Interaction Between Powdery Mildew and N and K Fertility in Begonia

Abstract

Nine fertility treatments, consisting of a 3 × 3 factorial arrangement of three N rates (30, 120, 240 μg·ml–1) and three K rates (30, 120, 240 μg·ml–1), were applied by constant liquid feed to cuttings of Hiemalis begonia `Hilda' grown in 15-cm plastic pots containing 7.5 peat: 2.5 perlite medium. Prior to transplanting, one-half of the plants were naturally inoculated with Erysiphe cichoracearum to induce powdery mildew infection; while the remaining plants received weekly application of Bayleton (Triadimefon). Shoot growth in fungicide-treated plants increased with increasing rates of both N and K, with highest dry matter production (≈8.0 g/plant) with either 120N–240K or 240N–120K. Disease development in plants treated with fungicide was slight, averaging < 7% of the total leaf surface area infected with mildew, irrespective of N and K rates. Shoot dry weights in inoculated plants were markedly repressed, averaging 3.1 g/plant, as disease occurrence was extensive in all treatments. Significant interactions between N and K fertility affected mildew development in inoculated plants. At the high rate of N, K nutrition had little effect on mildew rating, whereas at 30N and 120N, mildew counts decreased with increasing K rate up to 120 K.