Alternaria Leaf Spot (Alternaria spp.)
Symptoms include round, brown to gray lesions, sometimes with black, concentric rings, dark borders, and yellow haloes. The centers of the lesions may drop out over time, producing a “shot-hole” appearance. Severe infection may lead to defoliation. Alternaria leaf spot fungi do not affect radish roots but can reduce root yields if severe and will reduce the value of fresh-packed plants that retain the foliage. Buy certified disease-free seed or hot-water treat seed. Control brassica weeds and plow under crop debris in the fall. Rotate with non-brassica crops.
FRAC Group 7:
- penthiopyrad (Fontelis): 14 to 30 fl oz/A; PHI 0d, REI 12h.
FRAC Group 9:
- cyprodinil + fludioxonil (Switch 6.25 WG): 11 to 14 oz/A; PHI 7d, REI 12h, Groups 9 & 12.
FRAC Group 11:
- azoxystrobin (Abound F aka Quadris F): 6 to 20 fl oz/A; PHI 0d, REI 4h. Do not rotate with other Group 11 fungicides.
- pyraclostrobin (Cabrio EG): 8 to 12 oz/A; PHI 0d, REI 12h. 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.
FRAC Group BM02:
- Bacillus amyloliquefaciens strain D747 (Double Nickel 55OG): 0.25 to 3 lb/A (foliar); PHI 0d, REI 4h.
- Bacillus subtilis Strain QST 713 (Serenade MaxOG): 1 to 3 lb/A; PHI 0d, REI 4h. Begin applications soon after emergence and when conditions favor disease. Apply in sufficient water to provide thorough coverage.
Downy Mildew (Hyaloperonospora brassicae)
This disease occurs worldwide, affects most brassicas, and is most important at the seedling stage. Cool, humid weather is conducive to disease development. Foliar symptoms include yellow, angular spots on upper leaf surfaces and grayish-white, fuzzy sporulation on the undersides. Leaves eventually turn brown. The pathogen 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. Plant in well-drained soil and implement good cultural practices to facilitate air circulation. Plant resistant or tolerant cultivars.
FRAC Group M01:
- copper oxychloride + copper hydroxide (Badge X2OG): 1 to 2.25 lb/A; PHI 0d, REI 48h. Begin application when disease first appears or when conditions favor disease.
Seed Decay
Purchase treated seed. Do not use treated seed for food, feed, or oil purposes.
FRAC Group 4:
- mefenoxam (Apron XL SL): 0.085 to 0.64 fl oz/100 lb seed; REI 48h.
- mefenoxam (Ridomil Gold SL): 1 to 2 pt/A; REI 48h. Pre-plant incorporated or soil spray broadcast or band.
FRAC Group 11:
- azoxystrobin (Abound F aka Quadris F): 0.4 to 0.8 fl oz/1000 row feet; PHI 0d, REI 4h.
FRAC Group 12:
- fludioxonil (Maxim 4FS): 0.08 to 0.16 oz/100 lb seed; REI 12h. For protection against seedborne and soilborne fungi. Does not control Pythium or Phytophthora.
FRAC Group 43:
- fluopicolide (V-10161 4SC, aka Presidio): 3 to 4.0 fl oz/A; PHI 7d, REI 12h. For Pythium control. Apply as banded spray. Application at seeding may help control downy mildew.
FRAC Group BM02:
- Bacillus amyloliquefaciens strain D747 (Double Nickel 55OG): 0.25 to 3 lb/A (foliar); PHI 0d, REI 4h.
White Rust (Albugo candida and A. cruciferarum)
Yield reductions caused by white rust are rare, but quality is reduced by the prominent, raised white spore masses on the undersides of leaves. On radish, white rust can also infect flower shoots and cause root swellings. Use resistant cultivars where available and rotate to non-brassica crops where the disease is common. Proper fertility levels, especially of phosphorus and potassium, have been reported to reduce disease.
FRAC Group 11:
- azoxystrobin (Abound F aka Quadris F): 6 to 20 fl oz/A; PHI 0d, REI 4h. Do not make more than 1 foliar application before alternating with a non-Group 11 fungicide.
- pyraclostrobin (Cabrio EG): 8 to 16 oz/A; PHI 0d, REI 12h. Do not rotate with other Group 11 fungicides.
FRAC Group M01:
- copper oxychloride + copper hydroxide (Badge X2OG): 1 to 2.25 lb/A; PHI 0d, REI 48h. Begin application when disease first appears or when conditions favor disease.