Control of Bacterial Wilt of Geranium with Phosphorous Acid.

Various bactericides were screened for efficacy in protecting geranium plants (Pelargonium hortorum) from Ralstonia solanacearum infection. Many of these bactericides were found to slow the disease progress; however, they were not able to protect the plants from infection and subsequent death. Potassium salts of phosphorous acid were found to be effective in protecting plants from infection when applied as a drench. The active portion of the potassium salts was found to be phosphorous acid (H3PO3). Phosphorous acid was found to inhibit in vitro growth of R. solanacearum. It is thought to be protecting plants from infection by acting as a bacteriostatic compound in the soil. The plants, however, are not protected from aboveground infection on wounded surfaces. Phosphorous acid drenches were shown to protect geranium plants from infection by either race 1 or 3 of R. solanacearum. Other phosphorous-containing products commonly used in the industry, such as phosphorus pentoxide (P2O5) and phosphoric acid (H3PO4), were not able to protect plants from bacterial wilt infection.