0 Influx of diseases

Influx of diseases

By Laurence Gale MSc

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Autumn is the prime time when we see a great influx of turf disease. This is due to a combination of factors all prevailing at the sameDisease-triangle.2jpg.jpg

Diagram shows: A disease is caused by ay the interactions of the pathogen, host, and environment.

Most biotic or infectious diseases of turfgrass are caused by some kind of a fungal pathogen. Some diseases are genus (species) specific, whereas others can attack many turfgrass species. There are very few important viral and bacterial diseases of turf.

Disease susceptibility can result from a stress imposed by non-living agents such as mechanical or chemical damage and adverse environmental conditions.

Diseases

Fungi

Bacteria

Viruses

All of the common fungi pathogens survive in soil and mainly feed on dead plant matter but can, if the ideal conditions prevail, attack turf grass species. However, not all fungi are harmful, some are very beneficial in the breaking down of organic matter, with some able to stimulate plant growth as found with some strains of mycorrhizal forming fungi. This is where bacteria in the fungi help to fix Nitrogen and make it readily available for the grass roots. Examples of fungal disease include fairy rings, leaf spot and anthracnose.

Bacteria, like fungi pathogens, are able to survive and remain in soils for years and can be beneficial and harmful to plants. This again being dependent on the right conditions prevailing.

Viruses are pathogens with an extremely narrow host range. Viral diseases of plants are relatively rare. Infection is scarcely strong enough to kill the plant. Plant viruses have no specific mechanism for entering the host cell. Cell wall and cuticle are difficult obstacles for them to cross. Plant viruses depend, therefore, on injuries or on transmission via invertebrates (insects, nematodes, etc.).

Disease outbreaks usually occur when there is a high moisture content present, particularly on and around living and dead leaf tissue. The presence and onset of morning dews are the primary cause of leaf wetness at this time of the year. However, in recent weeks we have also seen some heavy downpours of rain that have increased the water content around the grass plants. The increased water allows disease pathogens to travel more easily between plants, until a weakened potential host is found. Fungi spores landing on a dry leaf surface do not in most cases, germinate or penetrate the leaf.

This increased water content coupled with continued warm air temperatures (recently recorded up to 20°C) has certainly encouraged prime conditions for diseases to promote and establish themselves.

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There are outbreaks of Fusarium, red thread, rust, leaf spot and many forms of fairy rings appearing on many turf grass situations. On a recent trip to Yorkshire I saw several different types of fungi growing on the same cricket outfield.

Early recognition and identification of a problem is essential to the maintenance of fine turf. Early symptoms of a turf problem rarely attract the attention of a non-professional. A subtle change in colour or growth rate, wilting or foot printing earlier in the day than normal, cottony growth on the grass in the early morning, birds or other animals actively feeding in the turf or a combination of these symptoms may be an indicator to a series of problems ahead.

The Groundsman/Greenkeeper/Manager must make regular (daily) inspections of the turf to establish a reference by which abnormalities can be readily recognised. For example, difference in soil conditions may cause the grass in one area to wilt sooner than in another area. Also, changes in the colour or growth of a turf may indicate a nutrient deficiency and requires frequent observation to detect these problems in their infancy.

Maintaining a daily diary in enough detail to show what, when, why and how with respect to management practices performed is helpful. Fertilisation records can help explain changes in turf colour or growth rate. Include cultural practices such as mowing, watering, aeration, vertical mowing and topdressing in the daily records.

In addition to the records of daily operations, keep soil tests, water and plant analyses for several years for reference purposes. In critical situations these analyses could provide helpful information.

With the advent of digital cameras, the opportunity to photograph and acquire instant pictures of the disease is a valuable weapon which can be used to help identify the disease decide on the course of action and record at what stage the disease may be in its life cycle.

Understanding how disease pathogens behave is important, every disease responds differently and has different methods of reproduction. There are two main disease cycles that are responsible for spreading and promoting disease pathogens. The primary Disease Cycle (Monoocyclic Disease) and the Secondary Disease Cycle (Polycyclic Disease).

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Plant pathologists study these cycles to determine where cultural or other types of disease control tactics can be applied to interfere with the disease and thereby interrupt the process cycle. This in turn can reduce the incidence of disease or prevent the disease from spreading further. For example eliminating plant debris/thatch may reduce the ability of a pathogen to over winter.

Integrated Disease Management:

Keeping the sward healthy and reducing the conditions that favour diseases will be the first priority to keep turf disease free. The following actions should help you achieve this.

  • Carry out programmes of aeration to help keep the surface free draining.

  • Keep the sward mowed at a constant height.

  • Inspect and monitor existing surface water drainage systems, ensure that they are working.

  • Prevent moist conditions remaining on the surface by brushing / sweeping / switching the playing surface (remove dew) first thing in the morning.

  • Apply a balanced fertiliser low in Nitrogen (in winter) less than 3-4% to keep the sward healthy. (A soil analysis will identify other fertiliser requirements).

  • Control thatch layers as the organic material provides a good environment for the disease. (Reduction of thatch by hollow coring and scarification).

  • Stop or reduce the return of clippings to the sward. (An accumulation of dead matter will increase thatch).

  • Maintain Soil pH between 5.8-6.5 do not allow the soil to become alkaline.

  • Be vigilant and treat the disease early to prevent severe attacks. Treat with approved fungicides.

Fungicides

Fungicide formulations consist of an active ingredient (A.I.) and inert ingredients that may contain wetting agents, emulsifiers, or stickers that help to distribute the product over the crop and slow the weathering process down. Some fungicide products can have more than one A.I. to broaden the spectrum of the fungicidal activity. There are two distinct types of fungicides, contact and systemic, both are used to combat disease. Contact fungicides are most often applied as foliar sprays to protect above ground tissue from infection. This type of fungicide often requires repeat doses to treat diseases effectively.

Systemic fungicides operate in a different mode, the chemicals are taken into the plant via roots and the leaves, entering into the plants vascular system whereby it can attack the disease from within. Application of systemic fungicides is not weather affected, except when the plant isn't actively growing. Systemic fungicides will remain in the plant for longer periods-providing longer control.

There are a number of UK approved fungicides that can be used for treating diseases, all should be applied in accordance with manufacturers recommendations, product data sheets and COSHH regulations. (control of substances hazardous to health).

References:-Diagrams- Disease Cycles taken from Plant Pathology (Concepts and Laboratory Exercises) By Robert N Trigiano, Mark T Windham , Alan S Windham CRC Press 2004: ISBN-0-8493-1037-7.

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