Cut Flower Updates: July 4, 2025

After a very wet May, where parts of the state received up to 6 inches more rain than normal, precipitation moderated in June across the state. Still, frequent rainstorms and hot, humid conditions have continued to present challenges for cut flower growers.

Growers are reporting continued fungal disease issues on flower crops. This week, we received reports of severe leaf and stem blotch on peony, a condition we usually don't encounter until later in the growing season. Warm, humid temperatures and frequent rainstorms, which can splash spores onto leaves, are likely to blame, particularly if there is a good deal of inoculum left over in the field from the previous season, a good reason to clean up your peony foliage this fall. 

The disease presents as shiny, reddish-purple to brown lesions on the leaves and red spots or streaks on the stems (sometimes called "peony measles"). Leaves where lesions are present may be curled or distorted. This condition is caused by the fungus Graphiopsis chlorocephala (formerly Cladosporium paeoniae), and can reduce plants' ability to photosynthesize at a crucial part of the season.

Scouting by Penn State Educator Kelly Piccioni in Eastern PA also revealed botrytis on dahlia and pythium on bells of Ireland, two diseases that have the potential to severely impact harvestability and lead to flower and stem dieback.

The fungus Botrytis cinerea commonly causes blight in dahlias, particularly when conditions are humid and cloudy, and where there is poor air circulation. On flowers, infection can cause browning and withering of petals, as shown above, progressing to fuzzy white or gray growth. The fungus can also impact tubers in storage.

Pythium is a fungus-like, soil-borne organism that causes root and crown rot, particularly in areas with poor drainage. Infected plants will look chlorotic and wilted, and roots will appear brown and soft with an outer layer that pulls off easily.

While there's nothing we can do about the frequent rainstorms and high humidity that characterize this part of the growing season, growers can try to reduce excessive soil moisture and wet foliage by addressing over-irrigation, particularly with overhead irrigation devices. Drip irrigation should be used where possible, and lines should be checked frequently for leaks. Scout often for early signs of fungal disease while conditions are humid and wet. Remove diseased material from the field as soon as possible to prevent the spread of spores. And remember to disinfect your snips between crops! 

Next week, we'll cover some fungicide options for conventional and organic growers as we keep an eye on other emerging issues in PA flower fields.

A reminder that if you haven't signed up for our email list, you can manage your Penn State Extension communication preferences and select "Commercial Cut Flower" as one of your preferred Areas of Interest.

Are you experiencing a pest, disease, or weed issue on your cut flower farm? Email Margaret Pickoff at mfp5667@psu.edu. We're always looking for new issues to explore in our weekly post.

Photos: Kelly Piccioni, Penn State Extension