Thriving in cool, humid environments, Botrytis or gray mold can be particularly problematic in the fall. It can be most severe near the end of production
as the plants get larger and the relative humidity increases within the plant canopy. Gray mold is incited by the fungus, Botrytis cinerea, which
causes water-soaked spots on foliage and flowers. Once established, gray mold can infect stems and terminals causing wilting and collapse of the plant.
Under conditions of high relative humidity, the pathogen will produce masses of fuzzy, gray spores that can appear virtually overnight. Greenhouse
temperatures for poinsettia production are ideal for gray mold growth. White and pink, medium green-leaf varieties (e.g., Whitestar™ poinsettia,
Maren™ poinsettia, etc.) are generally the first to show signs of late-season Botrytis infections. As part of your scouting practice, regularly check
for "V"-shaped, tan-brown lesions that may develop along the margins of leaves and bracts and any tissue that has a brown/gray fuzzy appearance.
Conditions conducive for Botrytis infection are:
- Temperatures 62° - 75° F
- Relative Humidity >85%
- 4 hours of leaf wetness
Management practices that reduce relative humidity will help decrease disease pressure. Providing good plant spacing and horizontal air flow will help
improve ventilation and light access to the lower canopy, which can help in botrytis management. Periodically heating and venting the greenhouse to reduce
the relative humidity to 75% or less should also be considered. This is particularity important during cloudy, rainy conditions and prior to going into the
evening, when the relative humidity can increase. Avoid irrigating late in the day as this can also contribute to problems.
Botrytis is a high risk pathogen for developing fungicide resistance so it is important to utilize a product rotation with different modes of action. A
fungicide rotation includes Daconil® (prior to flower or bract formation), Heritage®
fungicides will provide protection
against Botrytis infections. Palladium contains two complementary modes of action with both contact and systemic activity on botrytis. Fungicide
applications should be made on a 14 day interval prior to disease development when environmental conditions are conducive to disease development. For
active infections, applications should be made on a 7 day interval. When making applications to bracts in color, the addition of Capsil® spray adjuvant
to Palladium or Heritage will help reduce residue.
Palladium 6oz + Capsil 4oz per 100 gal
Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties. Please check with
your state or local extension service to ensure registration status.
Some or all of the varieties listed herein may be protected under one or more of the following: Plant Variety Protection, United States Plant Patents,
Utility Patents, and/or Plant Breeders' Rights and may not be propagated or reproduced without authorization. Daconil®, Heritage®,
Palladium®, Maren™, Whitestar™ and the Syngenta logo are trademarks of a Syngenta Group Company. CapSil® is a registered trademark of