When diseases develop on turfgrasses, it is almost invariably fungi that are the cause of the problem. Under the right conditions, the symptoms of disease can develop and spread rapidly and in some cases, cause extensive and lasting damage. But when conditions are not conducive for disease development, what happens to the fungi? Dr Kate Entwistle, from the Turf Disease Centre investigates...
In the vast majority of cases, the fungi that are responsible for turfgrass diseases are permanently present on the sward or in the rootzone. The most obvious exception to this is in newly constructed areas where the microbial populations will naturally be very low. However, these areas will not remain free of microbial presence (or sterile) for very long and within a short period of time, both beneficial and pathogenic microbes will begin to colonise them. Once present, these microbial populations will fluctuate over time increasing and decreasing in response to the local conditions. But as far as the pathogens are concerned, once they have become established in an area, they are likely to remain. So why is disease not an everyday occurrence?
To answer this fully we need to take a closer look at the agents of disease; the fungi. The mere presence of a fungus that has the propensity to cause disease on turfgrasses, doesn't necessarily mean that disease will develop, nor indeed that it is the cause of any symptoms expressed! Although the fungi are an extremely diverse group of organisms, they share similar characteristics and life cycles. However, there will always be exceptions that may vary widely from the general model, but on the whole, the fungal life cycle can be described as shown in Figure 1. By appreciating and working through the fungal life cycle, we can understand why disease is not an everyday occurrence, even if the fungi that cause the disease are always present.