Nitrogen Nutrition, But Not Potassium, Affects Powdery Mildew Development in Hiemalis Begonia

Abstract

For obligate parasites like Erysiphe cichoracearum, manipulation of nitrogen (N) and potassium (K) nutrition may provide an alternative control method for powdery mildew in greenhouse crops. Subsequently, Hiemalis begonias “Hilda” and “Renaissance” were grown in separate experiments with a factorial combination of three N (30, 120, 240 mg L⁻¹) and three K (30, 120, 240 mg L⁻¹) rates applied at each irrigation. One‐half the plants in each treatment were inoculated with E. cichoracearum, while the remaining plants were sprayed regularly with the fungicide triadimefon to prevent disease development. Plant growth and powdery mildew incidence in both cultivars were significantly influenced by N fertilization and pathogen inoculation, but relatively unaffected by K fertility. Shoot dry mass in both cultivars increased with increasing N rate up to 120 mg N/L, but decreased from pathogen inoculation. This latter response increased in magnitude with increasing N rate in “Hilda”, but not in “Renaissance”. Pathogen inoculation increased powdery mildew disease severity (PMDS) in both cultivars. Nitrogen fertilization had a positive effect on PMDS, primarily at the later production stages. Total disease epidemic for the entire production time‐course, however, was not affected by N fertilization. Plant N content was positively correlated with PMDS and AUDPC (area under the disease progress curve), although most correlations were generally low. The results suggest that N fertilization at 120 mg N/L could help limit powdery mildew incidence without compromising begonia growth and quality. The data also show that at the traditional rates used today, little if any disease control benefit would be realized from K fertilization.

Keywords:

• Begonia
• Powdery mildew
• N nutrition
• Disease

Acknowledgments

This research was conducted under Hatch Projects 65‐0333, 65‐0376, University of Illinois, College of Agricultural, Consumer, and Environmental Sciences, and was supported in part by the Southwest Region of the American Begonia Society.