodder patch.
**Photo Source:** Lindsey du Toit, Washington State University

Online Resources:

See Diseases, pests, and other problems common to many vegetables: Field dodder.

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Abiotic Problems Common to Carrot

Split roots

Problem: Split roots
Cause: Wide fluctuations in soil moisture and growth rate of carrot roots, particularly early in the growth stage. Splitting can lead to secondary bacterial infections.
Crops affected: Beet, carrot, parsnip, radish and other root crops.

severe splitting of a carrot root — Severe splitting of a carrot root.
**Photo Source:** Tom Brown

Online Resources:

See Root vegetables: splitting. Royal Horticultural Society.

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please contact: Lindsey du Toit at dutoit@wsu.edu or at 360-848-6140.

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