Effect of block co-polymer blended surfactants on substrate wettability and on relative phytotoxicity of impatiens and pansy

Abstract: Surfactant formulations consisting of proprietary blends containing sulfonic acid ester ethylene oxide/propylene oxide block copolymer blend (ACA3204-R and ACA3204-P); sulfonic acid ester ethylene oxide/propylene oxide block copolymer blend with polyethylene glycol addition (ACA3204-2a), and ethoxylated alkylphenol (ACA160) were tested for wettability of peat-based substrates and for relative phytotoxicity. Substrate incorporation rates used in this study were 116 mL m^-3 (a low recommended rate), 232 ml m^-3 (a moderate recommended rate), and 464 ml m^-3 (a supra-optimal rate). After a third wetting cycle, those substrates incorporated with ACA3204-R, ACA3204-P, or ACA160 at 232 ml m^-3 had higher wettability ratings than the Pro-Mix HP control (Premier Horticulture Inc., Quakertown, PA). There were no differences in shoot dry weight (SDW) or visual root health rating (VRHR) among treatment groups of impatiens (Impatiens walleriana) compared to the control For pansy (Viola × wittrockiana), Pro-Mix-HP control-grown plants had higher SDW (0.8632 g shoot^-1) than ACA3204-R at 464 mL·m^-3 (SDW = 0.6266 g shoot^-1) but SDWs for ACA3204-P, ACA3204-2a and ACA160 were similar to the control at all rates. Compared to the control, pansy VRHRs declined at 464 ml m^-3 for all surfactants except for ACA160. In general, higher rates of surfactant increased mean days to 50% germination (D_X; an inverse measure of germination rate) compared to distilled water control for pansy but this effect was less pronounced for impatiens. There appeared to be a stimulatory seedling effect on mean pansy root length for ACA3204-R and ACA3204-P (rates = 300-1200 ppm) and for ACA3204-2a (rates = 600-1200 ppm). In conclusion, surfactant formulations ACA3204-R, ACA3204-P, ACA3204-2a, and ACA160 were comparatively non-phytotoxic at moderate rates of substrate incorporation (mature plant growth) but laboratory seed germination was affected by low concentrations. ACA3204-R had similar wettability rating to that of ACA160 following the third wetting cycle. Further testing with additional plant species and substrates would aide in evaluating the usefulness of newer horticultural surfactants.