Okay, so Poinsettias don’t really get that many problems. But when issues arise, they can hit a crop fast and hard. Whitefly, Lewis mite, root rots, and nutritional issues can all quickly derail a quality crop.
OnFloriculture presents a month by month guide on what you should be looking for to prevent small problems from becoming big issues.
Erwinia and Rhizoctonia can look very similar infecting poinsettia cuttings.
Cutting Rots: The bacterial rot Erwinia (now renamed to Pectobacterium, just to confuse you) is one of the first diseases to appear in poinsettia, as is Rhizoctonia (a fungus). Check for soft and mushy cuttings, starting at the base of the stem and moving upwards. The cuttings will eventually collapse.
With Erwinia, cuttings will also smell funky, due to the bacteria. With Rhizoctonia, you may see white fungal strands near the crown.
Proper water management can help mediate both diseases; keep mist minimal overnight and turn mist off as soon as possible. Sanitation is also key to controlling their spread: make sure to immediately rogue out any propagation strips affected by Erwinia/Rhizoctonia, as all cuttings in the same strip are likely to be infected.
Root rots: July is also when you might start seeing the beginning of root rot issues in plug trays (especially Pythium, but also Rhizocontina, Phytophthora and even Fusarium). Although these won’t kill the rooted cutting outright, these diseases will proceed slowly and potentially cause large die-offs mid Fall. So make sure you’re regularly inspecting your cuttings to determine if you should treat now, to head off problems later.
Evidence of root rots include poor rooting, stunted growth, discoloured (black or brow) roots, loss of lower leaves and cankers on stems.
If you see these, then get the disease identified by the Guelph Lab Services so you can apply the appropriate chemical fungicide in propagation to help knock it back. Follow this with an application of an appropriate microbial fungicide like (like Actinovate, PreStop, Rootshield Plus, Taegro or Trianum; check the label) to boost root growth and continue to fight disease in susceptible cuttings.
Source: On Floriculture