Dr Kate Entwistle sees red, but is it a disease or a natural physiological problem?
RED TURF - Whatever next? I
n 1999, Dr Peter Dernoeden wrote an article in Turfax that explained two of the common causes for why turfgrasses develop red/purple discolouration, and I will pick up on some of his comments here. His article is readily accessible and well worth a read, especially if you manage turf that routinely shows this patchy discolouration.
Although this discolouration of the turf often appears as distinct, disease- like patches across the sward, I believe that the most common cause for the symptom is a natural development within the plant. To explain what is happening, we need to look at the process of photosynthesis and what happens to the sugars that are produced by this process.
During the spring months, as day- time temperatures and light levels increase, turfgrass plants start to increase their rate of photosynthesis. The result of photosynthesis is the production of carbohydrates or sugars (photosynthates) within the leaf that will ultimately be used in other physiological processes throughout the plant. During the normal course of events, these sugars that are produced during the day-time will be translocated out of the leaf and into the crown or root tissues during the night, where they will be stored or used as necessary within the plant. However, as with all physiological
being fungal. However, in many cases, the reddening of the leaf is nothing to do with fungal activity but the cause is a
of these two problems and also to mention a third potential cause for this observed turf discolouration
of the year and the aim of this article is to identify the causes
cause a reddening to turfgrass plants during the same times
natural phenomenon that will not result in any lasting damage to the turf. There certainly are fungi that can
red/purple discolouration can develop on close mown turf, and the cause is often automatically regarded as
During the late spring and autumn months, patches of
processes, the rate of this translocation is affected by temperature and, as temperatures fall, the rate of movement is reduced. If night-time temperatures are low, anything from about 7O
C and
below, the translocation of these photosynthates will be significantly reduced, and this will lead to their accumulation within the leaf. These photosynthates/sugars are often quite naturally bound to other molecules within the plant, producing what we refer to as ‘anthocyanins’. There are various anthocyanins within the cells of plants and their colour and quantity will vary depending on the plant and the ambient environmental conditions. These anthocyanins are quite naturally found in healthy plants but their presence is often masked by the overwhelming presence of chlorophyll which makes the grass appear green. As the photosynthates accumulate in the leaf under cool night-time temperatures the leaf colour will change from green, through purple to red.
However, if this foliar discolouration is a natural event (caused by the
Since this accumulation of the anthocyanins in the leaf is a normal process, the effect will be reduced as night-time temperatures start to increase. There is no need for any product application to manage the symptoms, nature will do that, and without any lasting detriment to the health of the plant.
One way of telling if this natural phenomenon is the cause of the patchy discolouration, is to look at how the red/purple colour is developing on the leaf. If the discolouration is affecting much of the exposed leaf blade and, more specifically, if it is only developing on the upper surface with the underside of the leaf remaining green, you can be sure that the problem is physiological. Bentgrasses are quite prone to this reddening and different bentgrass species and cultivars will develop the discolouration to varying degrees. Poa annua can also be affected and an example of the discolouration is shown in Figure 1. However, as I mentioned at the beginning of the article, there is also a potential fungal cause for the reddening of turfgrasses during the spring and autumn months and it is important to be able to distinguish between these problems.
The fungal disease that causes similar
accumulation of anthocyanins within the leaf that have been produced during day-time photosynthesis but not translocated out of the leaf due to cool evening temperatures), why would all plants in the sward not become equally affected and the entire turf turn red? The plant is a complicated set of physiological processes and different plant species will naturally react differently to any given set of environmental conditions. It is a fact that, for example, in a close-mown Agrostis - Poa annua sward, all grasses will experience an effect on photosynthesis during warm, bright day-time conditions and cool nights but that some grasses will be affected to a greater extent than others.
Certain cultivars of a given grass type will show a more extreme reaction, producing greater amounts of anthocyanins or being able to translocate less as temperatures fall. Established turf will naturally segregate in to areas dominated by different species or clones of a grass type and this segregation may not be apparent when the plants are not under physiological stress. However, their differing response to ambient conditions can show up as a patchy discoloured sward.
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