Have these problems always been here, but been overlooked, or are they really new problems that we are now having to deal with?
We have generally considered a Foliar Anthracnose
in the UK and caused by the fungus Sclerotinia homoeocarpa, both of these facts are now considered incorrect. We have long known that the causal pathogen is not S. homoeocarpa but its identity remains somewhat uncertain (if indeed the disease is caused by one pathogen alone). Generally now accepted as a Rutstroemia sp. of fungus, it has apparently now been seen on Poa annua in the UK. However, a recent molecular analysis of two known isolates of the Dollar Spot fungus taken from fescue in the UK and several isolates of a fungus isolated from suggested Dollar Spot on Poa annua has confirmed that the fungi from the Poa annua is ‘…a totally different organism’, (personal communication). Is it a pathogen causing Dollar Spot-like symptoms or is it a secondary infection that is developing on weakened Poa plants? Further work is currently under way, but I’m certain that the ‘is it or is it not Dollar Spot’ debate will run and run. We need to find the answer but, as you read on, you will hopefully appreciate that the answer may not be that straightforward to find. Back to our pre-2000 disease list and
we have Take-all Patch which, according to all texts of the time, suggested that this was a disease that only affects bentgrasses. We have always known that the fungus can infect other grasses and we are now recording an increasing number of cases of Take-all Patch on pure Poa annua swards.
Many fungi that cause disease are capable of living as both pathogens (causing disease) and saprophytes (on dead and decaying material), but exceptions to this include the Rust fungi and the fungus that causes Yellow Tuft disease which need to live on living tissues. Of those fungi capable of both parasitic and saprophytic lifestyles, some spend more time as saprophytes and can invariably be found on the older leaf tissues at the base of the sward. Does that mean that disease is always present? That depends on your definition. I believe it means that the potential for disease development in these cases is always present and one thing that remains unchanged over time is that a weakened sward is more susceptible to infection by these fungi or to increased disease severity.
weakened sward to be the result of maintenance or environmental stress - unbalanced nutrition, reduced nutrient or water availability, compaction etc. and, clearly, these and other environmental factors will stress the turf and increase its propensity to disease. But, we are becoming increasingly aware that they are not the only factors that cause stress. Over the past two or three years I have
received an increasing number of calls relating to reoccurring disease problems, primarily those of Microdochium Patch, Take-all Patch and Anthracnose diseases, where cultural management options and the correct application of plant protection products have apparently failed to relieve the problems. In effect, what was developing over a period of several months was a continuous, niggling infection that didn’t develop fully and never really went away. In all of the samples received for analysis from these situations, root depth was minimal, turf strength was reduced and root development was to varying degrees, deformed. High populations of plant parasitic nematodes were recorded in all of these situations and, with the mounting volume of data to support their possible involvement, it is becoming increasingly difficult to say that plant parasitic nematodes have no adverse effect on cool-season turfgrass development. In fact, in addition to being recognised as causing ‘extensive losses in turfgrasses in warm temperate and subtropical regions’, plant parasitic nematodes are now generally considered to cause a ‘chronic debilitation of grasses’ in cooler regions too.
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