Watch for Botrytis and Other Disease as You Finish Poinsettias

Posted by Brian Sparks|November 13, 2023

This is the time of year to get your poinsettia crops past the finish line and out the door. In a recent e-GRO post, Jean Williams-Woodward of the University of Georgia notes that there has a myriad of disease issue on poinsettias this growing season including bacterial soft rot, Pythium and Phytophthora root rots, Rhizoctonia stem rot, Alternaria leaf spot, powdery mildew. and Botrytis. As bracts are coloring and temperatures are cooling, it is important to watch for anything that may damage the bracts. Calcium deficiency and Botrytis are two major issues that can cause bract burn and unmarketable plants.

“Botrytis blight can be explosive within greenhouses on damaged or senescing tissues where humidity levels are high (greater than 85%). The pathogen produces an abundant amount of spores on infected tissues that can be dispersed by water-splash and air movement to nearby leaves and adjacent plants. If you are not already using a fungicide to reduce Botrytis, you should consider it depending upon the stage of growth, sale date, and weather conditions in your area. Overcast, humid, and wet conditions will favor Botrytis infection,” the post says.

“Scouting for and managing Botrytis in greenhouse crops has been written about before in eGRO Alerts including “Scouting and Treatment of Gray Mold in Greenhouse Crops” and “Watch out for Botrytis”. The biggest concern about applying fungicides at this time of the poinsettia production cycle is concern for product residue and phytotoxicity on bracts in color. At this time, when the plants are about to head out of the greenhouse, Decree (fenhexamid) and Astun (isofetamid) are good choices. Other fungicides that are also good on reducing Botrytis are Affirm WDG (polyoxin D zinc salt), Broadform (fluopyram + trifloxystrobin), Medallion WDG or Spirato GHN (fludioxonil), and Palladium (cyprodinil + fludioxonil). Use of a surfactant can help reduce potential product residue problems. Always use products according to label rates and directions.

Learn more in the original e-GRO post here.