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Turfgrass diseases
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Turfgrasses, like you and me, are living things, and like all living things, they have their sick days too. Of course, the grass wont be submitting an MC any time soon (let alone buy one), but there are days when we needed to treat them just like a doctor would treat a patient.  The trouble with this patient is, it won’t be able to tell you what it feels.

For diseases to occur, three things must be present in their most favourable state; 1. A host, in this instance; the turfgrass. 2. A causal agent (also known as a pathogen) and 3. An environment that is conducive for the disease.

For this article, we will limit ourselves to only discussing the “living” causes of disease.  There are other causes of injury or disease to turfgrasses that may be caused by non-living things such as, extreme temperatures, too much or too little water, not enough sunlight, oil spill, too low mowing cut, too much or too little fertilizer, unrepaired pitch marks or shoe marks, even if the said marks are made by a living golfer, the golfers playing behind him might be wishing him dead!

The main types of pathogen are fungi, bacteria, viruses and nematodes. We will ignore the debate whether a virus is considered a “living” thing or not.  Let’s not go there ok?  I need to submit this article tomorrow and I am way behind deadline as it is.

Fungi.

Most of our local turfgrass diseases come from this type of pathogen.  These organisms (usually microscopic, some can be as big as mushrooms!) do not have chlorophyll so cannot produce their own food by photosynthesis like normal plants. They get their food from either living plants (these are called parasitic fungi) or dead plants (when its called a saprophytic fungi).

 Saprophytic fungi are considered the “good guys” because they help in the decomposition of dead matter in the soil.  They turn these dead matter into nutrients available for turf.

Unfortunately, some of these saprophytes can turn into parasites (these are called facultative parasites) when the environment is right. Most turfgrass diseases come from these facultative parasites, sitting in the soil, feeding on thatch quietly, then when the turf is weak or there is so much humidity in the ground, it turns into a “bad guy” and becomes a parasite. 

Parasitic fungi can be transported by air currents, splashing or flowing water, insects, mites, other animals, mowers, machinery, shoes and grass parts.

Fungal diseases are controlled through the practice of good cultural practices like good irrigation and drainage (especially drainage), maintenance of proper pH levels in the soil, ensuring enough sunlight and air circulation on the turfgrass, correct mowing height and especially; growing resistant species and cultivars of turfgrasses for the area and climate.

Chemicals used to prevent or control diseases are called fungicides. There are two basic types of fungicides available.

Contact fungicides coat the leaves of the turfgrass plant with a chemical that kills a fungi when it comes in contact with the leaf. This type of fungicide may need to be reapplied about every week. It can be washed off by rain or be mown off. The other type of fungicide is a systemic, where the chemicals enter the plant and kill the fungus as it tries to infect the plant. These fungicides may be effective up to three or four weeks. 

Bacteria.

Only a few turfgrass diseases are caused by bacteria.  Bermuda stunting disease in South Florida is believed to be caused by the bacterium Clavibacter xylii subspecies cynodontis. Bacterial diseases are worse under such environmental stresses as low light intensity, high humidity, free surface water and cooler temperatures. 

Bacteria, like fungi, lack chlorophyll so cannot make their own food. But most bacteria feed on dead organic matter (saprophytes), but a few are pathogenic. Bacterias enter plant through small openings on the end of veins, stomata (tiny openings through which gas exchange occurs in leaves) or wounds.  Wounds are most commonly caused by mowing, vehicle an/or human traffic. 

Viruses

Very few turgrass diseases are caused by viruses.  In fact none is known in Malaysia.  The only widespread and serious disease is St. Augustinegrass decline or SAD.  Viruses are pathogens that can be seen only through an electron microscope.

Viruses produce disease by upsetting the normal growth processes of plant cells, causing the cells to produce abnormal and injurious substances, including more viruses!  The more obvious symptoms of virus infection are yellowing, stunting and loss of vigour due to destruction of chlorophyll.  Virus diseases are often confused with nutrient deficiencies or genetic abnormalities, pesticide, or fertilizer injury or other injuries. 

Nematodes

Nematodes are probably the most numerous multicellular animals on earth. They are usually microscopic, the largest being 3mm long. About 3 billion nematodes are estimated to live in an average acre of soil, most of them in the top 6 inches.  Even when parasitic nematodes are found associated with the roots of grass plants, fairly high populations of most species must be present for damage to occur.

Only a few of the 2,200 species of plant-parasitic nematodes feed on the roots of grass plants and cause disease. Nematodes seldom kill grass plants by themselves; however, they are capable of affecting plant health by reducing their root systems.  Nematodes feed by penetrating the root cells and eating the contents of the cells.  Fungi and bacteria commonly enter through these wounds.  Most nematode species are harmless, feeding on decaying organic material and other soil organisms. 

Nematodes are controlled by starting with disease-free planting material and following the best cultural practices to ensure steady vigorous turfgrass growth. If the results of a nematode analysis by a competent nematologist (yes there is such a person) show potentially serious population levels, a soil fumigant can be applied before planting or a nematicide can be applied to established turf. 

Integrated Pest Management

No serious article on pest and disease will be complete without touching on Integrated Pest Management or IPM.  IPM is a philosophy (and you thought we greenkeepers are just gardeners?) which uses a series of decision-making steps to manage rather than treat for turf grass pest or disease on a regular basis.  In IPM, alternate approaches besides chemicals are also considered and used.

Before the 1980s in America – unfortunately still going on in Malaysia – there was indiscriminate use of pesticide application to control pest in many types of crops or even livestock.  This includes the use of these so-called “preventive” application of pesticide or antibiotic even before the crop or livestock got infected. 

These created other problems like, secondary pest or diseases, pest or disease resistance, effects on non-target organisms (remember there are plenty of good bacteria and nematode around and even inside us), contamination of ground water or lakes or rivers and even the poisoning of users.

The golf course industry in US and in the world came under attack by environmentalists and thus IPM was born.  IPM deserves an essay of it’s own, which means I’ll have to stop here (Thank God, this is pretty boring, isn’t it?).  I’ll continue next issue with major pests of turfgrass and follow up with IPM and other environmental issues of golf courses after that.  

Reference:

Murdoch, Charles L. (1995) Regionalized Disease and Insect Identification and Control, GCSAA Educational Seminars. Singapore WTC.           

Ganapathi, Nathan Ph.D. (1994) Diseases of Turf and Integrated Management, Asean Plant Quarantine Centre and Training Institute.