By O. Neher and C. M. Ocamb
Cause The soilborne fungi or fungus-like microorganisms, Pythium spp., Rhizoctonia solani, and Aphanomyces cochlioides, may attack before, during, and after germination. In the Pacific Northwest, Pythium spp. are the major cause of pre- and post-emergence damping-off of young seedlings. Pythium ultimum is the primary species and is favored by cool soil temperatures. Rhizoctonia solani is more often associated with post-emergence damping-off of older seedlings and can be a problem when the crop is replanted due to loss by frost or other causes and soil temperatures are warm; it is favored by warmer soil temperatures. Aphanomyces cochlioides causes post-emergence damping off and is favored by wet soils. These fungi can survive several years in soil and can infect other plant species including beans and other legumes, including some weed species.
Symptoms Seeds either do not emerge, or emerged seedlings often develop blackened stems and wilt. Very few infected seedlings survive.
Cultural control
- Encourage rapid emergence by managing planting depth (shallow), timing, and soil moisture. Work soil at moisture conditions that reduce soil compaction.
- Rotate beet crops with grass and grain.
- Placing phosphate fertilizer in a band one inch below seed often prevents damping-off.
- If the stand is lost, replant ideally in dry, warm weather, which is more favorable for germination.
Chemical control
- Seed treatments.
- Allegiance-(Group 4) FL at 0.75 fl oz/100 lb seed plus a dye for Pythium spp. 24-hr reentry.
- Apron XL (Group 4) at 0.085 to 0.64 fl oz/100 lb seed plus a dye for Pythium spp. 48-hr reentry.
- Captan 4F (Group M4) at 6 fl oz/100 lb seed plus a dye.
- Maxim 4FS (Group 12) at 0.08 to 0.16 fl oz/100 lb seed plus a dye. Controls Fusarium and Rhizoctonia spp. 12-hr reentry.
- Tachigaren 70 WP (Group 32) at 45 g or less/100,000 seeds plus a dye for Aphanomyces and Pythium spp. Higher rates may be phytotoxic. See label for reentry restrictions.
- 42-S Thiram (Group M3) at 8 fl oz/100 lb seed plus a dye. 24-hr reentry.
- Soil-applied fungicide.
- MetaStar 4S (Group 4) at 2 to 4 pints/A as a preplant or at planting treatment. Controls Pythium spp. 48-hr reentry.
- Quadris Flowable (Group 11) at 0.4 to 0.8 fl oz/1000 row feet applied in a 7-inches or less band either in-furrow at planting or as a directed spray at cultivation.
- Ridomil Gold SL (Group 4) at 1 to 2 pints/A applied preplant and incorporated or applied over the row after planting for Pythium control. 48-hr reentry.
Biological control
- SoilGard at 0.5 to 10 lb/A at 4-week intervals will suppress Pythium and Rhizoctonia. See label for specific application types and timings. Can be applied on the day of harvest. 4-hr reentry. O