Identifying different lawn diseases
Proper treatment begins with the correct diagnosis.
To the untrained eye, lawn diseases like dollar spots, brown patches, and Pythium may look the same. Indeed, these and other diseases may share a few features which makes it doubly difficult to ascertain the specific disease which plagues your lawn.
The failure to correctly identify your lawn’s disease can aggravate the problem when you end up using the wrong treatment. So how do you distinguish one condition from the other?
Anthracnose
Anthracnose is caused by the pathogen known as Colletotrichum graminocola. A lawn that has been infected by this disease will have yellowish grass with red lesions. Upon close visual inspection, you may notice black fruiting bodies on the leaves.
Turf species like Festuca, Lollum, Poa and Cynodon sp. are particularly vulnerable to the disease.
The disease typically attacks lawns when the temperature goes beyond 25°C, usually between spring and autumn. The combination of high humidity and hot summer temperature in temperate climate zones as well as ample moisture can also lead to the disease.
Brown Patch
The combination of high temperature and high humidity, especially during late spring and summer, can lead to brown patches which typically affect bent grasses and fine fescues. However, warm season grasses can also be affected by this fungal disease.
If the lawn is mown closely, you may notice a greyish or purplish smoke ring around the perimeter of the affected areas on the lawn, especially in the morning when there are still dew drops. As the day advances, the colour of the smoke ring becomes tan.
If the lawn is mowed higher, it may appear thinner and in great need of moisture. In some cases, the centre of the ring may seem unaffected by the disease while the area encircling it may exhibit signs of damage and discolouration.
Dollar Spot
Dollar spot is another fungal disease that is characterised by the small spots, usually around 25 to 65mm in diameter, found close to one another. These spots appear to be sunken on the lawn and will have a brown colour.
Upon close inspection, these spots look paler and the infection usually covers the width of each leaf blade. In coarser turf species, the spots are diffused and affect just a part of the leaf blades. Affected leaf blades may also feel greasy or slimy to the touch.
The fungal disease, caused by Sclerotinia homeocarpa, can attack a diverse array of turf species. However, the most vulnerable species are the Zoysia, Cynodon, Kikuyu, and Agrostis.
The turf can become vulnerable to the disease when the soil’s pH level is less than seven, if there is poor drainage, humidity exceeds 90 percent for over nine hours, the daily minimum temperature is above the 17 to 20°C range, and the daily maximum temperature range is over 28°C.
Fusarium
Fusarium is a fungal disease that is caused by Microdochium nivale and typically attacks lawns when the temperature is around 16°C and when there is low humidity.
A lawn infected by the disease will have circular patches in areas that have been water-soaked. Each patch is usually no bigger than 5cm but can go as large as 20cm. Initially, the patches will have a brownish hue which will later become light grey.
Helmo
Helmo, also known as Helminthosporium, is a lawn disease that may be caused by different species of fungi, including Bipolaris, Curvulari, Dreschslera, and Exserohilum.
The disease requires a temperature range of 3°C and 30°C, high humidity, and ample moisture in order to thrive and survive.
Among the symptoms exhibited by the affected lawn include small dark patches, patches of dead grass about 10cm in diameter. Usually, the affected grass blades will turn yellow first before dying.
Pythium
This disease is caused by Sclerotinia homeocarpa and can affect both warm and cool grasses. However, Lolium and Agrostis are particularly vulnerable to the disease.
Pythium affects different parts of the grass. When the leaf blades are affected, the condition is called grease spot or cottony blight. On the other hand, if the affected parts of the plant are the root and crown, the disease is called Pythium crown or root rot.
The disease is characterised by small greasy spots on the affected parts. When these spots dry out, their colour will become yellowish to reddish.
Lawns can become vulnerable to the disease when the minimum daily temperature is above 17 to 20°C, the daily maximum temperature is above 28°C, and when the humidity is above 90 percent.
