17 Carrot Diseases You’re Most Likely to Encounter
Carrot diseases are either root-based or foliar-based and there are quite a few to go around depending on your soil and weather conditions.
Both are a problem. Foliar diseases will attack the upper leaves and stems which reduces photosynthesis and will result in fewer or smaller carrots come harvest time.
Root diseases are often caused by soil-dwelling organisms and can spread through the soil or after harvest in storage.
Most diseases that affect carrots are fungal or bacterial and infections can occur in the garden or during storage. But there are also a couple of viral infections I will discuss too, although more rare.
In this article, I’ll discuss the 11 most common diseases that affect carrot roots and the 5 that affect foliage including:
How to identify them;
What causes them; and
What you can do to prevent or minimize them
Of course, the only sure way to tell what disease is attacking your carrots is to send a sample to a diagnostic lab. I’m pretty sure every state has them and they’re usually located at a university in my experience.
Aster Yellows
Source: University of Saskatchewan
Disease Type: Bacteria
Affects: Foliage
Symptoms: Leaves turn yellow and may grow twisted. Taproot may start producing fibrous side roots, but this is less common.
Causes: Spread by aster leafhoppers
Control Methods: The best thing you can do is prevent it by using row covers that prevent leafhoppers from accessing your garden. If you see any affected plants, remove them from your garden and dispose of them. If you already have leafhoppers in your carrots, I’ve used pyrethrin concentrate and it works pretty well.
Occurrence Frequency: Very Common
Safe to Eat: No, I wouldn’t. I’ve heard they taste very unpleasant and bitter after being infected.
Black Root Rot (Black Mold)
Source: University of Massachusetts
Disease Type: Fungi
Affects: Root (mostly crown and upper taproot)
Symptoms: Symptoms are black lesions in random patterns on taproot. Lesions can be brown or black and limited to the skin only. Lesions do not penetrate through the carrot.
Symptoms most commonly do not appear until after harvest and during storage. In rare cases, it can cause blight on leaves.
Causes: Growing in overly rich organic or mucky soils; easily infected from wounds on roots during harvesting. This disease occurs in wet, humid conditions with temperatures over 68 degrees Fahrenheit.
Control Methods: Use caution when harvesting so that you do not wound the carrot taproot. Do not store in warm temperatures.
Practice good crop rotation. This fungus can remain in the soil for up to 8 years. Avoid planting carrots, celery, parsnip, or dill in locations where you have found black root rot.
Plant in raised beds with well-draining soil. Avoid wounding roots when thinning and harvesting. This fungus invades wounded tissues. Wash well before storing and store harvested carrots in cool temperatures.
Red Cored Chantenay carrots are more resistant to this disease. If you’ve had a problem with root rot in the past, consider planting this carrot.
An organic fungicide can also reduce disease levels. I prefer the one linked here because it’s natural and made with different oils. It’s safe for pets, humans, and even ladybugs.
Occurrence Frequency: Common
Safe to Eat: No, do not eat carrots with black rot. Dispose of them immediately.
Cavity Spot
Source: University of California
Disease Type: Fungi (soil-borne)
Affects: Root (mostly crown and upper taproot)
Symptoms: Appears as rusty-brown lateral formation on the root. Infections can occur during early root development. Cavity spot opens up later near harvest with horizontal sunken lesions on the surface of the root and can make the carrot more susceptible to other fungal or bacterial infections.
Infections typically occur on the upper third of the root but can be anywhere. Lesions may begin as a pinpoint and then enlarge as the root matures.
Sometimes confused with symptoms of flea beetle feeding. Flea beetle damage can be found on leaves as well. If there are no leaf pits, you’re most likely dealing with cavity spot.
Causes: Growing in soil with high peat content or very moist soil, especially with low soil temperatures. Compacted soil creates an environment for these fungi to thrive.
Control Methods: Grow in a raised bed with well-draining soil to prevent and practice 3-year crop rotations. Do not overwater carrots. Harvest mature carrots as soon as possible as older ones are more susceptible to this disease. Do not leave them in the ground.
This fungus can live in the soil for up to 3 years. If found, plant non-host plants such as tomatoes, watermelons, corn, or potatoes instead of carrots for the next 3 years in this location.
