Horticulture Document Library

This is a powerful, but focused document repository designed to connect our research-based scientific literature, trade and association magazines/websites with a comprehensive internet search.




Illinois State Florists' Association


THE GROWER of pot plants should have less trouble with plant diseases than any other crop production spe cialist in the greenhouse industry. By using a reasonable amount of care and paying attention to certain details, he should be able to keep diseases almost completely under control. However, certain diseases still cause considerable difficulty at times. Only a few of the most troublesome ones that plague pot plant growers are discussed here. THE POINSETTIA ROOT ROT COMPLEX The root rot complex is the most serious problem fac ing the poinsettia grower today. In recent years growers in all sections of the United States have lost entire crops, with the result that some have given up poinsettia pro duction. The disease is called a complex because three differ ent fungi are involved, either separately or in combina tion. These fungi are Pythium ultimum, Rhizoctonia solani, and Thielaviopsis basicola. They differ greatly in structure, growth habits, methods of reproduction, and response to environmental conditions. There are two periods in poinsettia culture when rots are most prevalent—soon after cuttings are potted, and just before the plants mature for Christmas sale. Occasionally the rots occur on cuttings in the propagat ing benches also. The first phase of root rot appears just before or soon after the cuttings are rooted, and is caused chiefly by Rhizoctonia and Pythium. The second phase appears as a late-season rot, just before the plants mature. In older plants Thielaviopsis is the primary pathogen, but if Rhi zoctonia and Pythium also are present the root injury is more extensive. Pythium ultimum This organism commonly initiates infection near the root tips, particularly in small roots. Once infection has occurred and conditions are favorable, the fungus gradual ly progresses up the root system. In cases where disease is mild, infection may be limited to the few roots ori ginally infected, but these are usually completely destroy ed. This is especially true at high soil temperatures. Under conditions of low soil temperature and high soil moisture, most of the roots become infected, and the entire root system is destroyed in time. Pythium root rot is charac terized by a light-brown color and a definite water-soaked appearance. A stem rot may also result from Pythium in fection but it is not common. Plants attacked by Pythium alone are dwarfed but leaf drop is usually not conspicuous

Source: • Illinois State Florists' Association Bulletin # 258

Keywords: Pythium High soil temperatures Dwarfed Root system Rhizoctonia solani Thielaviopsis basicola

Libraries: Floriculture

Download All Documents