Disease Control

Leaf Blight/Spot (Alternaria, Cercospora, or Septoria)     

Leaf spots caused by Alternaria tend to be dark brown and circular or irregular. Spots may or may not have yellow haloes. Spots may enlarge and coalesce, blighting large portions of the leaves.

Cercospora leaf spot typically appears as small, round, tan lesions, often with dark borders. Under humid conditions, small, round, black fruiting bodies may be observed in the lesions with a hand lens. Spots may coalesce, causing leaf blight and defoliation. 

Septoria produces small, tan lesions on leaves and petioles with dark borders and small black specks in the center. Spots may enlarge and coalesce, blighting large portions of the leaves.

These diseases appear very similar in the field, making identification difficult; however, treatment methods are the same for all three. Use certified, disease-free seed or treat seed with hot water or fungicides. Rotate with crops outside of the Apiaceae family. Irrigate early in the day to allow foliage to dry quickly. Use wider plant spacing and/or raised beds to improve air circulation. Plant resistant or tolerant varieties. Apply fungicides based upon a disease forecasting system.

FRAC Group 2:

• iprodione (Rovral 4F): 1 to 2 pt/A; PHI 0d, REI 24h. For Alternaria on carrot only. 

FRAC Group 3:

• azoxystrobin + propiconazole (Quilt Xcel): 14 fl oz/A; PHI 14d, REI 12h, Groups 11 & 3. Carrot only.
• difenoconazole + cyprodinil (Inspire Super): 14 to 20 fl oz/A; PHI 7d, REI 12h, Groups 3 & 9. Carrot only.
• fluopyram + difenoconazole (Luna Flex): 11 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7. Carrot only. Do not make more than 2 sequential applications before rotation with a non-Group 3 or 7 fungicide. 
• propiconazole (Tilt): 3 to 4 fl oz/A; PHI 14d, REI 24h. For Alternaria suppression only. 

FRAC Group 7:

• boscalid (Endura): 4.5 oz/A; PHI 0d, REI 12h. Alternaria only. Do not make more than 2 applications per season. 
• fluopyram + difenoconazole (Luna Flex): 11 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7. Carrot only. Do not make more than 2 sequential applications before rotation with a non-Group 3 or 7 fungicide. 
• fluxapyroxad + pyraclostrobin (Merivon Xemium): 4 to 5.5 fl oz/A; PHI 7d, REI 12h, Groups 7 & 11.
• penthiopyrad (Fontelis): 16 to 30 fl oz/A; PHI 0d, REI 12h.
• pyraclostrobin + boscalid (Pristine): 8 to 10.5 oz/A; PHI 0d, REI 12h, Groups 11 & 7. Do not alternate with other Group 11 fungicides.
• pydiflumetofen + fludioxonil (Miravis Prime): 6.8 fl oz/A; PHI 7d, REI 12h, Groups 7 & 12. See label for graze/feed restrictions.

FRAC Group 9:

• difenoconazole + cyprodinil (Inspire Super): 14 to 20 fl oz/A; PHI 7d, REI 12h, Groups 3 & 9. Carrot only.
• cyprodinil + fludioxonil (Switch 6.25 WG): 11 to 14 oz/A; PHI 7d, REI 12h, Groups 9 & 12. Alternaria only. 

FRAC Group 11:

• azoxystrobin + propiconazole (Quilt Xcel): 14 fl oz/A; PHI 14d, REI 12h, Groups 11 & 3. Carrot only.
• fluxapyroxad + pyraclostrobin (Merivon Xemium): 4 to 5.5 fl oz/A; PHI 7d, REI 12h, Groups 7 & 11.
• pyraclostrobin + boscalid (Pristine): 8 to 10.5 oz/A; PHI 0d, REI 12h, Groups 11 & 7. Do not alternate with other Group 11 fungicides.
• trifloxystrobin (Flint): 2 to 3 oz/A; PHI 7d, REI 12h. Do not graze or feed leaves/foliage of treated crops. Do not alternate with other Group 11 fungicides. 

FRAC Group 12:

• cyprodinil + fludioxonil (Switch 6.25 WG): 11 to 14 oz/A; PHI 7d, REI 12h, Groups 9 & 12. Alternaria only. 
• pydiflumetofen + fludioxonil (Miravis Prime): 6.8 fl oz/A; PHI 7d, REI 12h, Groups 7 & 12. See label for graze/feed restrictions.