Occurrence Frequency: Common
Safe to Eat: No, do not eat carrots with cavity spots. Dispose of them immediately.
Root Dieback
Source: University of California
Disease Type: Fungi (water/soil-borne)
Affects: Root
Symptoms: Seedlings fall over and die after emerging. Stems may be unusually dark and shriveled at the soil line. The disease typically kills taproots in less than 2 weeks after germination. May cause forked roots.
Causes: Growing in extremely wet soils with high temperatures will foster this disease.
Control Methods: Maintain uniform soil moisture at the seed depth until seedlings emerge, plant in raised beds with well-draining soil and companion plant to keep the soil as cool as possible during hotter months.
Occurrence Frequency: Less Common
Safe to Eat: It won’t matter, your carrots will die young. There’s nothing to eat.
Common Scab
Source: Bayer Crop Science
Disease Type: Fungi
Affects: Root
Symptoms: Leaves horizontal lesions on carrot taproots. Can cause raised or sunken lesions that resemble a cork. No visual symptoms on leaves.
Causes: Growing in alkaline soils with overly rich organic material. This fungus thrives in hot, dry summer climates.
Control Methods: If soil pH is above 7, take steps to lower it. I prefer to use sulfur because it is a naturally occurring mineral. Practice crop rotation and do not plant carrots in the soil where potatoes were recently grown. This disease is soil-borne and potatoes are another host.
Do not apply lime before sowing carrot seeds, this will create a favorable environment for this fungus.
Occurrence Frequency: Common
Safe to Eat: No, do not eat carrots with scab on them.
Alternaria Leaf Blight
Source: Cornell University
Disease Type: Fungi (seed/residue-borne)
Affects: Foliage
Symptoms: Very destructive disease that first appears along leaflet margins as greenish-brown. Enlarges to brown or black in color. Older leaves are more susceptible to infection. When 40% of the leaf is infected, the leaves yellow and the plant will collapse and die.
Causes: Growing in frequently wet, humid weather can lead to this disease. It is a very common leaf disease in carrots and parsley.
Control Methods: Practice good crop rotation and buy high-quality seeds that are disease-free. Shin Kuroda and Red Cored Chantenay carrot varieties are more resistant to this disease.
If disease breaks out use an organic fungicide. I prefer the one linked here because it is made with natural oils and citric acid, and it’s safe for people and pets. Because it is seed-borne, do not save seeds from this plant.
Remove infected plants asap and destroy the diseased material.
Occurrence Frequency: Very Common
Safe to Eat: I’ve been told that because leaf blight only affects the foliage and not the root, you can still eat the carrot. It just might be a small carrot. If you’re unsure, I would consult someone at your local university ag extension.
Cercospora Leaf Spot
Source: Cornell University
Disease Type: Fungi (seed/residue-borne)
Affects: Foliage
Symptoms: Very destructive disease that leaves lesions on carrot leaf stems and eventually kills the plant.
Infection first appears as brown or black spots with yellow margins. As it progresses, leaflets become yellow and curl at the margins. Unlike leaf blight, leaf spot typically affects younger leaves first, not older ones.
Symptoms can occur on carrot tissue above the ground but this is more rare. It is usually most severe among leaflet margins.
Causes: Seed-borne disease that can spread by wind or splashing water.
Control Methods: Practice good crop rotation and use organic fungicidal treatment if necessary. Keep foliage as dry as possible and avoid overhead sprinklers or splashing water. Water carrots using furrow irrigation.
Remove infected plants asap and destroy the diseased material.
Occurrence Frequency: Common
Safe to Eat: I’ve been told that because the leaf spot only affects the foliage and not the root, you can still eat the carrot. It just might be a small carrot. If you’re unsure, I would consult someone at your local university ag extension.
Sclerotinia Rot (White Mold)
Source: University of Massachusetts
Disease Type: Fungi (soil-borne)
Affects: Root
Symptoms: Symptoms noticeable after washing and storing. Inside of the carrot may look black while the outside of the carrot begins to be covered in fluffy white mold with black structures on it. The mold can appear soft and wet.
Fungus moves rapidly from one carrot to the next from spores that are passed to the carrot during growth.
Occasionally infection kills stems while in the garden and extensive decay can occur before symptoms of wilt appear on the upper part of the plant.
