Tech Notes Issue 9

A Camouflage Turf Appearance is Due Most Likely to Cool Temperatures

Chilling injury is defined as low temperature stress in the absence of freezing (Levitt, 1980). It  readily occurs on warm season grasses growing in the subtropical to tropical regions when temperatures drop below 12 C in late autumn or early winter. In addition to temperature, high light intensity can enhance the chilling effect. Although chilling is most often associated with couchgrass, it occurs on other warm season turfgrasses.

Chilling injury causes several metabolic of physiological dysfunctions to the plant including 1) disruption of the conversion of starch to sugars (amylotytic activity), 2) decreased carbon dioxide exchange, 3) reduction in net photosynthesis, and 4) the destruction/degradation of
chlorophyll.

Given the range of temperature from freezing (0 C) to 12 C that chilling can occur symptom expression can vary. The most striking symptoms occur, again under high light intensities with rapid temperature drop to - or close to - freezing. Under this scenario symptoms are expressed in 24 to 48 hours. Symptoms appear as bleached out turf often in a camouflage appearance.

The bleached out leaves is due to rapid pigment degradation. Although we are not aware of any data or studies, the consensus opinion among researchers in this area is that the serpentine or camouflage pattern occurs because of differential settling of cold air. In other words cold air settles into the lower areas of the turf causing more injury, similar to what occurs in a valley or at the base of a mountain range.

At temperatures in the 8 to 12 C chilling injury occurs much slower and is not as drastic. Chilling symptoms appear more uniform and the turf color is a combination of purple, blue, and red shades due to the slow degradation of chlorophyll and the corresponding expression of other pigments and carotenoids.

Control

Preventing chilling injury is nearly impossible if temperatures get cold. If conditions can be predicted prior to occurring covering the turf may help reduce the severity. Most of the
practices mentioned work best if the chilling period is short in duration.  Covering the turf can reduce the effects of chilling but may not be practical for large areas.