The purple coloration of turf plants at this time of year may raise some concerns for turf managers, and it may have some justification.
It is the time of year when the day length is increasing, which we all love, and the temperatures are warming, which we also agree is a good thing! In the central US, this is also the time of year that cold air mass from the arctic mix with warmer air mass from the Gulf of Mexico, which can result in some fairly extreme weather such as heavy rains, storms and tornadoes. That being the case, there may be situations where there is plenty of sunlight for photosynthetic activity, but the temperatures may play an adverse role on biological activity within the turfgrass plant. The result is that plants may run into an “overload” of sunlight, creating a problem called photoinhibition (1). Photoinhibition is when there is too much energy for the plant to handle and thus there may be damage to the photosynthetic apparatus. This will be noticed where leaf tissue, instead of greening, will start to show some brown or yellow tips prior to spring green-up, depending on the grass’s ability to adjust to this situation. Some turf may or may not also turn a color purple.
The color purple explained: Turfgrass plants and other plants have a system to avert complete disaster. Pigments other than chlorophyll can absorb light in the leaf and the color purple is associated with this. The purple / red color is created by flavonoid called anthocyanins (2). These pigments can exist in a range of colors and are associated with a variety of situations related to plant stress. In the case discussed above they operate in two ways. You will notice the color is predominantly on the top of the leaf surface – the area that faces the sun directly, and they are found in the outer cells of the plant leaf or epidermis. In this situation they act as a barrier to the actual light color we see due to its reflection. This can be deep red or purple but can also extend back into the blue light region depending on chemistry. These two portions of the light spectrum are most important as far as energy for excitation and photosynthetic activity. In a situation such as above where there is reduced capacity, the pigment is perceived to offer protection from the excess light levels. The pigments also absorb light in the 500-520 nanometer region of the light spectrum, further reducing the impact of green light on stressed photosynthetic apparatus.
In a recent turf sample pictured above, the redness also occurred. This turf was taken from a flooding situation – none the less a problem for photosynthetic activity and the response across the field was a red tint to the surface. The flooding effect was one portion of the damage, however looking at the turf leaves, the plants which had a purple color were green underneath while tissue which had turned brown was lost and so the pigments may have helped the wider spread of damage.
You may also see the purple color in times of low phosphorous and particularly during water stress and chilling stress. The problem is not necessarily the color, but may it be indicative of something that we have not much control on at the moment in relation to light, temperatures and photosynthetic activity. In a couple of weeks it should dissipate and the spring green-up will occur. If it persists, consider testing for phosphorous levels in the leaf tissue.
1. Ehleringer J. 2006. Photosynthesis: Physiological and ecological considerations. In, Plant Physiology (eds.) Taiz, L. and Zeiger L., Sinauer Associates, Inc, Sunderland, MA.
2. Seigler D.S., 2002. Plant secondary metabolism, pp 151-193. Kluwer Publishers, Norwell, MA.
Author: Ed Nangle, PhD candidate, Dept. Horticulture & Crop Science.