Disease
How often has it been said that effective turfgrass disease management depends on early and accurate identification of the problem. Today, this is arguably more important than ever
DR. KATE ENTWISTLE is one of the leading Turfgrass pathologists in the UK. Based at the Turf Disease Centre in Hampshire, she explains the process of identification required to accurately determine what you’ve got
diagnosis is a process that involves not only identifying the presence of potential pathogens but also understanding how those pathogens can damage the turf and recognising the progression of symptoms on affected plants. It is possible for any symptom of damage, for example chlorosis of the leaf, to have more than one cause and therefore, to recognise one symptom in isolation and to assume the cause of the damage based on that one symptom, could lead to serious errors in diagnosis. If the problem is misdiagnosed, any implemented disease management options could well provide no effective control and may even allow the damage to progress unchecked. At best, both time and money will have been wasted. At worst, the result
D
iagnosing disease is not the same as identifying a pathogen. Disease
might be lasting damage to the sward.
SO what questions do you need to ask yourself when trying to identify disease?
What symptoms are present on the sward? With regard to disease, it doesn't matter if the cause is in the root, crown or leaf tissue, you will ultimately see symptoms on the leaf. Are the symptoms generally affecting the whole sward (as with leaf spots) or are there discrete patches developing (as with take-all patch). In addition to the spatial distribution of the symptoms, what other characteristics are there? Are the affected plants yellowing or becoming reddened in colour, are all leaves equally affected or is it the older or younger leaves that are discoloured. Are there noticeable spots or lesions on the leaf or is the whole leaf blade equally affected. Is there any evidence of fungal mycelium or so-called watersoaked leaf tissue where the leaf loses structure and
appears wet and slimy to the touch.
What grasses are affected? In a mixed sward, knowing which grasses are affected can be a great help in identifying the disease. Although fungi are capable of causing infection on different grasses, most fungi will preferentially infect one grass type over another in a mixed sward and the grass preference will vary depending on the specific fungus. Also, the symptoms caused by one fungus may vary considerably on different grass types.
When did the symptoms first appear? This is important to know because some fungal diseases can progress very quickly and so knowing when they appeared and what they looked like when they were initially noticed, can help to identify the type of fungus that may be causing the damage.
How have the symptoms changed since they were first noticed? This is also very important because it will
tell you how quickly the problem is developing or spreading and how the symptoms change with 'maturity' of the disease.
What products have been applied to the turf in the past 7 to 10 days? Certain products can stimulate the development of some diseases by ‘weakening’ the plant or affecting the pH of the rootzone, for example. Plant protection products can affect the growth of fungi, either by reducing their presence in the sward or in some cases, stimulating them. Knowing whether or not they have been applied is critical if an accurate analysis is required.
It is not unknown for symptoms of damage that strongly resemble turfgrass disease to be caused by environmental/rootzone conditions or occur as a result of product applications. Localised areas of various grasses in a mixed sward can react differently to prevailing conditions and lead to
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Turfgrass
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