JOHN NEYL AN
Research
The organic herbicides trial was undertaken during 2021 to see whether they have a place within turf maintenance programs to eliminate Poa annua from couchgrass
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Agronomic expert John Neylan looks at a couple of research projects he has recently been involved with relating to the use of organic herbicides to control Poa annua in couchgrass and the use of recycled glass as an alternative rootzone medium.
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he control of herbicide tolerant/ resistant Poa annua in couchgrass fairways continues to be an ongoing challenge with no definitive solution. The use of glyphosate has become an accepted method of control where herbicides such as the sulfonylureas and propyzamide are failing. However, with the recent concerns about the use of glyphosate within the agriculture sector and the associated publicity, there has been an interest to see if there may be more acceptable alternatives. There are two organic weed killers that are based on plant extracts, available as nonselective total kill herbicides that are used in the production of organic certified crops. These weed killers have appeal because they are used in organic crops and potentially don’t necessarily have any of the negative impacts of more traditional herbicides.
Leaf tip burn from nonanoic herbicide at the 14L/ha rate
ORGANIC WEED KILLERS The primary source of organic herbicides is produced by plants (Webber et. al. 2012). Certain weeds and crops can release chemicals by exudation, leaching, volatilisation and from plant tissue decomposition (leaves, stems, roots, flowers) into the environment. 46
When these biochemicals (allelochemicals) come into contact with other plants they can influence (inhibit or stimulate) the growth of another species. The organic post-emergent herbicides are all non-selective, non-translocated, contact
AUSTRALIAN TURFGRASS MANAGEMENT 24.3
herbicides. In general, these contact herbicides control broadleaf weeds better than grasses, smaller weeds better than larger weeds and annual weeds better than perennial weeds. These herbicides destroy the plant’s waxy cuticle and cell walls causing desiccation and rapid wilting, which is further improved with the uniform application of the material. In trials undertaken by the Victorian Golf Course Superintendents Association (VGCSA) in 2021, two organic weed killers were selected. The organic herbicides selected are commercially available products used in the home garden and for organic certified crop production. They are both plant extracts and include a nonanoic acid (pelargonic acid) and a pine oil extract. Nonanoic acid can be found in pelargoniums in large quantities and is also produced in other plants when stressed. The trials undertaken during 2021 were based around the use of these products as an initial ‘look-see’ trial to see whether they have a place within turf maintenance programs.
METHODOLOGY The trial was conducted in the winter of 2021 using non-selective herbicides to provide ‘selective’ control of Poa annua