Disease Control

NOTE: For the disease control products listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 25 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

The symbol OG indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more details.

Leaf Blight (Cercospora, Septoria, or Alternaria)

Use certified, disease-free seed or treat seed with hot water or fungicides. Rotate fields. 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 where available. Apply fungicides based upon a disease forecasting system.

azoxystrobin plus chlorothalonil (Quadris Opti): 2.4 pt/A; PHI 0d, REI 12h, Groups 11 & M5. See label for tank mix precautions.

azoxystrobin plus propiconazole (Quilt): 14.0 fl oz/A; PHI 14d, REI 12h, Groups 11 & 3. 

boscalid (Endura): 4.5 oz/A; PHI 0d, REI 12h, Group 7. For Alternaria only.

chlorothalonil (Bravo Weather Stik): 1.5 to 2.0 pt/A; PHI 0d, REI 12h, Group M5.

copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h, Group M1. Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette. 

cyprodinil plus fludioxonil (Switch 6.25 WG): 11.0 to 14.0 oz/A; PHI 7d, REI 12h, Groups 9 & 12.   

fluazinam (Omega 500F): 1.0 pt/A; PHI 7d, REI 48h, Group 29.

iprodione (Rovral 4F): 1.0 to 2.0 pt/A; PHI 0d, REI 24h, Group 2.

penthiopyrad (Fontelis): 16.0 to 30.0 fl oz/A; PHI 0d, REI 12h), Group 7.

polyoxin D (OSO 5%SC): 3.75 to 13.0 fl oz/A; PHI 0d, REI 4h, Group 19.

propiconazole (Tilt): 4 fl oz/A; PHI 14d, REI 12h, Group 3.

pyraclostrobin plus 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): 2.0 to 3.0 oz/A; PHI 7d, REI 12h, Group 11. Do not alternate with other Group 11 fungicides.

Crater Rot (Rhizoctonia carotae)

Crater rot caused by Rhizoctonia carotae is a post-harvest disease of carrot that results from prolonged cold storage (greater than 30 days). The pathogen is soilborne and initial infection occurs before harvest. Late harvested carrots may have higher amounts of infection. The fungus then develops in cold storage (4 to 6°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 reduce disease and prevent dehydration. Removal of carrots from cold storage early can prevent losses.

Parsnip Blight (Pseudomonas marginalis)

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

Root and Crown Rot (Rhizoctonia)

A 2-year rotation is recommended to prevent buildup of disease-causing organisms. Avoid crops such as alfalfa and legume cover crops which can increase disease risk. Avoid cultivating late in the season. Maintain storage conditions at 50°F.

azoxystrobin (Quadris): See label for in-furrow and drench rates; PHI 0d, REI 4h, Group 11.

Bacillus amyloliquefaciens F727 (StargusOG): 2 to 4 qt/A; PHI 0d, REI 4h, Group 44. Apply preventatively in a minimum of 50 gallons of water/A.

polyoxin D (OSO 5%SC): 3.75 to 13.0 fl oz/A; PHI 0d, REI 4h, Group 19.

Trichoderma asperellum, T. gamsii (Bio-tamOG): See label for in-furrow, drench, and broadcast rates; REI 1h, Group NC.

Sore Head (Itersonilia perplexans)

Occurs on parsnip only. Plant on raised beds in well-drained soil. The variety Model is 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.

Storage Rots (White Mold (Sclerotinia sclerotiorum) and Black Mold (Thielaviopsis basicola)

Handle carrots carefully at harvest and washing.  Use chlorine 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.

penthiopyrad (Fontelis): 16.0 to 30.0 fl oz/A; PHI 0d, REI 12h), Group 7.

thiabendazole (Mertect 340F):  41 fl oz/100 gal; REI 12h, Group 1.

fluazinam (Omega 500F): 1.0 pt/A; PHI 7d, REI 48h, Group 29.

Xanthomonas Leaf Blight (Xanthomonas campestris pv. carotae)

Xanthomonas leaf blight is easily confused with Alternaria leaf blight, and they can occur at the same time. "Waltham Hi-Color" and "Danvers" have some tolerance to Xanthomonas. Start with certified disease-free seed or treat seed with hot water. Rotate with non-susceptible crops on a 2- to 3-year cycle. Copper sprays partially reduce disease severity only if applied early in the crop cycle and repeated at 7- to 10-day intervals.

copper hydroxide (Kocide 3000): 0.75 to 1.5 lb/A; PHI 0d, REI 48h, Group M1. Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette. 

Aster Yellows

Remove inoculum sources by controlling weeds (alternate hosts). Avoid fields near pastures or river banks that harbor susceptible vegetation. Destroy residues from susceptible crops immediately after harvest. Control the six-spotted leafhopper that carries the mycoplasma (see Carrot and Parsnip, Insect Control).

Root-Knot Nematode (Meloidogyne)

Low densities of root knot nematodes before planting means susceptible crops will suffer damage. 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, page 89.