Identifying the primary cause of turfgrass diseases has, arguably, become more difficult over recent years as we have become better able to identify differences between certain closely-related organisms and to recognise the potential of previously unconsidered pests.
Dr. Kate Entwistle asks ...
WHAT’S THE CAUSE OF YOUR DISEASE?
D
uring the past 5 years, research from the USA has confirmed the identification of new fungal turf
diseases, for example Dead Spot (Ophiosphaerella agrostis) and Waitea Patch (Waitea circinata var. circinata) and a disease caused by a fungal-like organism, namely Rapid Blight (Labyrinthula terrestris). Here in Europe, we have seen the diseases of Waitea Patch and Rapid Blight but, as far as I am aware, we have not yet had confirmed reports of Dead Spot disease. Is that because the pathogen is not present across Europe, the conditions favourable to disease development are not encountered here, or because we have not looked for it? It is not only fungi and fungal-like
organisms that are being reported as causing new problems on amenity turf. Other plant parasites are being recognised with increasing frequency and the time has come to ask the question - have these problems always been here, but been overlooked, or are they really new problems that we are now having to deal with?
If we consider the cool-season turfgrass diseases that were recognised prior to 2000, we could no doubt list several fungal problems including Fusarium Patch (now called Microdochium Patch), Red Thread, Anthracnose Basal Rot, Dollar Spot, Take-all Patch, Leaf Spots, Rust and Brown Patch (though never that much of a problem in the UK). By looking at each of these diseases in turn and considering how our understanding of the causal organisms has changed over recent years, you may be more than a little surprised with what you find. With regard to Fusarium Patch, its name
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change to Microdochium Patch reflects the fact that for some considerable time we have been aware that the causal fungus was not a Fusarium species. Microdochium Patch has historically been thought of as a winter disease and one that was controlled to a large degree by severe winters. It may, therefore, be a surprise to learn that frosts don’t kill the fungus, they merely slow its growth and some isolates of the fungus are still capable of growth at temperatures below freezing. Although it is true that the ideal conditions for the development of the disease are cool, wet weather and a weakened sward, Microdochium Patch can occur on any sward throughout the year as long as conditions are conducive. Different known strains of this fungus may account for differences in disease development and variation in the expression of symptoms between locations or under different local conditions. Red Thread disease was always
regarded as an indicator of low nutrition, but this disease is increasingly seen on areas receiving adequate amounts of balanced nutrition. During 2007, Red Thread was a common sight on amenity areas and its incidence was probably affected by the leaching effect of the heavy rainfall experienced in many areas of the UK.
Anthracnose diseases are true stress diseases and Anthracnose Basal Rot is a disease that frequently affects weakened Poa annua swards during cool, wet conditions. However, this disease is not restricted to Poa annua and has been seen in Agrostis sp. in the UK although, as far as I am aware, its relative incidence
is comparatively low. What is increasing, however, is the incidence of Anthracnose Foliar Blight, a disease that can develop on all turfgrasses and which is caused by the same pathogen. It may be worth mentioning here that Anthracnose diseases are no longer caused by the fungus Colletotrichum graminicola but the causal fungus has recently been re- named C. cereale. In the near future, the old name is likely to remain
commonplace in publications but as with Microdochium nivale and Microdochium Patch, the new name will become increasingly used and accepted. In addition to the name change,
research has shown that the fungus appears to be relatively host specific and, although it can infect grass types other than the one from which it has been isolated, it is less aggressive in the other grasses. Therefore, in a mixed Agrostis and Poa sward, an isolate from Poa will be able to infect the Agrostis but the severity of the infection will be lower than that seen in the Poa.
As for Dollar Spot - where do we start!? Previously known as a disease of fescues
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