FRAC Group 19:

• polyoxin D zinc salt (OSO 5%SC): 6.5 to 13 fl oz/A; PHI 0d, REI 4h.

FRAC Group 29:

• fluazinam (Omega 500F): 16 pt/A; PHI 7d, REI 12h. For Alternaria on carrot only. 

FRAC Group BM01:

• Swinglea glutinosa extract (EcoSwing^OG): 1.5 to 2 pt/A; PHI 0d, REI 4h. Carrot only. Use preventatively. 

FRAC Group BM02:

• Pseudomonas chlororaphis strain AFS009 (Howler EVO^OG): 2.5 to 7.5 lb/A; PHI 0d, REI 4h. Use preventatively.

FRAC Group M01:

• copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h. Carrot only. Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette. An OMRI-listed formulation is available (Kocide 3000-O^OG).

FRAC Group M05:

• azoxystrobin + chlorothalonil (Quadris Opti): 2.4 pt/A; PHI 0d, REI 12h, Groups 11 & M05. See label for tank mix precautions. Carrot only.
• chlorothalonil (Bravo Weather Stik): 1.5 to 2.0 pt/A; PHI 0d carrot, 10d parsnip, REI 12h.

Crater Rot (Rhizoctonia carotae)

Crater rot, caused by the fungus Rhizoctonia carotae, is a postharvest disease of carrot roots that can occur during prolonged cold storage (longer than 30 days). The disease is characterized by long, dark, horizontal legions on stored roots. The pathogen is soilborne and initial infection occurs before harvest. Late-harvested carrots may have higher amounts of infection. The fungus develops in cold storage (39–43°F), especially when there is a film of moisture or very high humidity. 

Under high disease pressure, carrots can be dipped in fungicides or inorganic salts prior to storage. Washing carrots in water can also reduce inoculum clinging to root surfaces. Disinfestation of crates and other equipment minimizes disease development. Proper cold storage that avoids temperature fluctuations and condensation helps reduce disease and prevent dehydration. Removal of carrots from cold storage early can prevent losses.

Bacterial Blight of Carrot (Xanthomonas campestris pv. carotae)

This disease looks very similar to the fungal leaf spots of carrot. Irregular brown lesions on leaves may or may not have yellow haloes. Lesions may appear shiny on the undersides, and a brownish secretion is sometimes observed. Lesions may coalesce, turning large areas brown. Dark streaks may be seen on petioles. In the field, symptoms may occur in small patches that can expand rapidly in wet weather. The bacterium is seed-borne and easily spread by splashing water. Start with clean seed. Rotate away from carrots for at least 2 years. Remove infected plants. Plow in crop residues to hasten crop debris decomposition. 

FRAC Group M01:

• copper octanoate (Cueva^OG): 0.5 to 2.0 gal/100 gal (see label); PHI 0d, REI 4h. See label for crop injury warning.

FRAC Group NC:

• hydrogen peroxide + peroxyacetic acid (OxiDate 2.0^OG) 1:40 dilution (rescue), 1:100 dilution (curative), or 1:200 to 1:400 dilution (preventative); PHI 0d, REI until sprays dry (field), 1h fogging/spraying or 0h other methods (enclosed areas). Do not tank mix with copper.

FRAC Group P07:

• potassium phosphite (Rampart): 1.0 to 3.0 qt/A; PHI 0d, REI 4h. Apply preventatively in a minimum of 20 gallons of water/A.

Bacterial Blight of Parsnip (Pseudomonas marginalis)

Causes browning through the interior of the root. Practice at least a 2-year rotation.

Root and Crown Rot (Rhizoctonia solani)

Symptoms include dieback of foliage and brown sunken lesions on crowns. The pathogen has a wide host range, making crop rotation as a disease management tactic unsuccessful. Problems with this disease are more severe in organic soils and whenever undecomposed crop residue is present. Avoid crops such as alfalfa and legume cover crops which can increase disease risk. Wide spacing, weed control, and clean cultivation help reduce field infection by allowing soil to dry quickly. Avoid harvesting late in the season. 

FRAC Group 11:

• azoxystrobin (Quadris F): 0.4 to 0.8 fl oz/1000 row ft; PHI 0d, REI 4h. 

