For those of you not under snow, you might be noticing purple patches on creeping bentgrass fairways and greens. The purplish or bluish-gray color may be uniform but more likely appears as patches on older creeping bentgrass greens. These patches represent segregated out clones of the creeping bentgrass. The purpling is especially evident on Penncross creeping bentgrass greens but likely will occur on all seeded bentgrass cultivars. The purplish color occurs when temperatures get cold in late fall and continue to persist through early spring.

During relatively warm sunny days (60 to 65 F) the plants are actively photosynthesizing creating photosynthates (sugars). At night the sugars are translocated down into the storage areas of the plant. However, if nighttime temperatures are cold, some of the sugars fail to translocate. The molecules left in the leaf attach to a pigment called anthrocyanin (purple or blue pigment). The buildup of anthrocyanin from this process results in the expression of the purplish color. The purplish color will persist through the winter and into early spring. Once temperatures rise and turf growth begins the purplish color will disappear.

The most common misdiagnosis that I have seen is that superintendents may think they have Drechslera melting-out.  In addition, phosphorus deficiency is often blamed.  Although not totally wrong, phosphorus is important in ATP and under the above scenario phosphorus can be slowly incorporated, the lack of soil phosphorus is unlikely.  However, if the symptoms persist check soil test levels of phosphorus to make sure a deficiency is not present.