A New Threat to Cut Flower Production


A survey of U.S. zinnia growers found a range of production systems, zinnia cultivars, and growing conditions, almost all of which may be susceptible or conducive to zinnia melt-down disease. Concern amongst this broad cross section of the industry highlights the need for further research on this problematic disease, which will be conducted over the 2018 growing season.

ASCFG Zinnia Research Project Survey Result

In total, 29 responses were received, and the findings represent only the opinions expressed by cut flower growers in the survey. The responses were received from Connecticut (1), Georgia (3), Illinois (2), Iowa (1), Louisiana (1), Maine (1), Maryland (1), Massachusetts (1), Mississippi (2), New Jersey (4), New York (1), North Carolina (3), Ohio (2), Tennessee (2), Texas (1), Utah (1), and Virginia (1) in the United States, and Ontario (1) in Canada (Figure 1).

Most of the respondents grew their zinnias in open fields (in ground) (83.3%). Just over 13% produced zinnias in hoophouses, and approximately 3% used greenhouse systems. More than half of the respondents (58.6%) reported postharvest disease of zinnia (zinnia melt-down) somewhat reduced salable quantity or quality of their zinnia crop. Only 10% of the respondents reported that zinnia melt-down caused major reduction on their salable zinnia crops, and over 30% of the respondents had no problem with zinnia melt-down issue but mentioned their concerns about the disease.

According to survey responses, the postharvest disease of zinnia was observed in Connecticut between July-August in 2016; Georgia between June-July beginning in 2012 until 2017; Illinois in August starting from 2009 until 2016; Louisiana between June-November in 2016; Mississippi in August 2016; North Carolina in May from 2015 until 2017; Tennessee between July-Aug in 2015 and 2016; Virginia between July-September from 2014 until 2016; and Ontario, Canada in July 2016.

Cut flower growers surveyed indicated that the cultivars ‘Benary Giant’ (42.9%), ‘Queen Red Lime’ (14.3%), ‘Oklahoma’ (14.3%), ‘Queen Lime Blush’ (4.8%), ‘Cactus’ (4.8%), ‘Uproar Rose’ (4.8%), ‘Zowie’ (4.8%), ‘Whirlygig’ (2.4%), ‘Mazurkia’ (2.4%), ‘Peppermint Stick’ (2.4%) and ‘Persian Carpet’ (2.4%) faced problems with zinnia melt-down issue (Figure 2).

Most of the growers surveyed indicated that they purchased seeds from a commercial supplier (93.3%), with only 6.7% of the growers purchasing zinnia seedlings from a commercial supplier. Only 3.4% of the growers indicated that zinnia seeds or seedlings were tested for the presence of plant pathogens by the seed/seedling producers, and another 3.4% indicated that they sent them to a lab for testing. Just over 10% of growers indicated that zinnia seeds were treated for the plant pathogens by the seed company or themselves with either fungicide or Clorox treatments.

Wells (51.5%), city water (21.2%), ponds or lakes (9.1%), rainwater (9.1), rivers or streams (6.1%) and ditches (3.0%) were the sources of the growers’ irrigation water. The growers were not using treated irrigation water to eliminate microorganisms except those who used city water. The majority (75%) of the growers used drip irrigation system in their production.

According to survey responses, only 7% of the growers indicated that no other crops were grown in the same area with zinnias; 34.9% indicated other cut flowers, 30.2% indicated herbs, and 27.9% indicated vegetables were grown in the same area with zinnias.

Of the 29 respondents, 31% used sanitizers (bleach, soap or alcohol swabs) daily or weekly for their cutting tools; 41% used sanitizers (bleach or soap) daily or weekly for their buckets, harvest bins and storage containers; 17% used sanitizers (bleach or vinegar) weekly for hard surfaces; 31% used sanitizers (a drop of bleach, Chrysal gerb pill or chlorine tablets) as needed for water; 17% used sanitizers (bleach, hydrogen peroxide or hot water) as needed for trays/pots.

The cut flower growers surveyed indicated that they used rotation (33.8%); 23.1% used cover crop/green manure; 18.5% always had a complete cleanout after each crop; 10.8% had complete cleanout only if there had been a serious problem in the previous crop; 4.6% provide a crop-free period; 3.1% conduct solarization in planting consecutive plants.

More than half of the respondents (58.7%) indicated that the environmental conditions were high temperature and high humidity when they had zinnia melt-down issue. More than half of the respondents (53.3%) believed that growing in the field, hoophouse, and greenhouses were likely starting points of their zinnia melt-down issue; 26.7% believed that postharvest was likely to be the starting points, 13.3% believed it to be seedling production; and 6.7% believed that seed production to be likely starting points of zinnia melt-down issue.

Future Direction

Zinnia samples will be requested in 2018 from the ASCFG community (APHIS permit and sample shipment instruction will be provided by Dr. Baysal-Gurel) and Tennessee growers will be visited monthly starting in June through September 2018.

Diagnosis will be done on cut zinnia flowers using diagnostic tools including but not limited to culturing, microscopy, chemical and pathogenicity tests, serology (ELISA, immunostrip tests), conventional PCR, and sequencing. This objective will also result in the development of a comprehensive pathogen collection that will be used in future research. Based on diagnostic results, the possible sources (seed, transplants, irrigation water, bucket water, rainwater, and soil) will be screened and tested using the same diagnostic tools.

Please contact Dr. Fulya Baysal-Gurel via at [email protected] or (931) 815-5143 if you would like to participate on this project by sending zinnia samples.

Fulya Baysal-Gurel, PhD

Assistant Professor

Fulya Baysal-Gurel, PhD
Assistant Professor
Tennessee State University
Otis Floyd Nursery Research Center
472 Cadillac Lane, McMinnville, TN 37110
Office phone: 931-815-5143; Fax: 931-668-3134
e-mail: [email protected]