Maintaining Plant Health Weeds Workbook Overview This workbook

Maintaining Plant Health Weeds Workbook Overview This workbook is designed to provide you with an overview of the principles behind the control of weeds. What am I going to learn about in this unit • What weeds are • The damage weeds do • The types of weeds and examples of each • The identification of common weeds • Methods of preventing the establishment of weeds • Methods of controlling weeds • Impacts on sustainability How will I be assessed in this unit By a series of questions linked to this workbook and the completion of a weed identification test

Weeds What are Weeds are plants that grow where they are not wanted! Why control weeds? Left uncontrolled weeds will Ø be unsightly Ø compete for water, Groundsel Senecio vulgaris Ø compete for space, Ø compete for light Øcompete for nutrients. ØThey can also harbour pests and diseases Weeds multiply very quickly either vegetatively by roots and shoots or through the production of seeds, often in large numbers. Weed types Annual weeds These complete their life cycle within a year. Some weeds such as Annual Meadow-Grass can produce more than one generation of per year and complete their life cycle in as little as six weeks. This type of plant is known as an ephemeral All parts of annual weeds die at the end of flowering and seed production, including the roots. These roots are usually relatively shallow and fibrous, making them easy to pull up. The large number of seeds that weeds can produce may result in problems in subsequent years. Even those seeds which do not germinate in the following year can remain alive in the soil for many years to come, and will germinate when cultivation exposes them to light and air. To avoid increasing the problem, annual weeds should be eradicated before they produce flowers and set seed. 2

Examples of ephemeral weeds include the Groundsel on the previous page and the following Chickweed Stellaria media Hairy Bitter Cress Cardamine hirsuta Annual Meadow Grass Poa annua Shepherds Purse Capsells bursa-pastoris Biennial weeds have a two year life cycle. Foliage growth often in a "rosette“ form takes place in the first season with flower and seed development occurring in the second year. Examples of biennial weeds: Spear Thistle, Cow Parsley, Wild Garlic, Ragwort Senecio jacobea Spear Thistle Circium vulgare 3

Perennial weeds can live for several years; at the end of the growing season the leaves dieback, but the roots and underground parts survive the winter and the foliage re-emerges the following spring. These weeds either have deep tap roots or extensive root systems and unless every part of the root system is removed or killed, the weeds will grow again. They can also regenerate from stem tissue and many set seed, as well. It is important to control these weeds before they become well established as they are more difficult to control once established. Dock Rumex obtusifolius Wood Sorrel Oxalis acetosella Creeping Buttercup Ranunculus repens Examples of perennial weeds: Dandelion, Daisy, Dock, Bindweed, Wood Sorrel, Horsetail and Creeping Buttercup. Dandelion Taraxacum officianale Daisy Bellis perennis Hedge Bindweed Calystegia sepium Field Horsetail Equisetum arvense 4

Weed Prevention & Control The prevention and control of weeds can be carried out in a number of different ways; the method selected is depending on the type of weed and its stage of maturity. Preventing the occurrence of weeds The best way of preventing weed problems from occurring is to prevent them establishing themselves in the first place. This is only possible if you start off with land that is clear of weed. Prevention methods include: Ø Mulching Ø Use of ground cover Ø stale seedbeds Ø sterile compost media and containers Mulching – This is the application of a layer of material over the soil surface to help to retain moisture and to suppress weed seed germination. NB Seeds will only germinate if they re in the top 1 cm or so. By placing about 25 – 40 mm of a weed free material over a previously weeded surface germination is prevented. Materials that are used for mulching These can be broken down to organic and inorganic materials: Organic Mulches – Bark chippings, Leafmould, garden compost, Coir fibre etc. In addition there are materials based upon corn starch that can be sprayed on the surface of hardy nursery stock potting media that act as pot mulch preventing weeds such as Hairy Bittercress from infesting the pots. Inorganic Materials – Materials such as clean gravel and pebbles make effective loose mulches. Woven polypropylene and other plastic fabrics can be used, these are often referred to as geotextiles. 5

Ground Cover This is a technique, where low growing and spreading plants are planted so that they entirely cover the surface of the soil, in order to shade out weeds and their seeds Both herbaceous and woody perennials are suitable, providing they have sufficient foliage density to do the job. Solomon; s Seal Polygonatum x hybridum Plantain Lily Hosta sp. Examples of Good Ground Cover Plants Include Hosta fortunei. , Houttuynia cordata, Lamium macculatum, Tiarella cordifolia, Epimedium rubrum, Erica carnea and Cotoneaster horizontalis, Pachysandra terminalis. Stale seedbeds Bishop’s Mitre Epimedium rubrum This is a technique where a seedbed is prepared well in advance of its intended use. Weed seeds germinate on this and are then hoed or sprayed off. This process may be repeated more than once. The object is to deplete the weed seed present in the upper surface of the soil before the intended crop is sown, thereby reducing any weed competition. Sterile Growing Media & Containers By using sterile growing media containing no viable seed and by ensuring that weed seeds are not introduced on contaminated containers and canes you can ensure that plants have a good competition free start. 6

Weed Control If and when weeds do become established, they need controlling and control measures fall into three categories: ØCultural ØChemical ØBiological Cultural Control Cultural control involves the physical removal or severing of weeds in such a way that they cannot re root or regenerate themselves or the use of heat to cause their tissues to collapse. The main cultural methods are Hand Pulling Hoeing Forking Out Heat Tools used for weeding Onion Hoe Dutch Hoe Draw Hoe Patio Knife Hand Fork Garden Fork Border Fork 7

