Damping-off is caused by a number of important vegetable pathogens and is very common at seeding and transplanting in spring and fall. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off) or soon after transplanting. Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia, and Fusarium spp.
It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to properly apply.
Although all four pathogens are associated with damping-off, the conditions which favor their development are very different. In general, Phytophthora and Pythium are more likely to cause damping-off in cool, wet soils. While, Rhizoctonia and Fusarium are more likely to cause damping-off under warmer, drier conditions. In general, Pythium tends to kill seedlings before they emerge whereas Rhizoctonia and Fusarium tend to kill seedlings after emergence. There are exceptions to the rules in some cases, but none the less, all damping-off pathogens can cause serious losses if not controlled properly.
Control of damping-off depends on a number of factors. First is recognizing the conditions which may be leading to the problem (i.e., weather/greenhouse growing conditions) and second, identifying the pathogen causing the problem. Why is this so important? The fungicides applied to prevent or control damping-off are specific in the pathogens they control.
Fungicides used to control Pythium or Phytophthora won’t control the other damping-off pathogens. Why is this? The biology of the fungus and the mode of action of the fungicide dictates efficacy. For example, Ridomil Gold and Ultra Flourish (mefenoxam, FRAC code 4), MetaStar (metalaxyl,4) and Previcur Flex (propamocarb, 28) helps control the ‘water molds’ (Pythium and Phytophthora spp.) where azoxystrobin (FRAC code 11) helps control damping-off caused by Rhizoctonia. Ranman (cyazofamid, 21) can be applied as a directed spray (drench) for Pythium and Phytophthora control. Previcur Flex (propamocarb HCL, 28) has a label for use in transplant water or as a directed spray in some crops for Pythium control. Presidio (fluopicolide, 43) is labeled for use in drip irrigation or can be applied as a drench for Pythium and Phytophthora control. Please see labels for restrictions and uses. Switch (cyprodinil + fludioxonil, 9 + 12) has a herb and leafy green label which includes Fusarium control in cilantro and parsley. It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to apply. Additionally, it is important that these fungicides be applied preventatively and using a method (i.e., heavy directed spray or drench) that gets the fungicide where it needs to be in the root zone. Always refer to the fungicide label for crop use, pathogens controlled, and application rates.
