Plant growth regulators developed for use on amenity turf have been extensively checked for turf safety and efficacy and should have no detrimental effect on the appearance of the sward
discolouration (usually tan or straw- colour) along much of the leaf. These fungi take nutrient from the leaf and therefore they need to continually move to adjacent plants to maintain their feeding from the sward. Because of this, areas of foliar fungal disease often appear as patches that enlarge in size over time with the active infections developing in the most recently affected leaf tissue and decay setting in where the damage had initially started. With root and crown fungal infections, symptoms tend to show up as the plants are put under increasing stress through the summer or, in some cases, when the plants are starting to put on growth following winter dormancy. In both situations, an area of affected plants is seen and the area tends not to increase much in size over time, but the severity of the symptoms generally intensifies as the root and crown damage progresses. In this case it is the effect of the plants reaction to limited water and nutrient availability that shows on the sward. Invertebrate pests also tend to damage
plant roots or stem tissues and will therefore effectively sever the sward from its roots as they feed. The turf symptoms again appear as if nutrient or water stressed but, in addition, the plants can be easily removed from the sward due to reduced root presence. We are now aware that certain plant parasitic nematodes also have the ability to cause damage to areas of amenity turf and, because these microscopic roundworms can develop fairly localised populations in the rootzone, the symptoms that develop on the sward can resemble those of fungal patch diseases.
One thing to be aware of is that symptoms developing with straight edges tend not to be related to disease or invertebrate pests but are most often found to be related to product application or maintenance. Some fungi can be moved across the sward in water and can potentially cause swathes of disease that appear to follow the path of water movement. Although these symptoms will appear as ‘runs’ of damaged plants across a sward, they will not have straight edges to them.
2. What has been applied?
A knowledge of recent product applications, or maintenance procedures
completed on the damaged turf, can help in finding the cause of the symptoms. Eliminating the possibility of scorch is sometimes very useful where you see a definite discoloration to the leaf tissues but the crown and new leaf growth appears healthy. Damage caused by product application tends to develop as a general effect across the treated area (e.g. if the wrong product was applied or the rate has been calculated incorrectly) or as definite straight lines following the direction of application (e.g. product overlap). Sometimes, products can affect the general physiology of the plant by adversely affecting the growing points (meristems) of the grass and this occurs through hormonal changes in the plant. Plant growth regulators developed for use on amenity turf have been extensively checked for turf safety and efficacy and should have no detrimental effect on the appearance of the sward if they are applied as specified on the label. However, other products may contain traces of hormones and, certain non- disease causing fungi that are naturally present in the rootzone, can produce hormones that may have an adverse effect on the normal growth of the plant if they are taken up by the turfgrass roots. Changes to the stem base/crown tissues can develop or plants may show rapid elongation of the leaf. In my opinion, both of these conditions can develop in turfgrasses through ‘accidental’ uptake of hormones but, although often short-lived, the adverse effects that they cause of the turf can be quite detrimental to the playing conditions of the sward.
3.Location of symptom development.
There are two aspects to this - firstly, what grasses are affected and secondly, what areas of turf are showing symptoms. Accidental or deliberate damage often shows equally on all grasses. Fungal disease tends to develop more rapidly on one grass type than another and cultivars can vary considerably in their susceptibility to infection. If symptoms are showing on areas of turf dominated by one grass type, this could give an indication as to cause. That said, the disease of Take-all patch which is generally considered to be a problem on bentgrasses, is increasingly seen on annual meadowgrass. Likewise, basal rot
anthracnose, which has generally been considered a problem of annual meadowgrass, has been seen in the UK on bentgrass turf. However, apart from identifying the specific grasses that are affected, it is important to identify where the problem is occurring.
Is it only on shaded turf, is it on the
more heavily trafficked areas or has it occurred equally across many areas at the same time? If the symptoms appear quite restricted, it is possible that the local conditions are encouraging a fungal disease or that accidental or deliberate damage has occurred. If the symptoms are extensive, it is possible that the problem is related to recent maintenance or to a pathogen that has responded rapidly to take advantage of a change in the environmental conditions.
Is it a pathogen or a pest?
So far, no one has formulated a foolproof plan to determine if adverse symptoms are developing as a result of fungal infection, invertebrate pest activity or damage. Similar symptoms appear to have been attributed to one or more likely causes and it is often the case that the cause of a problem cannot be identified from the symptoms alone. In identifying the cause of a problem, it is imperative to look for the presence of a biological cause (e.g. either fungus, nematode or other invertebrate pest) or, if there is none, to determine to possibility of a physical cause, a problem with the rootzone or damage. Invertebrate pests such as leatherjackets, chafers, Bibionid larvae, cutworms and frit fly larvae can be recognised in rootzone or plant samples, as long as you know what you are looking for and where to look. Finding the occasional one or two of these pests in turf that is showing damage or discoloration will probably mean that they are incidental to the cause. You tend to need populations to develop above damaging levels for symptoms to show on the turf.
The same is true for nematodes. Plant parasitic nematodes can be found in very low numbers (background population) in most rootzones or within roots but they will only have an adverse effect on the turf if their population develops above the known damage threshold. Populations tend to increase and fall
If the symptoms appear quite restricted, it is possible that the local conditions are encouraging a fungal disease or that accidental or deliberate damage has occurred
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