ARS | Publication request: Response of azalea cuttings to leaf damage and leaf removal

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: March 29, 2012
Publication Date: April 13, 2012
Citation: Copes, W.E., Blythe, E. 2012. Response of azalea cuttings to leaf damage and leaf removal. Southern Nursery Association Research Conference. 57:287-290.

Interpretive Summary: Azalea web blight, caused by binucleate Rhizoctonia fungi, occurs yearly on some azalea cultivars during nursery production in the southern and eastern U.S. Azalea shoots collected for cutting propagation can harbor the pathogen, thus allowing the disease to be carried with the plant through the propagation process. A previous study demonstrated that submerging Rhizoctonia-infested stem pieces of 'Gumpo White' azalea in 122°F (50°C) water for 21 minutes could eliminate the pathogen without causing damage to leaf tissue. The present study determined that this hot water treatment can be used safely for cuttings of twelve commonly grown azalea cultivars without causing detrimental leaf damage or adversely affecting root development, despite the fact that hot water causes severer physiological stress on the cuttings than leaf removal. The information will be beneficial to university crop consultants, cooperative extension specialists, and commercial plant producers.

Technical Abstract: Binucleate Rhizoctonia species, the pathogens that cause azalea web blight, can be carried on stem cuttings, perpetuating the disease through subsequent crops. Previous studies have demonstrated that submerging Rhizoctonia-infested stem pieces of 'Gumpo White' azalea in 122°F (50°C) water for 20 minutes can eliminate the pathogen without causing damage to leaf tissue. Extending the treatment duration to 60 or 80 minutes demonstrated that some cultivars, but not all cultivars, could be injured with extended submersion in hot water. An important point was that a 20 minute plus margin of error exists where damage would be relatively minor if distracted workers accidentally left stem cuttings in 122°F water longer than intended. In the present study, an incremental increase in leaf damage from hotter water temperatures resulted in incremental reductions in final root development and final leaf count. Conversely, increasing percentage of physical leaf removal caused no reduction until at least 75% of the leaf area was removed. This demonstrates two important points: 1) water hotter than 122°F can severely impact the vigor and survival of stem cuttings, and 2) azalea stem cuttings generally can recover from partial leaf loss if given proper care.