Tech Notes Issue 11
Although not the Same as Chilling on Warm Season Turfgrasses, Cool Temperatures Can Cause Purpling
With cool wintertime weather creeping bentgrass and wintergrass putting greens can turn a purplish color. The purplish color may appear uniformly across the green, but is more likely to appear as patches on older creeping bentgrass and wintergrass greens. The purpling is most pronounced on 'Penncross' greens but can occur on all bentgrass cultivars. There can be a difference in purpling intensity among biotypes or clones that develop in these wintergrass and/or creeping bentgrass greens.
In most cases the purpling is a physiological response to warm sunny days followed by a rapid drop in temperature at sundown. Daytime temperatures in the 16's to lower 20's followed by nighttime temperatures in the single digits are optimum condition for purpling. Under these conditions the turfgrass plant is actively photosynthesizing and creating sugars during the day. At night the sugars are translocated down into the storage areas of the plant. However, if temperatures drop rapidly at sundown the sugars are trapped in the leaf and fail to translocate.
The sugar molecules left in the leaf attach to a plant pigment called anthrocyanin (purple or blue pigment). The buildup in anthrocyanin results in the expression of the purplish color. Once warmer temperatures arrive, the purpling will diminish. If symptoms do not disappear with the arrival of warmer temperatures, check your soil test reports for phosphorus deficiency. Symptoms of a phosphorus deficiency are purple leaf blades.