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Trailed, rigidly fixed-tine spikers and slitters

Let us now consider pieces of equipment in which the tines are fitted rigidly to a drum, plate, or bar. As before, if a soil is well lubricated; minimal disruption will occur and the tine will merely create a slit in the soil, causing varying degrees of compaction and smearing. It is unlikely that soil aeration is enhanced. If a soil is in a drier state and friction is present; upheaval is likely but, again, there is a tendency for the soil to fissure along horizontal planes of weakness. It is for this reason that the turf tends to peel off at the depth of rooting. These implements may be effective in disrupting compacted layers or pans within the soil but are not very efficient at enhancing overall soil aeration.

Forking action: popularly referred to as verti-draining

We now turn to machines with a forking action, such as the Verti-drain, Soil Reliever, etc., that are designed to heave the ground. These can be effective if used when the soil moisture content is relatively low. Maximum heave and fissuring will occur in a dryish soil. The extent and direction of soil fissuring, and subsequent soil aeration, will be regulated by many factors; soil texture, structure, depth and expanse of rooting, and previous cultivation operations. However, a dry soil can cause unacceptable surface disruption and many turf managers choose, instead, to carry out the operation when the soil is in a moist to wet state. Under those circumstances, the effects

are very different. The heaving action now becomes a subsurface compaction action where soil particles are compressed together. A relatively large void may be formed but it is at the expense of surrounding soil macropores. If a soil is very wet, the implement will, at best, only produce surface drainage holes and soil aeration is minimal. In some

cases, it can

severely decrease the

potential for extensive soil

aeration. These

implements have proved very popular because of their potential to dramatically increase surface drainage rates. However, there is a major risk of achieving surface drainage at the expense of good internal aeration.

Air, water and amendment-injection implements

A number of machines are designed with very different principles in mind. Rather than relying on mechanical cultivation, they use either air- or water-injection to fashion a macropore system. The Sisis Aer-Aid System injects air; the Toro HydroJect blasts water; and a more recent introduction to the European market, the DryJect, uses water, followed by sand or another soil amendment, to modify the soil texture. Each of these machines is more effective in establishing a network of macropores and are, therefore, more deserving of the term ‘aeration’ equipment. The Aer-Aid has the potential to

increase a soil's macroporosity by preserving existing macropores and enlarging some mesopores. Theoretically, the mode of action pushes air through the existing pore system, thereby relieving compaction and encouraging an extensive and continuous network of macropores. The number and extent of macropores formed will depend on various soil characteristics. Nevertheless, such a machine is a dedicated aeration implement. The HydroJect, that injects fine bursts of water into the soil at the depth of penetration, will also create macropores and enhance soil aeration. It is generally more effective in coarse textured soils where few fine particles will migrate and clog pores. The machine can also be effective in the treatment of localised dry spots and general soil hydrophobicity. The DryJect combines the benefits of water-injection and soil modification. After establishing a hole and enlarging surrounding pore spaces by means of a powerful jet of water, the machine introduces dry sand or other amendments to stabilise the macropore system that has been created. Preservation of existing macropores and the creation of additional ones should be the aims of good soil aeration. The network of macropores must be extensive and continuous so that oxygen can readily diffuse to roots and soil microbes. As turf managers we must aid air movement uniformly throughout the rooting zone and not just limit it to sporadic vertical holes.

Above: Verti- Drain tines. Right: The

introduction to the European market.

DryJect is a recent

Each type of implement must be carefully considered and a knowledgeable selection can then be made to adequately correct the deficiency. Think hard about the problem and even harder about the remedy.

This disease is caused by the fungus Sclerophthora macrospora and unlike many of the fungi that caused disease in cool- season turfgrasses, this fungus is an obligate parasite. What this means is that the fungus must not kill the infected turfgrass plant because it needs to live on living plant tissue. In this respect, the fungus is similar to the rust fungi that can also cause turfgrass disease - but that is where the similarities end.

S. macrospora is capable of infecting and causing disease in most turfgrasses but it has become a relatively common problem on both bentgrasses and annual meadowgrass in close-mown swards. The mycelium of the fungus grows through the infected plants and will produce both resting spores within the infected tissues and, once the conditions are right, it releases motile spores which actively move in water films across the sward. Once present within the plant, the fungus can remain for many years, possibly the entire life of the plant, but symptoms of the infection will only become apparent under cool, wet conditions.

Initially, the infected sward will appear patchy as plants start to discolour and become pale and yellowed. Close analysis of infected leaves often shows a mild red colouration of the cells containing the resting spores but this is often only apparent under high magnification. As the disease progresses, individual plants are stimulated to produce excess tillers and this results in a tufted appearance to the sward. Close examination of the yellowing patches will also reveal a reduction in root development that will enable the tufted plants to be removed easily from the sward.

Since the causal fungus needs free water in order to complete its life cycle, the symptoms of this disease are often seen in low lying areas or in parts of the turf that are prone to holding water.

Infected plants can often be removed through verticutting or other grooming practices but management of the symptoms can be achieved through reducing the turf wetness and improving surface drainage. There is limited information regarding fungicide efficacy in managing this disease but general opinion would suggest that cultural management with regard to improving water movement away from the sward is the most effective means of reducing yellow tuft symptoms.

Dr Kate Entwistle MBPR, The Turf Disease Centre

Yellow Turf


disease OF THE MONTH

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