Effects of AG3 phosphonate formulations on incidence and severity of Pythium damping-off of cucumber seedlings under growth room, microplot, and field conditions

Abstract

New formulations of phosphonates (AG3) were tested for their efficacy to control Pythium damping-off of cucumber seedlings in peat-based mix (P-mix), muck soil (Mu-soil), and sandy loam soil (SL-soil). Aqueous solutions of various phosphonate formulations (0.035%–0.280% active ingredient (a.i.), v/m) were added to pathogen-infested Pmix or SL- or Mu-soils as a preplanting amendment or postplanting drench treatments. In artificially infested P-mix, preplanting amendment with powder or liquid phosphonate formulation provided control of damping-off and disease suppression that increased with the concentration of phosphonate. Higher rates (0.140% or 0.280% a.i.) provided almost 100% disease control whereas lower rates (0.035% or 0.070% a.i.) had on average 34%–75% healthy plants compared with less than 5% in the control. AG3 liquid formulation as a preplanting treatment also provided effective control in naturally infested Mu-soil and artificially infested SL-soil. Postplanting drench with AG3 was equally effective in all three soil substrates. AG3 applied as an amendment 2 weeks prior to planting in Mu-soil was as effective as that added just prior to planting. Treatments made prior to 2 weeks were less effective. AG3 also provided effective control of Pythium damping-off of cucumber seedlings under microplot and field conditions. The amount and frequency of irrigation and rainfall can affect the disease suppression by AG3 phosphonate in the field.