FRAC Group BM02:

• Bacillus amyloliquefaciens strain F727 (Stargus^OG): 1.0 to 4.0 qt/A; PHI 0d, REI 4h. Apply preventatively. 
• Bacillus subtilis Strain QST 713 (Minuet^OG): 6.0 to 12.0 oz/A; PHI 0d, REI 4h. Soil-applied. 

Itersonilia Canker or Sore Head  (Itersonilia perplexans)

Occurs on parsnip only. Dark, sunken cankers form primarily on the crown and shoulders. Plant on raised beds in well-drained soil. The varieties 'Gladiator' and 'Andover' are somewhat resistant. Rotate parsnip with non-susceptible hosts and control wild Apiaceae plant hosts. Start with certified disease-free seed. Protect roots by covering crowns and exposed upper roots with soil. Deep plow plant residue to reduce soilborne inoculum. Rarely occurs on young plants. Monitor fields near maturity and harvest affected fields early. Fungicide sprays are not effective.

White Mold (Sclerotinia sclerotiorum)

Fluffy white mycelium and black sclerotia distinguish this disease from other crown and root rots of carrots. The sclerotia can survive for many years on the soil. Rotate with small grains. Handle carrots carefully at harvest and washing. Use a postharvest sanitizer and change wash water frequently to reduce spread of pathogens. Clean and disinfect storage containers and harvesting equipment between batches. Cool carrots quickly to remove field heat. Inspect and dispose of infested carrots. Maintain storage and shipping temperatures of 32°F and 95% relative humidity.

FRAC Group 1:

• thiabendazole (Mertect 340F): 41.0 fl oz/100 gal; REI 12h. Dip carrots before storage. 

FRAC Group 3:

• fluopyram + difenoconazole (Luna Flex): 11.0 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7. Carrot only. Do not make more than 2 sequential applications before rotation with non- Group 3 or 7 fungicide. 

FRAC Group 7:

• fluopyram + difenoconazole (Luna Flex): 11.0 to 13.6 fl oz/A; PHI 7d, REI 12h, Groups 3 & 7. Carrot only. Do not make more than 2 sequential applications before rotation with non-Group 3 or 7 fungicide. 
• penthiopyrad (Fontelis): 16.0 to 30.0 fl oz/A; PHI 0d, REI 12h.

FRAC Group 29:

• fluazinam (Omega 500F): 16.0 fl oz/A; PHI 7d, REI 12h.

FRAC Group BM02:

• Ulocladium oudemansii (U3 strain) (BotryStop WP^OG): 2.0 to 4.0 lb/A; PHI 0d, REI 4h. Carrot only. Begin application when conditions are conducive to disease development. 

FRAC Group P04:

• laminarin (Vacciplant): 14.0 to 22.0 fl oz/A; PHI 0d, REI 4h. Carrot only. 

Aster Yellows (‘Candidatus Phytoplasma asteris’)

Aster yellows disease affects a wide range of crops, ornamentals, and weeds. The disease is caused by a phytoplasma, a wall-less bacterium that is incapable of living outside of its host plant or its vector, the aster leafhopper. The older foliage of affected carrots may turn yellow and/or reddish; newer leaves may be stunted and bushy. Taproots may be thin, stunted and/or distorted, and covered with numerous secondary roots (“hairy root”). 

Do not plant carrots or other sensitive crops in fields with a history of this disease. Remove infected plants and destroy crop residues immediately after harvest. Manage weeds, especially those in the Asteraceae family, and control leafhoppers. See the Carrot and Parsnip insect control section for information on aster leafhoppers.

Root-knot Nematode (Meloidogyne spp.)

Root-knot nematode is extremely damaging to carrots and parsnips, even at low population densities. Stunted, unthrifty foliage is often the first symptom of nematode damage on carrots and parsnips. Taproots often produce multiple forks and abundant fine feeder roots with small galls.

Monitor soils for nematode populations. Rotate with non-hosts such as cereals. Practice soil solarization or field fumigation in the fall. See Soil Fumigation Outdoors.

FRAC Group BM02:

• Purpureocillium lilacinum strain 251 (MeloCon^OG, LC and WG): 4 to 9 lb/A (preplant to soil), 2 to 4 lb/A (at planting), 0.5 lb/5 gal (drench to transplants) ; PHI 0d, REI 4h.