Sugar Beet (Beta vulgaris)-Cercospora Leaf Spot

By J. Gallian and C. M. Ocamb

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, especially under sprinkler irrigation. Other crop hosts include red beet, mangel, spinach, and Swiss chard; weedy hosts include redroot pigweed, lambsquarter, mallow, and bindweed. No resistant cultivars have been adapted for the Pacific Northwest. High humidity or free moisture and high temperatures (77°F to 95°F days, nights above 60°F) favor infection. Under humid conditions, conidia form on infected crop residue and are carried by wind or rain to host leaves. Spore production is optimal at 68°F to 79°F and 90% to 100% relative humidity. Disease can develop and spread, though more slowly, under a wider range of conditions.

Symptoms Numerous circular spots about 0.12 inch in diameter with tan to gray centers and dark brown to reddish purple-brown borders appear on leaves. The disease begins on older leaves but also appears on younger leaves as it progresses. In humid weather, spots may have a gray to steel-blue fuzzy appearance as spores are produced. Petioles also are affected. If spots are numerous, the entire leaf tends to wither and die prematurely, resulting in defoliation that reduces root growth and yield.

Cultural control

  • Plant at least 300 ft 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, reduce planting density.
  • Irrigate so plants dry by night.

Chemical control Sprays usually are not required if crops are rotated. Early disease detection and monitoring is essential to prevent economic loss. It is recommended that the field be sprayed when disease averages 0.5% infection (about 12 spots per leaf). Economic loss occurs if leaf spots cover at least 3% of the foliage by harvest (about 80 spots per leaf). To minimize fungicide resistance, rotate fungicides, apply them only as needed, and follow cultural control recommendations.

  • Copper products are registered for control of Cercospora leaf spot but tests in Midwestern sugar beet production have demonstrated little benefit from copper sprays.
    • Champ Formula 2 at 1.33 to 3.33 pints/A. 48-hr reentry.
    • C-O-C-S WDG at 2 to 2.5 lb/A in at least 25 gal water/A (ground) or 5 gal water/A (air). 48-hr reentry.
    • Copper-Count-N at 0.33 to 0.75 gal/A. Oregon only. 48-hr reentry
    • 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
    • Kocide 2000 at 1.5 to 3.74 lb/A on 10- to 14-day intervals. 48-hr reentry.
  • Demethylation-inhibiting (DMI) Fungicides (Group 3) are labeled for use. Do not make more than one (1) application before alternating to a labeled fungicide with a different mode of action.
    • Eminent 125 SL at 13 fl oz/A. Do not apply within 14 days of harvest. 12-hr reentry.
    • Inspire XT at 7 fl oz/A on 10- to 21-day intervals. Preharvest interval is 21 days. 12-hr reentry.
    • Proline 480 SC at 4.3 to 5.7 fl oz/A on 14- to 21-day intervals. Preharvest interval is 7 days. 12-hr reentry.
    • Tilt at 4 fl oz/A on 10- to 14-day intervals. Preharvest interval is 21 days. 12-hr reentry.
    • Topaz (Group 3) at 4 fl oz/A on 10- to 14-day intervals. Preharvest interval is 21 days. 12-hr reentry.
  • JMS Stylet Oil at 3 to 6 quarts/100 gal water. Do not apply sulfur for 21 days after applying oil. 4-hr reentry.
  • Mancozeb formulations are labeled.
    • Dithane DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops only. Washington and Oregon only (SLN WA-020028, SLN OR-020030). 24-hr reentry.
    • Dithane F45 Rainshield at 1.5 quarts/A on 7- to 10-day intervals can be used on seed crops only. Oregon only (SLN OR-090016). No portion of treated seed crop may be used or distributed for food or feed for 1 year (365 days) after the last application. 24-hr reentry.
    • ManKocide at 2.5 to 4.3 lb/A on 10-day intervals. Do not apply within 14 days of harvest. 48-hr reentry.
    • Manzate 75 DF at 1.5 to 2 lb/A. Do not apply within 14 days of harvest. Do not feed treated sugar beet tops to livestock. 24-hr reentry.
    • Penncozeb 75 DF at 1.5 to 2 lb/A. Do not apply within 14 days of harvest. 24-hr reentry.
    • Roper DF Rainshield at 2 lb/A on 7- to 10-day intervals can be used on seed crops only. Oregon only (SLN OR-130003). 24-hr reentry.
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Gem at 6 to 7 oz/A. Do not apply within 21 days of harvest. 12-hr reentry.
    • Headline at 9 to 12 fl oz/A. Preharvest interval is 7 days. 12-hr reentry.
    • Quadris Flowable at 9 to 15.5 fl oz/A. May be applied the day of harvest. 4-hr reentry.
  • Super Tin 80 WP at 2.5 to 5 oz/A by aircraft or closed-cab ground sprayer only. Do not use within 21 days of harvest. Do not graze or feed beet tops to livestock. 48-hr reentry. Restricted-use pesticide.
  • Topsin M WSB at 0.5 lb to 1/A. Do not apply more than once per season. Do not use alone; another non-benzimidazole fungicide should be used with Topsin M WSB for disease resistance management. Do not apply within 21 days of harvest. 24-hr reentry.
  • Trilogy at 0.5% to 1%. 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. Poor control as a stand-alone product. 4-hr reentry. O
  • Vertisan at 10 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 7 days; 0 days for forage and hay. 12-hr reentry.
  • Premixes of Group 7 + 11 fungicides are available for use. Do not make more than three (3) applications per season.
    • Priaxor Xemium Brand at 4 to 8 fl oz/A. Preharvest interval is 7 days. 12-hr reentry.

Biological control

  • LifeGard WG (Group P6) at 1 to 4.5 oz/100 gal on 7- to 14-day intervals for activating plant resistance. Use in rotation with fungicides labeled for use. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O

Reference Whitney, E.D., and Duffus, J.E. 1986. Compendium of Beet Diseases and Insects. St. Paul, MN: APS Press.