Circadian Clock Controls Sunflower Blooms, Optimizing for Pollinators

Jan 18, 2023

By Andy Fell

An internal circadian clock controls the distinctive concentric rings of flowering in sunflowers, maximizing visits from pollinators, shows a new study from plant biologists at the University of California, Davis. The work is published Jan. 13 in eLife.

A sunflower head is made up of hundreds of tiny florets. Because of the way sunflowers grow, the youngest florets are in the center of the flower face and the most mature at the edges, forming a distinctive spiral pattern from the center to the edge.

An individual floret blooms over a couple of days: On the first day, it opens the male part of the flower and presents pollen; on the second day, the female stigma unfold to receive pollen. Somehow, florets coordinate so that they open in concentric rings starting from the edge and moving inward on successive days, with a ring of female flowers always outside the earlier-stage, pollen-bearing male flowers.

Pollinating bees tend to land on the ray petals around a sunflower head and walk toward the center, said senior author Stacey Harmer, professor of plant biology, UC Davis College of Biological Sciences. That means that they will pick up pollen after they have walked over the female florets, then carry it to a different flower head.

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Video: Dicamba Returns for Georgia Farmers: What the New EPA Ruling Means for Cotton Growers

After being unavailable in 2024 due to registration issues, dicamba products are returning for Georgia farmers this growing season — but under strict new conditions.

In this report from Tifton, Extension Weed Specialist Stanley Culpepper explains the updated EPA ruling, including new application limits, mandatory training requirements, and the need for a restricted use pesticide license. Among the key changes: a cap of two ½-pound applications per year and the required use of an approved volatility reduction agent with every application.

For Georgia cotton producers, the ruling is significant. According to Taylor Sills with the Georgia Cotton Commission, the vast majority of cotton planted in the state carries the dicamba-tolerant trait — meaning farmers had been paying for technology they couldn’t use.

While environmental groups have expressed concerns over spray drift, Georgia growers have reduced off-target pesticide movement by more than 91% over the past decade. Still, this two-year registration period will come with increased scrutiny, making stewardship and compliance more important than ever.