An important principle of ChemFree bio-holistic viticulture is the development and maintenance of good soil structure, fertility and biological activity. Sustainable ChemFree viticulture practices include the use of composting and the cultivation of plants that attract insects that are beneficial to the health of the vines. Sustainable practices in vineyards extend to actions that have seemingly little or nothing to do with the production of grapes such as providing areas for wildlife to prevent animals from eating the grapes and allowing weeds and wildflowers to grow between the vines. Some sustainable farmers may plough with horses. Sustainable wine making is a systems perspective of integration of the natural and human resources, involving environmental health, economic profitability, and social and economic equity. ChemFree weed control in vineyards requires preventing weed problems before they start. Cover crops planted in middles and mechanical and or biological (sheep, ducks etc) control of weeds in the vine row are key components of a ChemFree weed management program.
Weeds are not always weeds
The real and perceived status of plants as ‘weeds’ can vary significantly between vineyards and regions because of differences in soil, climate, vineyard age, management practices, end use of the crop and the philosophy of individual grape growers. For example, grasses are often encouraged in cool climate vineyards on fertile soils where their competition for nitrogen is used to reduce excess vine vigour. On naturally poor soils of some hot, dry regions however, summer grasses tend to be discouraged, because they compete for water and nutrients – major issues for some regions. Summer ground cover does however help reduce vineyard temperatures and dust.
Many agricultural weeds have been defined as such because of their negative impact in pasture and grain cropping systems, the dominant form of agriculture in Australia. Their impact, or role, in vineyards can be quite different. Because of these differences, it is important that grape growers assess the weed status of plants in their own particular situation. However, consideration of potential weed spread to neighbouring properties should always be taken into account. Your weed management should be prioritised by:
Impacts on your vineyard, and
Potential impacts on your neighbours.
Beneficial ‘weeds’
Some ‘weeds’ provide benefits of value to bio-holistic ChemFree vineyard systems, and these benefits need to be weighed against any negative characteristics of the weeds. Some benefits of weeds are listed below:
Soil protection - Most plants protect otherwise bare soil from the effects of sun, wind and rain.
Food source for beneficial insects - Many flowering plants produce pollen or nectar that is a useful food source for beneficial insects such as Trichogramma (a wasp parasite of lightbrown apple moth), hover flies and lacewing insects (predators of mealybugs, scales and other vine pests) and predatory mites (predators of pest mites on grapevines). Other plants, like thistles, support aphids which provide a food source for beneficial insects and help maintain populations of those beneficial species in the vineyard.
Nutrient recycling - Deep-rooted plants play a useful role in nutrient recycling by absorbing nutrients from lower in the soil profile and redistributing them when the plants decompose.
Weed suppression - heavy growth of some ‘weeds’ like grasses, can suppress the establishment and growth of less desirable weeds such as the spiky-seeded three-cornered jack.
Pre-planting weed management
Managing weeds before vines are planted, helps to reduce the weeds’ competitive pressure during the establishment phase of the new vines. It also helps to reduce the risk of vine damage resulting from post-planting weed control practices such as cultivation.
Pre-planting weed control is especially important where the ground is infested with perennial weeds like couch grass (Cynodon spp), Johnson grass (Sorghum halepense) and nutgrass (Cyperus rotundus). Weeds such as these, established amongst vines, are much more difficult to manage than those growing in open ground. Weeds in new vs established vineyards.
Good weed management is critical for newly planted vineyards, because of the relative inability of new vines to compete for light, water and nutrients. Vines are most susceptible to competition from weeds during their first three to four years of growth (Elmore & Donaldson 1999).
Inadequate weed management during this period can significantly delay the early growth and profitability of new vineyards. After this time, the vines’ larger root systems permit them to compete with weeds more strongly. Shade from the vine canopy also helps suppress weed growth under established vines.
Appropriate vineyard design. Eg: choice of irrigation system can influence weed development and weed management approaches.
Choice of appropriate management methods - use effective techniques that minimise negative impacts on the vineyard environment (eg. soil).
Monitoring - know where weeds are a problem and how effective the control strategies have been.
Rather than relying upon one or two methods of weed control, use any appropriate methods to deliver the best outcome. One reason to integrate several weed control methods into a weed management program is that generally, no one method can control all weeds, cost-effectively, all the time. This is because;
Some weeds are easier to control than others;
Some weeds are annual and some perennial;
Some are spread by cultivation, others by wind;
Some are avoided by grazing animals;
Some are very competitive against cover crops.
