Many greenhouse growers in the Northeast have had to deal with high humidity and cool temperatures this spring. These conditions can lead to increased populations of cyclamen mites, such as those observed at the University of Massachusetts Extension Plant Diagnostic Lab in May. The mite feeding damage also serves as a path for Botrytis, which can compound injury to the plants.
Cyclamen mite infestations may occur in spring, but are most common in the fall and winter. Cyclamen mites are spread by air currents, plant-to-plant contact, and workers. Chemical control is challenging because the mites prefer to feed in the buds, where they are at least partially protected from contact miticides. Miticide resistance develops rapidly and two or more applications may be necessary. When making multiple applications, be sure to alternate translaminar miticides with contacts.
Where feasible, immersion of infested plants into hot water for 30 minutes can give satisfactory control. Test each plant species first to see if it can tolerate hot water treatment. Predatory mites are available for biological control. It is best to have predators in place before the population of cyclamen mites reaches damaging levels.
Botrytis readily invades wounds and all plant tissue, especially senescent or injured plant parts. Like cyclamen mites, Botrytis requires high relative humidity and cool temperatures. The pathogen is ubiquitous in the environment.
Botrytis is best controlled by a combination of management of environmental conditions, sound cultural practices, and fungicide applications. Control weeds and remove plant debris from the greenhouse. Space plants to allow good air circulation, reduce humidity within the canopy, and minimize leaf wetness. Improve horizontal air flow with fans. Reduce humidity in the greenhouse by a combination of heating and venting in the evening, particularly when warm days are followed by cool nights. Water in the morning and avoid overhead watering if possible.
Check out this University of Massachusetts update for more information.