Sunflowers may be iconic for their golden blooms, but for farmers and seed producers, these crops face a persistent and destructive threat: sunflower head rot. Now, thanks to a global collaboration among the world’s top sunflower disease experts, including The Iowa State University Seed Science Center’s (SSC) Dr. Charles Block, new light is being shed on these complex diseases and how to manage them.
Dr. Block, seed health testing coordinator at the ISU-SSC, is a co-author on a series of recently published diagnostic guides detailing the biology, epidemiology, and management of the major sunflower head rot diseases: Botrytis, Rhizopus, and bacterial head rot. These papers, titled “Sunflower Head Rot Diseases: Botrytis Head Rot and Bacterial Head Rot” and “Sunflower Head Rot Diseases: Rhizopus Head Rot,” provide comprehensive, up-to-date syntheses of decades of global research, offering valuable insights for plant pathologists, seed companies, and growers alike. Two additional entries in the four-part series are nearly complete. One focuses on Sclerotinia head rot and the fourth on Diaporthe and Phomopsis head rots.
“This is truly an international effort,” says Dr. Block. “There are a small number of sunflower pathology experts in the world, and bringing together that collective knowledge was critical to creating resources that are both thorough and practical.” The Sunflower Pathology Working Group (SPWG) started in 2013 with financial support from the North Central Integrated Pest Management (IPM) Center. The mission was to develop Extension materials such as disease diagnostic guides and other educational resources that would help growers and stakeholders identify diseases, pests, and nutritional disorders, and facilitate their ability to use IPM.
With nearly 40 years of experience in seed health, plant pathology, and the study of seed-borne and seed-transmitted diseases, Dr. Block brings depth to the team. At ISU-SSC, he leads seed health testing initiatives and also serves as co-director of the National Seed Health System (NSHS), a USDA-APHIS-authorized program that accredits public and private entities to conduct field inspections, laboratory testing, seed sampling, and visual examinations essential for issuing federal phytosanitary certificates for global seed movement.
“Understanding how head rot diseases operate at both the seed and field levels is key to managing their spread,” says Dr. Block. “In many cases, these pathogens are tied to specific weather patterns, crop residues, and even seed transmission. What we’re doing is connecting those dots across geographies and production systems.”
The publications detail how environmental factors, such as humidity, rainfall, and temperature, can trigger outbreaks, while also evaluating integrated management strategies including crop rotation, resistant hybrids, and targeted fungicide applications. “We were surprised at the level of interest the first two head rot papers generated from scientists around the world,” Dr. Block notes. “By sharing what we’ve learned, it will hopefully help others to better detect, manage, and prevent major losses.”
As sunflowers continue to grow in global significance, so too does the need for expert-led research and guidance. The SPWG collaboration reflects the rising global demand for more resilient sunflower production as the crop gains importance in food, oil, and bioenergy markets. As such, the research doesn’t just serve academic audiences; it’s a tool for regulators, producers, and industry stakeholders working to manage risk and improve yield.
Thanks to leaders like Dr. Charles Block, the seed industry has a trusted source of knowledge to turn to, rooted in decades of experience and a deep commitment to international collaboration and seed health.
The sunflower head rot review papers were co-authored by a distinguished team of international plant pathologists and researchers who are among the foremost experts in sunflower diseases. The group includes scientists from leading agricultural research institutions across North America and Australia, each bringing decades of field, laboratory, and extension experience. Their collective expertise spans fungal and bacterial plant pathology, disease epidemiology, integrated crop management, and seed health diagnostics. By combining regional insights and global perspectives, the team has produced authoritative resources designed to support growers, breeders, and regulatory agencies in addressing the evolving challenges posed by sunflower head rot.
Author names and affiliations are listed below:
Susan Thompson – University of Southern Queensland, Toowoomba, QLD, Australia
Malcolm Ryley – University of Southern Queensland, Toowoomba, QLD, Australia
Robert Harveson – Panhandle Research and Extension Center, University of Nebraska, Scottsbluff, NE, U.S.A.
Thomas Gulya – Sunflower and Plant Biology Research Unit, USDA-ARS Northern Crop Science Laboratory, Fargo, ND, U.S.A.
Charles Block – Iowa State University, Ames, IA, U.S.A.
Febina Mathew – North Dakota State University, Fargo, ND, U.S.A.
Samuel Markell – North Dakota State University, Fargo, ND, U.S.A.