The science of dew: Managing guttation to fight dollar spot

A golf course superintendent knows the visual relief of a heavy morning dew. It is nature’s quickest diagnostic tool: A crisp, uniform silver sheen across your fairways means your soil moisture is right where it needs to be. When the dew is absent, daytime irrigation tweaks are right around the corner.

While morning moisture signals healthy soil, it also acts as a primary catalyst for turf disease. Managing the “wetting period” — the total time the leaf blade stays wet — is a critical battle in the war against diseases, specifically foliar ones like dollar spot. How long that leaf remains wet directly influences the severity of disease outbreaks, making dew management a daily priority.

Insights into what makes up that morning dew might impact your mowing management decisions. 

Nightly dew is a complex cocktail of three distinct moisture sources: standard atmospheric condensation, distillation (moisture rising from the soil or nearby foliage) and guttation.

Guttation is where things get interesting for turf managers. This is the nutrient-rich plant sap exuded through specialized leaf pores called hydathodes or fresh mechanical cuts. Unlike pure atmospheric condensation, guttation water is heavily loaded with organic compounds, specifically sugars and amino acids. On a standard creeping bentgrass fairway, classic research shows that guttation accounts for roughly 33 percent of your natural nightly dew.

The real shift happens after your crews go out on the course. If you remove the dew early in the morning via mowing or poling, the moisture that re-accumulates isn’t just standard dew — it is overwhelmingly guttation fluid. In fact, data indicates that post-mow re-accumulation is anywhere from 46 to 77 percent sugar in the form of plant sap.

The “sticky ball” phenomenon 

You’ve likely seen the evidence of this high-sugar fluid yourself or heard about it from early-bird golfers. When a golf ball rolls across a putting green immediately after a morning cut, it picks up this sugary guttation fluid. Once it dries, the ball feels noticeably sticky.

Players can frequently complain about this stickiness, blaming it falsely on recent fertilizer or pesticide applications.

This high concentration of sugar is a potential problem for disease management. Fungal pathogens like dollar spot thrive on these carbohydrate-loaded droplets, using them as an easy energy source to supercharge infection.

Agronomic advice has focused on early morning mowing to knock down dew and disrupt the disease cycle. While opening fresh wounds on the plant via mowing does technically create entry points for infection, data proves that the benefits of shortening the dew period far outweigh the risks of wounding.  

Rethink morning routine

This is where your post-mow strategy becomes critical. Research by Michigan State University highlights a highly effective weapon against dollar spot: lightweight rolling immediately after an early morning mow.

Rolling isn’t just for boosting green speed. By rolling immediately after a cut, you mechanically knock down the newly re-accumulating, sugar-heavy guttation droplets. This breaks up the concentrated nutrient source before the fungus can feed on it and drastically accelerates canopy drying.

If rolling isn’t in your daily workflow, you have other highly effective options to mitigate this disease risk. Consider sending a crew member back out to pole the greens a second time to enhance drying, or program a quick, light irrigation cycle (“syringing”) immediately after mowing. A brief flash of water will dilute the concentrated sugars, keeping your greens cleaner, healthier and smoother for the rest of the day.