Evaluation of Fungicides to Control Pythium Root Rot of Geranium, 2025

Geranium ‘Black Velvet’ seeds were planted in 72-cell flats at the research greenhouses of the University of Connecticut. Seedlings with three to four true leaves were transplanted on 31 August into 4.5-in. pots into PRO-MIX BX potting mixture containing 1 g/liter of Pythium-infested millet. Sterilized millet was infested with Pythium ultimum (isolate 024P, originally from geranium) prior to use as inoculum. Each pot was fertilized with 1 g of Osmocote and received weekly applications of 20-20-20 liquid fertilizer. No fungicides or insecticides were applied as maintenance sprays. There were six pots per treatment arranged in a completely randomized design. Immediately after transplant, the plants were drenched with 120 ml of fungicide solution, which was sufficient to displace 10% water in each pot. A second drench application was made 7 days after treatment A on 7 September. The greenhouse was maintained between 15.5 to 29.5°C. The plants were rated for disease severity and phytotoxicity, and fresh weights of aboveground plant parts were recorded at the conclusion of the trial. Data were analyzed using an analysis of variance (ANOVA) with means separation preformed using Fisher's protected least significant difference (LSD) test using JMP software.