How heat stress affects bentgrass and poa annua

Every summer, we blame the sun when bentgrass wilts under 95-degree afternoons. The syringe hoses come out, fans hum and we fall back on the same explanation: It’s just too hot.

But research from the University of Georgia, Rutgers University, and collaborating turf programs suggests we have been looking at the wrong culprit. It is not just the heat; it is the plant’s physiology.

What heat does inside the plant

Recent work at the University of Georgia has focused on a mechanism of protein turnover under heat stress. Under sustained high temperatures, creeping bentgrass doesn’t simply slow down; it begins breaking itself down at the cellular level.

University of Georgia researchers evaluated five creeping bentgrass lines with varying levels of heat tolerance: the heat-tolerant lines S11-729-10 and BTC032, the heat-sensitive lines S11-675-02 and Crenshaw, and AU Victory, which showed intermediate tolerance.

Under heat stress, S11-729-10 and BTC032 performed better overall, maintaining stronger physiological function, including photosynthetic efficiency and cell membrane stability.

Protein degradation increased significantly under heat stress, indicating a structural failure within the plant. The researchers found that the more heat-tolerant line, S11-729-10, maintained protein content and improved heat tolerance.

Poa annua vs. bentgrass

Work at Rutgers University and other university programs finally puts data behind superintendents observing that Poa annua goes first under heat stress.

Under sustained heat, researchers documented that Poa annua showed faster loss of green color, reduced green cover, higher electrolyte leakage (a sign of cell damage) and less stable metabolic responses.

The takeaway is that Poa struggles because its system is less stable under heat stress. However, bentgrass doesn’t thrive in summer—it just holds together longer.

Why roots fail first

Pull a plug in July, and you will see shallow, declining roots. Past research at Rutgers helps explain why.

Researchers also showed that heat stress is, in many ways, a carbon economy problem. During periods of heat stress, cool-season grasses experience reduced photosynthesis, increased respiration and faster carbohydrate depletion.

Roots, as the most energy-dependent tissue, are the first to fail. That shift—from temperature alone to energy balance—helps explain why turf can decline even when irrigation is adequate.

Rethinking summer stress

The most important takeaway from this research is not a product or a single practice. It is a shift in perspective—from asking, “How hot is it?” to asking, “How is the plant functioning under heat?

Two putting greens at the same temperature can perform very differently depending on root health, carbohydrate reserves, metabolic stability and cultivar genetics. University programs continue to show that these internal factors matter more than the weather itself.

The research does not make summer easier, but it does make the challenge clearer. You cannot out-water heat stress or out-syringe poor rooting. Practical priorities include:

• Genetics matter more than ever.
• Protect roots at all costs.
• Manage carbohydrates, not just canopy.

What this means for turf managers

Research is shifting away from heat alone and toward how plants endure it. That shift is encouraging, because many of the factors that influence summer survival are manageable. Turf performance during heat stress is often determined well before the hottest day of the year, through decisions about cultivation, fertility, irrigation, traffic management and cultivar selection.