Top Tips to Prevent and Treat Flower Fungal Infections

By Blake Jackson

This season has seen a flood of reports about fungal diseases across cut flower fields, nurseries, garden centers, and home landscapes. Prolonged periods of wet, humid weather have created the perfect environment for a range of fungal and fungal-like pathogens, including those that attack roots and crowns (like pythium, fusarium, and rhizoctonia), and others that target leaves and blooms (such as botrytis, powdery mildew, rust, and various leaf spots).

To effectively manage these diseases, it's important to recognize the common issues affecting your crops. Whether it’s powdery mildew on zinnias and phlox or botrytis wilting your dahlias before harvest, identifying the pathogen is critical.

Applying fungicides without a clear diagnosis may lead to ineffective results and unnecessary environmental impact. When in doubt, reach out to an Extension Educator or send samples to the Penn State Plant Disease Clinic for proper identification.

Cultural practices can help prevent or reduce fungal problems. Switching from overhead watering to drip irrigation keeps leaves dry and reduces disease pressure.

Improving soil drainage can prevent root rot issues. Sanitizing tools and equipment also minimizes disease spread. Choosing resistant plant varieties can further help protect your crops.

Some cultural methods, such as increased spacing for better airflow, may be impractical for commercial growers. And in particularly wet seasons, cultural controls may not be enough.

In such cases, fungicides can play a role but most are preventative, not curative. Early detection through regular plant scouting is key, especially on lower stems and leaf undersides.

When applying fungicides, rotate active ingredients by FRAC code to prevent resistance. Conventional options include etridiazole, mefenoxam, mancozeb, and chlorothalonil.

Organic and biological products, like those containing Trichoderma, Streptomyces, neem oil, copper hydroxide, or potassium bicarbonate, are effective and environmentally friendly alternatives.

Always follow label directions, including rates and intervals. Some products may require a surfactant for best performance. Lastly, flower growers should be cautious of pollinator exposure when using any chemical treatments.

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