Efficacy of Fungicides and Biopesticides for Management of Phytophthora Crown and Root Rot of Gerber Daisy

Abstract

Several fungicides and biopesticides were evaluated for control of Phytophthora crown and root rot of Gerber daisy caused by P. cryptogea, a frequently encountered pathogen in greenhouse production. In greenhouse trials, biopesticides were applied 3 to 5 days before inoculation with P. cryptogea, while fungicides were applied at the time of inoculation. Efficacy of the treatments was assessed according to fresh plant top weights and root rot ratings at the end of experiments. Phosphite salt fungicides such as AgriFos, Aliette, Alude, Magellan and Vital sprayed to run off prior to inoculation were ineffective. Similarly, the strobulurins (Disarm, Heritage, and Insignia) as a drench and the biopesticides (Muscodor albus, Remedier, and Taegro) incorporated or as a drench failed to prevent root and crown rot and collapse of plants. Adorn as a drench at 2 fl oz/100 gal prevented Phytophthora crown and root rot in two of three trial years. Fenstop as a drench at 14 fl oz/100 gal or Orvego as a drench at rates of 22.5 to 34 fl oz/100 gal consistently controlled disease in three years of trials. Segway as a drench at 6 fl oz/100 gal varied in efficacy but in all trials, disease development was less than the non-treated, inoculated control. Because the effective fungicides are in different Fungicide Resistance Action Committee codes, growers have valuable rotation options for managing crown and root rot caused by P. cryptogea on Gerber daisy and avoiding pathogen resistance in the Phytophthora populations. Accepted for publication 18 February 2011. Published 12 May 2011.