Causal Pathogen

Anthracnose is caused by the fungus Colletotrichium graminicola. Although Anthracnose can affect other grasses, it is particulary damaging to closely mown Wintergrass (Poa annua). Colletotrichium graminicola is capable of surviving from season to season as a saprophyte in dead plant tissue in the thatch and on stems beneath the leaf sheath. It can also reside in the sheaths of grass plants. Once temperature and moisture reach favourable levels a new infection begins. Anthracnose is transported place to place via grass clippings.    

Anthracnose produces a characteristic fruting body called acervuli in warm weather. These black fuiting bodies, which possess black spines that protrude from them, can be observed with a hand lens or stereo microcope. Anthracnose can be found in the roots, stolons and leaves, but it is most commonly found on the foliage of the grass plant. 

 

Symptoms

Anthracnose is usually seen between mid to late summer to late Autumn. Anthracnose is characterised by irregularly shaped pacthes of yellow-orange turf, ranging in size from a few centimetres to a metre. Leaf lesions usually appear as elongated reddish brown spots on the leaves. These spots will enlarge, eventually encompassing the entire leaf blade. Acervuli can be seen on the foliage as the disease progresses, growing outward throgh the surface of the blade. Acervuli are particularly apparent on dead leaf tissue destroyed by the disease. In cooler, wet conditions, Anthracnose may cause a distinct rotting at the base of the plant.

 

Occurrence

Anthracnose is considered to be a 'biological indicator'. If the disease is present, turf growing conditions are likely to be poor. The disease is favoured by compaction. Low fertility and prolonged soil wetness also favour disease development. Results of laboratory studies show that the optimum temperature range for growth of the fungus is 22-31 degrees celcius. Inoculation studies show that Colletotrichium graminicola can cause disease on Wintergrass between 27 - 33 degrees celcius. Prolonged leaf wetness has also been proven to be important in the development of the disease.

 

Cultural Control Practices

Anthracnose can be managed with light nitrogen applications (0.25kg elemental N per 100Sq.m every 3 weeks - Vargas, 1994) when it occurs during cool weather.

Compaction should be avoided. This can be undertaken by moving the pin position regularly. Regular aeration or vertidraining is also beneficial. 

 

Chemical Control Options

Anthracnose can be managed with systemic fungicides applied every 2-3 weeks, or with contact fungicides applied every 7-10 days. Chemical control options are highlighted below;

 

Adama Fungicides

Evolution Fungicide

Compass Fungicide

 

Other Fungicides

Azoxystrobin – eg. Heritage Maxx.

Tebuconazole / Trifloxystrobin – eg. Dedicate.

Propiconazole – eg. Banner Maxx.

Azoxystrobin / Propiconazole – eg. Headway Maxx.

Chlorothalonil / Fludioxynil / Propiconazole – eg. Instrata.

The Causal Pathogen

The causal pothogen of Brown Patch is Rhizoctonia solani (Kuhn). Rhizoctonia solani is a soil borne fungus which can be found in the most soils and is known as a cause of disease in both established and seedling turfgrasses.

The disease does not produce spores, but instead spreads rapidly by mycelial contact. The disease is disseminated via movement of sclerotia which are produced and remain in thatch material.

Rhizoctonia solani has a characteristic mycelium over other patch diseases, whereby the mycelium branches at a 90 degree right angle, allowing for accurate diagnosis in the lab.

 

Symptoms

In Australia, Brown Patch is a disease primarily of the roots and crowns within the plant. The damage to turfgrass is in the form of a ring ranging from 5cm to 1-2m in diameter, with the grass in the centre of the ring usually remaining moderately healthy. The outer ring of grass turns brown and dies, usually from desiccation due to its damaged root system. When severe infection occurs, Rhizoctonia solani may infect leaf tissue also, making leaves appear water soaked, eventually drying and withering and turning brown. When humidity is high, a smoke ring, consisting of mycelial masses, may surround the perimeter of diseased patches in the morning. This occurrence dissapears as the turf dries out.

 

Occurrence

Rhizoctonia solani survives adverse periods as sclerotia / as mycelium on plant debris / or as a saprophyte in thatch. When soil temperatures rise to 15 - 20 Degrees Celcius, sclerotia germinate and the fungus begings to grow. Although growing at lower temperatures, Rhizoctonia solani does not infect plant tissue until air temperatures rise further and high humidity is experienced. Fidanza, Dernoedon & Grybauskus (1996) found that infection is likely to occur once minimum air temperatures rise above 16 degrees celcius and mean relative humidity increases above 75%.       

 

Cultural Control Practices

 

Nitrogen

High levels of nitrogen can increase the potential for Brown Patch infection. Hence, fertilisation with a high nitrogenous fertiliser prior to periods of high humidity should be avoided where possible.

 

Chemical Control Options

 

Chemical control options are highlighted below;

 

Adama Fungicides

Evolution Fungicide

Chief Aquaflo

Cavalry Weatherguard

Captan Fungicide

 

 

Other Fungicides

Azoxystrobin – eg. Heritage Maxx.

