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, days to harvest (dh), REI, and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 28 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.
Alternaria leaf spot
Alternaria leaf spot does not affect the root but will reduce the value of fresh-packed plants that retain the foliage. Buy certified disease-free seed or hot-water treat seed. Reduce cruciferous weeds and plow under crop debris in the fall. Rotate with non-cruciferous crops.
azoxystrobin (Quadris): 6.0 to 15.5 fl oz/A. (0 dh, REI 4h, Group 11). Do not rotate with other strobilurin (Group 11) fungicides.
penthiopyrad (Fontelis): 16.0 to 30.0 fl oz/A. (0 dh, REI 12h), Group 7).
cyprodinil plus fludioxonil (Switch 6.25 WG): 11.0 to 14.0 oz/A. (7 dh, REI 12h, Groups 9 & 12).
pyraclostrobin (Cabrio EG): 8 to 12 oz/A. (0 dh, REI 12h, Group 11). Do not alternate with Group 11 fungicides such as Quadris.
Downy Mildew (Hyaloperonospora parasitica)
This disease occurs worldwide, affects most crucifers, and is most important at the seedling stage. It is an important pathogen on radish because it can infect the fleshy root, causing external black patches, lesions on the root shoulder, and internal grey or black flecking and streaking. The root surface is scarred, prone to cracking or splitting, and unmarketable. Manage Downy mildew on transplants by improving air circulation and irrigating early in the day so plants can dry quickly. Plant resistant or tolerant cultivars.
Buy treated seed. Do not use treated seed for food, feed or oil purposes.
azoxystrobin (Quadris): 0.40 to 0.80 fl oz/1000 row feet. (0 dh, REI 4h, Group 11).
fludioxonil (Maxim 4FS): 0.08 to 0.16 oz/100 lb seed. (REI 12h, Group 12). For protection against seed-borne and soil-borne fungi. Does not control Pythium or Phytophthora.
mefenoxam (Apron XL): 0.085 to 0.64 fl oz/100 lb seed. (REI 48h, Group 4).
mefenoxam (Ridomil Gold SL): 1.0 to 2.0 pt/A. (REI 48h, Group 4). Pre-plant incorporated or soil spray broadcast or band).
thiram (Thiram 42 S): 8.0 lb/100 lb seed. (REI 12h, Group M3).
White Rust, White blister (Albugo candida)
Yield reductions are rare but quality is reduced by the prominent signs of the pathogen. On radish, white rust can also infect flower shoots and cause root swellings. Use resistant cultivars where available and rotate to non-hosts where the disease is common. Proper fertility levels, especially of phosphorous and potassium, have been reported to reduce disease.
azoxystrobin (Quadris): 6.0 to 15.5 fl oz/A. (0 dh, REI 4h, Group 11). Do not make more than one foliar application of Quadris before alternating with a non-group 11 fungicide.
pyraclostrobin (Cabrio EG): 8.0 to 16.0 oz/A. (0 dh, REI 12h, Group 11). Do not rotate with other Group 11 fungicides.