Technical
Creeping Thistles (Cirsium arvense)
Dandelion (Taraxacum officinalis)
Common Nettle (Urtica dioica)
well as encouraging users to think about cultural and biological alternatives, we can fulfill our obligation to maintain a healthy environment, now and in the long-term.
Either way you view it, it’s the law, and the implications on Active Ingredients such as Dicamba mean that selective herbicides that many managers rely on annually for effective weed control will be changing over the next year. Many of the herbicides that contain Dicamba are being phased out. The ability to purchase them will end on the 30th June 2015 and they will no longer be able to be applied after the 30th June 2016, the statutory use-up period.
What are the alternatives?
We can use the model of Integrated Pest Management (IPM), to review our strategy and create the solutions to the problems that we’re left with. Taking a broader perspective that may encompass a larger area can help us define how the problems occur, and help us define how we can control them. Understanding the physiological requirements of plants can help us reduce the circumstances that favour weeds and help us understand what environment our desired species requires.
It may even lead us to exploring other cultivars or species that can thrive.
Many of the weeds that we apply selective herbicides to weren’t a problem a hundred years ago. Prior to the Haber-Bosch process, nitrogen was only available to plants in limited amounts, although it makes up about 78% of our atmosphere. We’ve significantly changed the amount of nutrients that are available and cycling through our environment.
Sulfur is trapped in coal, but the industrial revolution released this sulfur, by burning it, into the air where it reacted with water and oxygen to form sulfuric acid. Sulfuric acid is a strong acid. It ionises completely to hydrogen ions. This created acid rain with a pH below 5.0 which went on to damage organisms such as crops, trees and mosses.
Prior to the industrial revolution, the trees were seen as clothed in mosses and lichens. This can still be seen in areas with good air quality in the UK, e.g. West Wales, Northern Scotland. However, over time, these mosses and lichens were killed off, particularly in cities where the air quality was poorest. The Clean Air Act changed this and we are now seeing a recolonisation into our cities of mosses and lichens. However, the species that are colonising are the ones which prefer nitrogen; an example of this is Leafy Xanthoria (Xanthoria parietina), indicating that the availability of nitrogen is having an effect on our environment.
The availability of nitrogen within a grass sward means that certain species which are able to capitalise on this abundance will proliferate, and they may not be the species that we want, e.g. Creeping Thistle, Broad-leaved Dock, Spear Thistle and Dandelions are all indicators of a high nutrient status. These can be effectively ‘starved out’ over time by ensuring that these areas aren’t fed and that the clippings are collected and removed to an area that can be enriched.
An example of this might be to think about where the arisings are placed after golf greens have been mown? If you are gradually enriching an adjacent area, you’re storing up
problems in the form of plants that may prove difficult to control in the future. Prevention is better than cure, therefore nutrient application and location are key to targeting a particularly competitive group of weeds. Likewise, ensuring that the seed that you are buying conforms to the highest standards will prevent you potentially bringing problem plants in. Reputable seedhouses routinely check that the percentage of weed seed is minimal. However, once weeds are established, we need to think about methods to control them.
Cultural control
Grass has evolved with a growing point that is below the height of herbivores. This enables the plant to be regularly mown whereas other species are apically dominant and intolerant of mowing. Species that are ephemeral and don’t have a root system that enables them to store nutrients can be easily eradicated by removing the top growth, e.g. Common Groundsel. Many of these species occur very quickly when the soil is disturbed, which is why it is important to gain control of these weed species before they become entrenched.
The amount of root material is an important indicator of how persistent particular plants can be, perennial species spend time becoming established before committing to a stage in their development which results in their multiplication. It is worth regularly surveying areas to identify what species are present and potentially might cause a problem in the future. It might not be necessary or desirous to eradicate every last individual, but defining what constitutes a population, which is a trigger point for action, should be defined as part of the monitoring process.
Himalayan Balsam (Impatiens glandulifera)
Yarrow (Achillea millifolium)
Japanese Knotweed (Falopia japonica) PC APRIL/MAY 2015 I 119
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