Tebuconazole / Trifloxystrobin – eg. Dedicate.

Propiconazole – eg. Banner Maxx.

Azoxystrobin / Propiconazole – eg. Headway Maxx.

Chlorothalonil / Fludioxynil / Propiconazole – eg. Instrata.

Mancozeb – eg. Penncozeb.

Trifloxystrobin / Iprodione – eg. Interface.

The Causal Pathogen

 

The causal pathogen of Dollar Spot is known as Sclerotinia homeocarpa. Microscopic diagnosis of Dollar spot is undertaken via its distinctive granulated hyphae which appears after a period of incubation. 

 

Symptoms

The disease is characterised by round, bleached out / straw coloured spots ranging in size from a few centimetres to several centimetres. The spots appear as sunken turf. Individual spots coalesce and destroy turf in large areas. Recovery from severe dollar spot can be extremely slow. With dew, greyish white, fluffy mycelium can be observed in the mornings.

When the diseased spots have progressed to bleached straw like stage, dollar spot lesions called 'stroma' can be found on leaves. These lesions are shaped like an hour glass

 

Occurrence

The Dollar spot fungus overwinters in the form of sclerotia and as dormant mycelium in plant crowns and roots of infected plants. The sclerotia appear as tiny, thin black flakes. Research conducted by Mills & Rothwell established that Dollar Spot Infection was high when maximum ambient temperatures are above 25 Degrees Celcius and Maximum relative humidity is greater than 90% during any 3 days in 7.

 

Cultural Control Methods

 

Low nitrogen levels intensify Dollar Spot damage. During periods of severe dollar spot infection, the nitrogen levels should be increased. Tank mixing Dollar Spot fingicides with a nitrogen source can be a useful strategy. Light and frequent Nitrogen applications is most efficient.

 

Removing dew or guttation water is a common practice on golf course greens which may assist in limiting dollar spot infection.

 

Chemical Control Options

 

Chemical control options are highlighted below;

 

Adama Fungicides

Evolution Fungicide

Compass Fungicide

Chief Aquaflo

Cavalry Weatherguard

Citadel Fungicide

Bumper 625

 

Other Fungicides

Tebuconazole / Trifloxystrobin – eg. Dedicate.

Propiconazole – eg. Banner Maxx.

Azoxystrobin / Propiconazole – eg. Headway Maxx.

Chlorothalonil / Fludioxynil / Propiconazole – eg. Instrata.

Trifloxystrobin / Iprodione – eg. Interface.

Thiram – eg. TMTD 600

Prochloraz – eg. Protak

Thiabendazole – eg. Vorlon

Causal Pathogen

Fungi from the Pythium genus are soil borne plant pathogens capable of causing different diseases on a range of turfgrasses. Pythium spp. can be a disease to both seedling and mature turfgrass swards. Pythium aphanidermatum and Pythium ultimum are the two most predominant turf infecting species.

 

Symptoms

The first symptoms of Pythium blight are circular reddish brown spots in turf, ranging in size from 2.5 - 15cm. In the morning dew, infected leaf blades appear water soaked and dark, may feel slimy and often mat together. As they dry, the leaf blades shrivel and turn reddish brown. On humid nights when dew form, you may see mycelium on the outer margins of the spots the next morning. The mycelium may remain active and visible far into the day, as long as there is plentiful moisture on the plant.

The infected grass plants collapses quickly. If temperature and relative humidity remain high, the spots may coalesce, and large areas of turf can be lost. 

 

Occurrence

Both species of Pythium survive as a saprophyte in the thatch, soil or both. When conditions are favourable, the disease invades roots as well as plant tissue and spreads from plant to plant via active mycelial growth. Pythium is a 'water mould' and survives well in waterlogged soils or on debris in ponds. Pythium can occur year round, however the disease is most severe when temperatures and relative humidity is high. Nutter et al found in 1983 that Pythium infection was likely to occur when  1) a maximum daily temperature was higher than 30 degrees Celcius, 2) followed by at least 14 hr of relative humidity greater than 90%, provided the minimum temperature was higher than 20 degrees celcius. More recent work undertaken by Shane in 1994 modified Nutter et al findings to the following infection requirements; 1) a maximum daily temperature was higher than 27.7 degrees Celcius, 2) followed by at least 9 hr of relative humidity greater than 90%, provided the minimum temperature was higher than 20 degrees celcius.

 

Cultural Control Practices

Good soil drainage will reduce Pythium activity. Hence, in areas where drainage is poor soil amendment maybe required. Thatch control and avoidance of over fertilisation are recommended for limiting the possibility for disease incidence. Good au circulation also helps minimise disease activity.

 

Chemical Control Options

 

Chemical control options are highlighted below;

 

Fungicides

Propamocarb – eg. Banol.

Fosetyl al – eg. Signature.

Thiram – eg. TMTD 600.

Azoxystrobin – eg. Heritage Maxx, Headway Maxx.

Metalaxyl M – eg. Subdue Maxx.