Causes: Growing in wet soil with high temperatures will foster this fungus.
Control Methods: Prevention is the best control method. Plant in raised beds with good soil drainage and use furrow irrigation. Avoid overhead sprinklers.
Thin and space carrot plants appropriately. Good air circulation will help minimize a disease outbreak.
If you have an outbreak, spores can persist in the soil for several years and they overwinter well.
Many vegetables are a host for white mold. One non-host plant I’ve found is onions, but there are few crop rotations you can do if you have this in your soil.
One option is to solarize your soil which will kill the fungus, but keep in mind it will kill all the good organisms too. You’ll have to start over by fixing your soil before planting next season.
When storing carrots, store them at low temperatures to minimize the risk of mold exposure. It can spread through containers.
Occurrence Frequency: Very Common
Safe to Eat: No, do not eat carrots with white mold on them.
Bacterial Leaf Blight
Source: University of Massachusetts
Disease Type: Bacteria (seed-borne)
Affects: Foliage
Symptoms: Similar to leaf spot and fungi leaf blight. Symptoms appear on leaf margins as small, yellow spots and later turn brown or black. Leaflets become distorted and curled and may be brittle.
Causes: Growing in climates with cool, wet weather and frequent rain storms favor this disease.
Control Methods: Buy high-quality seeds to prevent this. Remove diseased plants immediately and destroy them. Avoid overhead watering and consider mulching to prevent bacteria from being spread through water splashing from the soil.
If you have a large outbreak, using the Monterey Bactericide for organic gardens is effective.
Planting a disease-resistant variety such as Atomic Red can help minimize outbreaks.
Occurrence Frequency: Common
Safe to Eat: I’ve been told that because leaf blight only affects the foliage and not the root, you can still eat the carrot. It just might be a small carrot. If you’re unsure, I would consult someone at your local university ag extension.
Bacterial Soft Rot
Source: Plantwise Knowledge Bank
Disease Type: Bacteria (soil/water-borne)
Affects: Root
Symptoms: Symptoms start small with lesions that quickly spread and cause the root to become mushy. Skin may remain intact, but the flesh underneath becomes liquified.
Taproot often becomes soft, watery, and slimy, eventually the bacteria will consume the core of the carrot. A foul odor may be associated with this disease.
Can cause yellowing or wilting of foliage above the ground as well.
Causes: Growing in poorly draining soils and warm weather with standing water fosters this bacteria. Wounded roots create more exposure to infection.
Control Methods: Plant in raised beds with well-draining soil. Avoid wounding roots when thinning and harvesting. Wash well before storing and store harvested carrots in cool temperatures.
Occurrence Frequency: Common
Safe to Eat: No, do not eat carrots with bacterial soft rot.
Crown Rot and Fusarium Dry Rot
Source: University of Massachusetts
Disease Type: Fungi (soil-borne)
Affects: Root
Symptoms: Early symptoms include horizontal dark brown lesions around the root crown. As the disease progresses, the carrot tops may die in patches throughout your garden.
Lesions form large, deep, rotten areas on the top of the root.
Symptoms may not occur until after storage.
Causes: This disease favors moist conditions.
Control Methods: Plant in raised beds with well-draining soil. Avoid wounding roots when thinning and harvesting and always use clean, sanitized garden tools.
Harvest carrots early and practice good crop rotation. Avoid planting in places where the disease occurred.
Store harvested carrots in cool temperatures.
Occurrence Frequency: Less Common
Safe to Eat: No, do not eat carrots with crown rot.
Rubbery Brown Rot and Violet Root Rot
Source: Springer Link
Disease Type: Fungi
Affects: Root
Symptoms: Symptoms include partially rotten, leathery textured roots which may be purple in color. Often found in patches throughout your garden.
Causes: This disease favors humid climates.
Control Methods: Practice good crop rotations and use organic fungicides as needed.
Occurrence Frequency: Less Common
Safe to Eat: No, do not eat carrots with rubbery brown rot.
Root Knot Nematodes
Source: Hawaii Master Gardener Program
Disease Type: Roundworm
Affects: Root
Symptoms: Symptoms include forked and stunted roots with round galls (ball-looking things).
Causes: Nematodes aren’t technically a disease, they’re a carrot pest, but they favor cool, wet springs.
