Cause Cercospora beticola, a fungus perpetuated in beet refuse. It can be spread on seed produced in regions where the disease is severe. It is not a major disease in the Pacific Northwest but occasionally causes serious leaf spot. Other hosts include sugar beet, mangel, spinach, and Swiss chard. No resistant varieties of table beet are known.
The disease is favored by high humidity or free moisture and high temperatures (77°F to 95°F). Under humid conditions, conidia form on infected crop residues and are carried by wind or rain to host leaves.
Symptoms Numerous small circular spots about 0.12 inch in diameter appear on leaves. These have definite margins, often deeper in color (dark brown to reddish purple) than surrounding tissue. Centers turn brown and later gray as spores are produced. Petioles also are affected. When spots are numerous, the entire leaf tends to wither and die prematurely, reducing root growth and yield.
Cultural control
- Plant at least 100 yd from last season's plantings.
- Do not replant on the same land for 3 years.
- Plow deeply to completely bury infected refuse.
- If leaf spot is serious, density of planting may be reduced.
- Apply irrigation so plants are not wet at night.
Chemical control Sprays are not required if a proper rotation is followed.
- Copper formulations (Group M1) are registered.
- Badge SC at 0.75 to 4 pints/A on 10- to 14-day intervals. Preharvest interval is 0 days. 48-hr reentry.
- C-O-C-S WDG at 2 to 2.5 lb/A in a minimum of 25 gal/A water (ground) or 3 gal/A water (air). 48-hr reentry.
- Champ WG at 2.02 lb/A on 10- to 14-day intervals. 48-hr reentry. O
- Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
- Cuprofix Ultra 40 Disperss at 1.25 to 3 lb/A on 10- to 14-day intervals. 48-hr reentry.
- Kocide 2000 at 1.5 to 3.74 lb/A or Kocide 3000 at 0.75 to 2 lb/A on 10- to 14-day intervals. 48-hr reentry. O
- Previsto at 1 to 2 quarts/A on 10- to 14-day intervals. 48-hr reentry. O
- Demethylation-inhibiting (DMI) fungicides (Group 3) are labeled for use.
- Cevya at 3 to 5 fl oz/A on minimum interval of 7 days. Preharvest interval is 7 days. 12-hr reentry.
- Tilt at 3 to 4 fl oz/A on 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
- Topaz at 3 to 4 fl oz/A on 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
- Fontelis (Group 7) at 16 to 30 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action (non-Group 7). Preharvest interval is 0 days. 12-hr reentry.
- Mancozeb formulations (Group M3) are labeled.
- Dithane F45 Rainshield at 1.5 quart/A on 7- to 10-day intervals can be used on seed crops only. Washington and Oregon only (SLN WA-220008, SLN OR-090016). 24-hr reentry.
- Roper DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops in Oregon (SLN OR-130003) and Washington (SLN WA-1300003) only. 24-hr reentry.
- Merivon Xemium (Group 7 + 11) at 5.5 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) applications before alternating to a fungicide in different FRAC groups (non-Group 7 and non-Group 11). Preharvest interval is 7 days. 12-hr reentry.
- Miravis Prime (Group 7 + 12) at 6.8 fl oz/A on 7- to 10-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 7 days. 12-hr reentry.
- Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of any Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
- Cabrio EG at 8 to 12 oz/A on 7- to 14-day intervals. Preharvest interval is 0 day. 12-hr reentry.
- Quadris Flowable at 9 to 15.5 fl oz/A on 7- to 14-day intervals. May be applied the day of harvest. 4-hr reentry.
- Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. 4-hr reentry. O
Biological control
- LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
Reference Harveson, R.M., Hanson, L.E., and Hein, G.L. 2009. Compendium of Beet Diseases and Pests, 2nd Ed. St. Paul, MN: APS Press.