control strategy has gained much publicity, particularly with the increasing concern in relation to possible environmental damage and human health risks stemming from synthetic herbicide use. Methods using natural weed antagonists to control weed growth have been used and these agents are commonly referred to as bioherbicides. Biological weed control consists of using natural pathogens to selectively injure target weeds. However, the pathogen must not injure desirable plants. A particular problem with the use of such control has been the ability of the antagonist to persist in the environment that they are introduced. Biological control is made up of two strategies:
• Classic control whereby an organism is selected that can establish and sustain in the particular environment.
• Inundative control which consists of repeat application of biological control agents.
These inundative biocontrol agents are applied at high concentrations for immediate effect. However, they do not sustain long-term weed damage and are often sensitive to environmental conditions. An example of inundation control using micro-organisms includes dandelion control using Phoma herbarum. Microbial inoculants containing selected blends of bacteria and fungi have gained much attention as possible tools to control both weeds and diseases in turfgrass. It has been shown that deleterious rhizobacteria can colonise the root surfaces of weeds and suppress growth while subsequently increasing growth of desirable plants. Xanthomonas campestris pv. Poa annua has been identified as an organism to control annual meadowgrass in turf sward's. The organism works by preventing water movement through the xylem of the grass, however it does not negatively impact upon most other desirable
grasses. Gange found that the addition of a fungal inoculant containing four species of arbuscular mycorrhiza, had a positive impact on Agrostis stolonifera total biomass and a negative impact on Poa annua total biomass. Research at University College Dublin by Butler and Hunter, found that application of a commercially available microbial inoculant containing both bacteria and fungi significantly reduced Poa annua germination in a bentgrass sward. In many instances Poa annua invades golf greens within a few years of construction and this research may be a useful strategy in controlling annual meadow grass established on golf greens. Pyricularia setariae has been found to be a biological control for green foxtail. Having said all this, I realise that many
readers will be thinking “where can I get these biological control agents?” Up to now, the majority of these agents
were commercially unavailable and this meant that talk about using them was useless. However, recently numerous microbial inoculants products have come onto the market. Many of these inoculants contain blends of micro- organisms, many of which are not specifically designed to control weeds. In my opinion, it is only a matter of time before mass production of specifically produced biological weed control agents are commonly available throughout the world. Many biological control agents are extremely new and their ability to control their host weed has not yet been determined. One problem that many in the industry have with microbial type products is the lack of consistency of the inoculant products. This was highlighted by Professor Alan Gange during a recent meeting when he noted that some of the micro-organisms contained within microbial inoculant products may not be alive when they are applied to a turfgrass sward and this needs to be addressed in
order to maximise the potential benefits of these products.
Another issue that may be a problem with microbial inoculants containing various species of mycorrhizal fungi is that some fungi contained within may be antagonistic to other fungi and reduce any benefit of applying the fungal product, suggesting that, in some cases, less fungal species within an inoculant may be more beneficial. In conclusion, I would like to state that it is essential that every effort is made to ensure that cultural practices are used to every advantage to control weed invasion. Research carried out at Michigan State University found that herbicide use, coupled with improved cultural practices are required to maintain maximum turfgrass cover long term. In my experience, biological control agents are a very useful method in helping to control weed mass in turfgrass. However, in modern turfgrass management, many people expect mass eradication of weeds using biological control methods and this is not possible. Biological control will not eradicate noxious weeds and residual levels of the weed populations must be expected. Instead, these agents help to reduce weed numbers to more acceptable levels. However, presently in many situations this is not acceptable to many people, although as herbicide regulations continue to become stricter we will have no choice but to seek the use of biological and cultural control methods in weed management.
About the author: Dr. Tim Butler is a Sportsturf Science Agronomist and Independent Expert on all aspects of Golf Course, Sports Pitch and Race Track construction, renovation, drainage, agronomy and environmental
management. Contact Tim at
timmbutler@hotmail.com
Contract spraying services for all sports facilities requirements
Fertiliser applications
Chafer Grub and Leather Jacket control
Supply and
Amenity Contract Services Ltd Catchdale Moss Farm, Eccleston, St Helens Merseyside WA10 5QG Tel: 01744 885098 Fax: 01744 886001
Email:
richard@amenitycontracting.co.uk
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