Disease Control

NOTE:  For the products for disease control listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 22 and Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

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 (Quadris): 9.0-15.5 fl oz/A. (0 dh, REI 4h, Group 11). Do not alternate with other Group 11 fungicides.

chlorothalonil (Bravo Ultrex): 1.4 to 1.8 lb/A (0 dh, REI 12h, Group M5). Apply at the first sign of disease; repeat at 7- to 10- day intervals.

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

pyraclostrobin (Cabrio EG): 8 to 12 oz/A (0 dh, REI 12h, group 11). Apply at the first sign of disease and alternate with chlorothalonil after 7 to 14 days if necessary. Apply only three applications per season or 48 oz/A. Do not rotate with other strobilurins such as Quadris.

pyraclostrobin plus boscalid (Pristine): 8-10.5 oz/A. (0 dh, REI12h, Groups 11 & 7). Do not alternate with Quadris or Cabrio.

Xanthomonas Leaf Blight (Xanthomonas)

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 2-3 year cycle. Copper sprays partially reduce disease severity only if applied from early in the crop cycle and repeated at 7-10 day intervals.

basic copper sulfate (Basic Copper 50W HB): 0.5-2.0 lb/A. (0 dh, REI 48h, Group M1). Do not apply in a spray solution having a pH less than 6.5. Late applications may cause phytotoxicity.

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. Soil solarization or field fumigation in the fall. See Soil Fumigation on page 59.

Parsnip Blight (Pseudomonas marginalis)

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

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 Insect Management).

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.

Root and Crown Rot (Rhizoctonia)

A two-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.