Hand Pulling & Forking Out This is the removal of weed that his large enough to handle by physically pulling it out of the ground, including any roots. Annuals such as Groundsel (Senecio vulgaris) usually come away easily and these can be disposed of in the compost heap. For perennials however it is vitally important that all vestiges of roots are removed, otherwise they will quickly regenerate themselves. A hand, border or garden forks should be used to ease the entire root system out. The soil should then be shaken off the roots and the weeds removed and burned, to prevent them re establishing themselves in the compost heap. Hoeing There are essentially two types of hoe used in weeding, those that are used with a chopping action such as the draw hoe and onion hoe and those that are used with a cutting action such as the Dutch hoe and its variants. Whichever type of hoe is used they should only be used on annual / ephemeral weeds. Dutch Hoe – this is the preferred tool for weeding flower beds and borders because its action leaves the ground even and it disturbs the soil less than other types of hoe. Though it will tackle larger weeds it is best used on seedling weeds which once their roots have been severed by the hoe can be left to wither on the bed. Draw Hoe & Onion Hoe – These are ideal for vegetable or nursery bed weeding Their chopping action disturbs the soil more and they leave a less even finish; they can however, handle larger weeds than a Dutch hoe and are also used for drawing out seed drills and thinning out seedlings. 8

Use of Patio Knife – This is a useful tool for raking out weed from the joints between paving and other restricted places Use of Heat An alternative method of weed control that can be used on bare ground or paved areas is the use of heat. The normal method of applying heat is some form of flame gun. The gun is directed to the base of the weed, rapidly raising the temperature to 1000°C causing top growth to collapse and die. N. B. because of the insulating effect of the soil, deep rooted weeds will recover from adventitious buds forming on undamaged tissue. This sort of treatment will also kill weed seeds and spores on the soil surface. Chemical Methods of Control As an alternative to cultural control, chemicals can be used to prevent weed infestation or to kill any that might have established themselves. The chemical we use are known as weed killers or more often herbicides. Herbicides have different properties which affect how they work, how long they last and the types of weeds they control. The main modes of action are Contact Translocated (systemic) Selective Non Residual 9

Contact Herbicides: A contact herbicide will kill green parts of the weeds or plants to which it is directly applied. It will not be transported to other parts of the plant. It is thus suited to the control of annual weeds, but less so to the control of perennial weeds, as the roots are not killed. Regular use on perennial weeds will, however, weaken their growth over a period of time. Contact herbicides affect the surface parts of the plant Contact herbicides only control leaves and shallow roots; get re growth from deep rooted weeds. Translocated Herbicides: Translocated or systemic weedkillers are absorbed by plants and carried around the whole plant, including the roots. They are suitable for the control of both annual and perennial weeds but they do rely upon weeds being in active growth and are slower and less effective in periods of slow growth such as cold or drought. To get the best weed control from a systemic weed killer in dry weather it is advisable to water the weeds to get them into more active growth before treating them The most common translocated herbicides used in horticulture are based on Glyphosate which needs between 4 -6 hours without rainfall in order to be absorbed properly by weeds. If it rains in the interim, it may be necessary to give a further application. It is also a good idea to know what to expect in terms of weed control – Translocated herbicides take longer to show the effects of control than contact ones. 10

Translocated herbicides are absorbed by the plant and the poison is then moved systemically throughout the plant All parts of the plant including the roots are affected, so translocated herbicides are useful against biennial and perennial weeds as well as annual. Selective Herbicides: Some weedkillers contain active ingredients which will selectively control weeds with a certain type of growth habit without harming plants with a different growth habit. Lawn weedkillers are translocated herbicides that will selectively control broad leaved weeds without damaging the grass. Selective weedkillers may be either contact or systemic in their mode of action. Most weed killers currently available are non-selective i. e. they will cause damage to cultivated plants, as well as weeds, so care must be taken when the weedkillers are being applied. Non-residual: Non-residual weedkillers have little or no persistence in the soil and are therefore suitable for use where land is required for planting soon after application. Residual: A residual weed killer remains active in the soil for several months or longer, depending on the product and climatic factors. While it continues to be active weed growth is prevented. Most residual weedkillers are used primarily for long term total weed control. These products should not be used near established plants There are residual weedkillers which can be used prior to planting and/or around growing plants. They are generally suitable for use around shrubs and woody plants and can be very useful for use in the low maintenance garden or area, provided only woody plants such as shrubs or roses are grown. 11

Sustainability Notes on Weeding Reduction in Biodiversity – The very act of removing weeds involves the selection of some species (the cultivated plants) for survival and the destruction of others (the weeds) which obviously reduces biodiversity. This is inevitable and is mitigated to some extent if weeds are removed and either let lie to rot in situ or composted. In either case the materials that made up the weed are recycled to the soil and fertility is maintained. The process of decomposition and humification itself supporting many soil organisms. . However, we do tend to be too tidy in our gardens and if an out of the way area can be left to grow weeds such as nettles, they will provide a nectar and fodder resource for insects such as butterflies. Pollution -The use of heat as a method of weed control is very fuel inefficient, especially the use of steam, producing large quantities of the greenhouse gas carbon dioxide. The chemicals that made up the body of the weed are lost as gasses if the plant is completely incinerated resulting in a reduction in soil fertility. The use of herbicides as a means of controlling weeds brings with it the risk of chemical pollution of the soil and or watercourses and the poisoning of wildlife. Residual weed killers are probably the worst in this respect because of their very nature they leave a persistent plant toxic layer in the soil. Regular use of these can lead to a build up and the leaching of toxic chemicals down to the ground waters from which they can enter streams and watercourses 12