Dexon controlled damping-off and root rot of zinnia seedlings caused by Pythium ultimum when used as a drench at 27 to 70 ppm in solution (or incorporated in the soil at the rate of 55 to 110 ppm). However, the drench at 70 ppm and soil preparation at 110 ppm controlled the disease for one month under the conditions of the tests reported here. More chemical was needed when incorporated with the soil (110 ppm = 6.2 oz per cubic yard) than when it was used as a drench (2.5 gal of 70 ppm solution per cubic foot = 0.9 oz per cubic yard). If soil is steamed or chemically fumigated, periodic drenches of 70 ppm at one-month intervals are suggested to prevent reinfection by Pythium root rot. Terrazole controlled Pythium damping-off and root rot when incorporated into the soil at the rate of about 55 ppm (3.5 oz per cubic yard). Terrazole is not yet available for use on ornamentals.

Dexon (p-dimethylaminobenzenediazo sodium sulfonate) is the registered trademark of Chemagro Corporation. Terrazole (5-ethoxy-3-trichloromethyl-1,2,4-thiadiazole) is the registered trademark of Olin Mathieson Chemical Corporation. Chrysanthemum rooted cuttings were donated for these tests by the California-Florida Plant Corporation, Fremont, California.