By combining weed control methods, grape growers can reduce the risk of particular weeds dominating the vineyard and causing major problems.
Total property weed management
Bio-holistic programs should take the whole property into account. This helps minimise the risk of the vineyard area being continually reinfested by weeds carried by wind or on machinery. Weed management needs to be integrated with overall vineyard management. Weeds, pests, diseases, soil, water and vines are all interrelated aspects of the vineyard system. Good planning and timely implementation are required for grape growers to maximise the benefits from their bio-holistic programs. Non-vineyard areas like irrigation channels need to be included in the weed management program.
Keep weed management objectives realistic
Weed management objectives need to be realistic and achievable if the programs are to have any chance of implementation, let alone success. For example, where curled dock (Rumex crispus) is considered undesirable, an objective to eradicate it from a vineyard within the short to medium term may be unrealistic, given that dock seed can remain viable in the soil for up to 80 years (Telewski and Zeevaart 2002). A more realistic objective would be to prevent further seed set of that weed. A grower's objectives and motivation in weed management also needs be considered.
Weed management techniques
Quarantine
Quarantine is used to minimise the introduction of weeds into the vineyard, and their spread between vineyard blocks. As a preventative measure, quarantine is very cost-effective, compared to the resource input required to suppress introduced weeds over the long-term. Ensure mulch and other materials obtained off-site are free of weeds. This approach also reduces the risk of undesirable chemical residues entering organic vineyards. When using the quarantine approach:
Restrict the movement of machinery, people and livestock onto and across the property, especially those coming from high-risk, weed-infested sites;
Clean machinery/equipment before it enters the vineyard, to remove weed seeds, bulbs, roots etc;
Take care in selecting clean sources of potted vines, mulch, raw materials for compost, or other materials that may be weed-infested;
Develop buffers such as windbreaks and surface water diversion, against wind and water-borne seed from adjacent properties.
Hygiene
Hygiene is a component of quarantine, and involves additional elements that reduce the spread of weeds within a vineyard. As well as the points listed above, vineyard managers should:
Prevent weed seed set wherever possible;
Avoid activity that spreads weeds vegetatively. Eg, avoid cultivating through areas infested with nutgrass, couch grass or other perennial weeds;
Destroy seed of noxious weeds by burning, deep burial etc. Grazing is not always a reliable technique, as the seed of many weeds germinates after passing through grazing animals (Govt. British Columbia 2002).
Monitoring
Monitoring is an important aspect of weed management. It helps grape growers to identify a site’s major weed issues and hotspots, select appropriate management techniques, and determine the best timing of treatments (eg. soon after germination to prevent weed establishment or at the start of flowering to prevent seed set). Monitoring also reveals the effectiveness of weed control techniques. This is necessary for fine-tuning of weed management programs.
For monitoring to be of value, it is important that weeds are identified correctly. Weed surveys and mapping are also a useful way to document a vineyard’s weed status for future reference. Surveys should be carried out at times appropriate to the particular vineyard situation, eg. on drip-irrigated sites a week or two after significant rainfall events, to detect widespread germination of summer weeds, or after autumn breaking rains for winter weed germination.
Competition
Weed growth can be suppressed by competition from other plants for water, light, nutrients and space. A simple weed risk formula applies to ChemFree bio-holistic vineyards like most other agricultural systems;
Bare soil = Weed problem!
In most ecosystems with adequate water resources, bare soil is unnatural, a sign of imbalance or disturbance. To counter this, many plants are adapted to colonise and cover bare soil very effectively. The result is that grape growers who attempt to maintain their system in a state of imbalance, that is, keep their vineyard soil bare, generally find themselves battling constantly against these colonising plants, or ‘weeds’.
In contrast, many weeds are poor competitors, and their establishment, growth or seed production can be greatly reduced by a reasonable level of competition from more desirable plants. Wherever possible, growers should design bare soil out of their vineyard management system.
Cover crops and green manures are commonly used in ChemFree viticulture to improve soil structure and fertility, and out-compete weeds in the inter-row area. Weed pressure is also reduced by the cultivation used to prepare seed-beds for these crops. The choice of appropriate crops will depend upon local climate, soil conditions and water availability. Mixtures of cereals and legumes are often the most competitive cover/green manure crop, but local expertise and experience should be used in choosing the right crop for each situation.
