Damping-off is caused by a number of important vegetable pathogens and is very common during transplant production and early-spring. 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). 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. Overwatering, or having prolonged wet soils increase chances for Phytophthora and Pythium development. How do you know if your transplant trays are too wet? Simply pick one up. If it feels ‘heavy’ then you are overwatering and/or your soiless mix is too heavy and you need to improve its drainage by working more perlite and/or vermiculite into it when you make it. 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 Terraclor or OLF (PCNB, 14), iprodione (FRAC code 2), and Quadris (azoxystrobin, 11) helps control damping-off caused by Rhizoctonia. Ranman (cyazofamid, 21) and Previcur Flex (propamocarb HCL, 28) now have labels for use in the transplant water as well as via drip for pythium control. In addition, Presidio (fluopicolide, 43) and Orondis Gold (OXTP + mefenoxam, 49 +4) are labeled for use in drip irrigation. Please see labels for restrictions and crop uses. It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to properly apply. Always refer to the fungicide label for crop use, pathogens controlled and application rates. For information on controlling damping-off in transplant production please see specific crop section as well as Table E-14 on pages E52-E53 in the 2016-2017 Mid-Altantic Commercial Vegetable Production Guide for conventional and organic products labeled for greenhouse use.