With the current cold and wet spring conditions, the risk of damping-off caused by pythium and phytophthora species is high. If/when the conditions shift to warmer and drier, fusarium and rhizoctonia species will be the primary causes of damping-off.
Damping-off can occur pre or post-emergence and can cause serious losses and reductions in stands of direct-seeded vegetable crops including: cucumbers, lima and snap beans, sweet corn, etc. In order to manage damping-off, the causal pathogen needs to be identified, this can be difficult though, as the symptoms are often similar between the pathogens.
Generally, pythium kills seedling pre-emergence, while rhizoctonia and fusarium kill seedlings post-emergence. Pythium and Phytophthora symptoms are a soft, mushy rot with dark brown to black lesions pre-emergence or water-soaked lesions that start on the roots and spread above the soil line on the stem, eventually causing wilt, post-emergence.
Rhizoctoniasymptoms are tan to reddish-brown lesions pre-emergence and reddish-brown to black lesions on the roots and stem causing wilt post-emergence. Fusarium causes dark brown to black lesions on hypocotyls pre-emergence and similar colored lesions on roots and near the soil line post-emergence. Lab identification may be required to accurately identify the pathogen. Proactive approaches such as seed treatments and soil-applied fungicides applied at planting are the best ways to manage damping-off.
The biology of the pathogens play a large role in which fungicides will properly manage the disease. Fusarium and rhizoctonia are true fungi and will be best controlled with azoxystrobin (Quadris), thiram, fludioxonil (Celest), or quintozene/PCNB (Terraclor). Pythium and phytophthora are oomycetes and are best controlled with metalaxyl (MetaStar/Allegiance), mefanoxam (Ridomil/Apron), penthiopyrad (Fontelis) and propamocarb (Previcur Flex) for pythium only. Pre-mix seed treatments can have activity on all damping-off pathogens, some examples are fludioxanil + metalaxyl (Maxim XL) and mefanoxam + azoxystrobin (Uniform).
There are also a number of options for organic growers. Streptomyces griseoviridis (Mycostop),Streptomyces lydicus (Actinovate), Trichoderma harzianum(BioEnsure, PlantShiled, RootShield), Trichoderma virens(SoilGard), Bacillus subtillus (Companion), and Bacillus amyloliquefaciens(Double Nickel) are all biological options that compete for root space with the damping-off pathogens to reduce disease.
An extract of Reynoutria sachalinensis(Regalia) is a biopesticide that induces plant defense mechanisms and can be used for management of damping-off, as well. Read labels carefully for application information, crop use, and pathogens controlled.
– Jake Jones, Extension, University of Delaware Agriculture Agent, Kent County