Lettuce (Lactuca sativa)-Damping-off

Cause Pythium ultimum or Rhizoctonia solani, fungus-like and fungal microorganisms that live in soil and attack seedlings of many different crops. As seedlings mature, they become resistant to attack. The disease can be a serious problem in cool, wet soils.

Symptoms Seedlings may be attacked before or after they emerge from the soil, resulting in gaps and uneven stands. Young plants suddenly wilt and topple over. Water-soaked lesions are apparent on stems at the soil line.

Cultural control

  • Delay planting until soil warms to increase seedling growth and emergence.
  • Mulch soil to increase soil temperature.
  • Plant shallowly to promote quick emergence and growth.

Chemical control

  • Treat seed with fungicide.
    • Allegiance-FL at 0.75 fl oz/100 lb seed plus a dye. To control Pythium spp. only. See label for reentry restrictions.
    • Apron XL at 0.085 to 0.64 fl oz/100 lb seed plus a dye. Controls Pythium only. See label for reentry restrictions.
    • Dynasty at 0.1 to 0.38 fl oz/100 lb seed plus a dye. 4-hr reentry.
    • Maxim 4FS at 0.08 to 0.16 fl oz/100 lb seed plus a dye. For control of pathogenic Fusarium and Rhizoctonia spp. See label for reentry restrictions.
    • 42-S Thiram at 8 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
  • Orondis Gold (Group 49 + 4) at 13.9 to 27.8 fl oz/A as an in-furrow, transplant water or banded soil application at planting. May be applied through drip after emergence. Preharvest interval is 7 days. 48-hr reentry.
  • Quadris Flowable at 0.4 to 0.8 oz/1,000 row feet applied in a 7-inch or less band either in-furrow at planting or as a directed spray at cultivation. 4-hr reentry.
  • Ridomil Gold SL at 1 to 2 pints/A if Pythium is a problem. Can apply as a surface application or in a 7-inch band according to label rates. May be incorporated to 2-inches deep. See restrictions when controlling downy mildew. 48-hr reentry.

Biological control Efficacy in the Pacific Northwest is unknown.

  • Cease at 4 to 8 quarts in 100 gal water applied to soil at 1 pint/square ft for each 3-inches of soil depth on a 21- to 28-day interval. For greenhouse plants only. 4-hr reentry. O
  • Double Nickel LC at 0.5 to 4.5 pints/A for soil application on 14- to 28-day intervals. Can be applied the day of harvest. 4-hr reentry. O
  • Prestop as a soil drench or incorporation into growing medium. 4-hr reentry. O
  • Rootshield Home and Garden at 1 to 3 Tbsp/gal water as a soil drench at planting. H O
  • Rootshield WP at 3 to 5 oz/100 gal water for greenhouse soil drench and field chemigation or at 16 to 32 oz/A as an in-furrow spray. 0-hr reentry. O
  • SoilGard 12G 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. O