Control Methods: Use a biodegradable, natural nematode treatment or solarize your soil to kill root knot nematodes.
Occurrence Frequency: Very Common
Safe to Eat: No, do not eat carrots with nematode damage.
Heat Canker
Source: Gardener's Supply
Disease Type: Unknown
Affects: Root
Symptoms: Symptoms include tissues of the root near the soil surface collapsing and dying. Takes the appearance of disfigurement that can almost look like the carrot is melting.
Causes: Direct sunlight causes the root to disfigure.
Control Methods: Keep carrot roots covered and avoid black or dark soils that can lead to this injury. Mulch can help prevent this injury as well.
Occurrence Frequency: Less Common
Safe to Eat: No, do not eat carrots with heat canker.
BLTVA (Beet Leafhopper Transmitted Virescence Agent)
Source: University of California
Disease Type: Phytoplasma-like Organism
Affects: Root
Symptoms: Symptoms include reddish-purple leaves. Infected plants can prematurely bolt with flowers turning green instead of white. Diseased carrots have woody roots with several lateral roots and can look hairy.
Causes: Transmitted by beet leafhoppers.
Control Methods: Clear weeds and debris that harbor leafhoppers. Destroy infected plants as soon as possible.
Occurrence Frequency: Common
Safe to Eat: No, do not eat carrots with bltva.
Powdery Mildew
Source: Bayer Crop Science
Disease Type: Fungi
Affects: Foliage
Symptoms: Symptoms start with small, circular white spots that enlarge into a white powdery substance that covers the leaves. The powder is spore structures that spread the disease.
As disease spreads, it can cause yellowing on leaves as well.
Causes: Powdery mildew favors hot dry summers with cool nights.
Control Methods: Plant in unshaded areas whenever possible and provide the right amount of water. Do not over-fertilize.
When spotting an infected plant, prune the infected area and discard the diseased leaflets as soon as they appear to prevent the disease from spreading.
If powdery mildew has already spread throughout your garden, I used to use sulfur, but found that it impacted the soil pH too much. The best thing I’ve found is the Grow Safe Bio Fungicide which will reduce powdery mildew significantly.
Powdery mildew can overwinter on crop debris. Clear any debris and practice good crop rotation. Do not plant carrots, celery, parsnips, or parsley in the same location where powdery mildew was found.
Red Cored Chantenay and Danvers 126 have shown signs of resistance to powdery mildew. If you have a problem with this fungus, try planting these carrot varieties.
Occurrence Frequency: Extremely Common
Safe to Eat: It’s safe to eat the root, but I would not eat the carrot greens. Powdery mildew is not toxic to humans but can cause allergic reactions in some people. Consult a doctor.
Carrot Motley Dwarf Virus and Carrot Red Leaf Virus
Source: University of California
Disease Type: Virus
Affects: Foliage
Symptoms: Infection begins in the seedling stage with foliage turning yellow, orange, or red in color. Plants may experience stunted growth. Some leaves may remain green.
Results in stunted carrot growth.
Causes: Typical occurs in cooler, spring weather and is a combination of carrot redleaf virus and carrot mottle virus. This virus is transmitted by willow-carrot aphids and green peach aphids.
Control Methods: Overwintered carrots are a source of subsequent spring carrot motley dwarf development so harvest carrots early and do not leave them in the ground over winter.
Take measures to attract aphid natural predators or use an insecticidal soap to control aphid populations.
Occurrence Frequency: Very Common
Safe to Eat: Unknown
Carrot Disease FAQ
What are the most common diseases in carrots?
Different fungi and bacteria thrive in different host environments so depending on where you live, you may combat different diseases. In the US, the most common carrot diseases include powdery mildew, aster yellows, leaf blight, and white mold.
What are the symptoms of carrot blight?
Blight is a common disease found on carrots and can be very destructive. It first appears along leaflet margins as greenish-brown and then enlarges to become brown or even black. Once 40% of the leaf is infected, the leaves yellow and the plant collapses.
Are some carrots more resistant to diseases?
Yes, Danvers 126, Shin Kuroda, Red Cored Chantenay, and Atomic Red are some of my favorite types of carrots to grow that are resistant to many carrot diseases.