For effective weed suppression, green manure and cover crops need to be managed well so they cover the soil as quickly as possible to smother emerging weeds. Particular attention should be given to irrigation, nutrition and pre- and post-planting weed management, with such an implement as a flexible-tined finger harrow.
Another aspect of competition is that of allelopathy, which involves the suppression of seed germination or plant growth by chemical substances produced by another plant.These substances may be leached from the foliage or secreted from the roots of the growing plant, or released from the plant when it dies and decomposes. Many plants produce allelopathic substances (Rice 1984). Of the potential cover/green manure crops for use in ChemFree vineyards, barley and cereal rye are known to suppress numerous weed species and are considered to have the greatest allelopathic potential.
Mowing
Mowing is often used by organic grape growers to keep cover crops and weeds to a manageable height. It is a relatively fast operation that causes minimal soil disturbance, although soil compaction may become an issue where mowing is frequent.
The timing and height of mowing are important and can be manipulated to suit the grape grower’s objectives. Mowing during or before flowering of weeds will prevent seed production. High mowing (eg. 20cm) will reduce or prevent seed set in medium to tall weeds while allowing useful species, including non-grasses, to regenerate. Low mowing tends to favour grasses over many other desirable plants, because the regeneration point for grasses is low. For the same reason, low mowing is not effective against weeds with very low crowns, like capeweed and caltrop.
Mowing of cover crops or resident vegetation can be used to produce mulch material for weed suppression in the inter-row or vine-row areas. If mulch is desired, slasher mowers are preferable to mulchers (eg. flail mowers). The coarser material produced by slashers will break down more slowly and have a longer effective life as a mulch. Growers should consider a program of slashing alternate rows, allowing the uncut rows to provide habitat and food sources for beneficial in sects in the vineyard.
Grazing
Grazing has considerable potential for weed management in vineyards, and is in keeping with organic certification standards which encourage the incorporation of livestock into organic farming systems. In vineyards, sheep and geese are the most likely candidates because of their size and relative ease of management even goats if used at the right time. A side benefit of grazing is that useful nutrient recycling occurs through conversion of weeds into manure. Well-managed grazing livestock can also provide a useful income source.
Grazing needs to be managed to avoid damage to vine shoots. In well-established Australian organic vineyards that use winter grazing for weed control, the sheep are removed from the vineyard before budburst to prevent them from eating the new vine shoots.Grape growers using grazing for weed control need to address several management issues including:
A need for temporary fencing or a suitable alternative to control stock movement and avoid over-concentration in specific areas;
Protection from predators (eg. dogs, foxes & eagles);
Selective grazing (eg. geese prefer grass) that can lead to dominance of specific weeds.
Heat
Thermal weeding uses heat in various forms (radiant, flame, steam, hot water) to kill plant tissue. This technique has been researched and used for weed control for many years, but is generally economically effective only against small seedlings. For this reason, thermal weeding is most commonly used on row-crop seedbeds, to kill the new flush of weed seedlings before the crop germinates. It has however also been used in vineyards and orchards.
A benefit of thermal weeding is that it does not disturb the soil. Organisms below the soil surface are generally not affected, as the heat does not penetrate far into the soil. A disadvantage of thermal weeding is its high energy cost - it is usually based on fossil fuel such as diesel or bottled gas.
It is also a relatively slow operation to achieve a good weed kill. Also, flame weeders may create a fire risk, especially where there is dry ground cover or mulch. Research into thermal weeding continues, and new advances in technology will help make it a more economical and practical weed management option for organic grape growers.
Rolling
Weeds and cover crops may be flattened with a roller instead of being mown. Rolling leaves the plants largely intact, so they break down more slowly and create a longer-lasting mulch layer. The experimental roller pictured below is cheap to manufacture and maintain, and can be towed by a four-wheel ATV.
Mulching
Mulch inhibits weed growth and germination of weed seeds by blocking sunlight and light rainfall from reaching the soil surface. It also forms a physical barrier to weed growth. Almost any organic material can be used as mulch, with straw being commonly used in vineyards. Grape marc and composted green municipal waste is also used. Other materials include shredded paper, wet paper pulp (sprayed on) and jute matting.
The correct depth of mulch is important. Weeds will not be suppressed effectively if the mulch is too thin, and overly thick mulch can shed sprinkler water and rainfall away from the vine row. Some local experimentation may be required to determine the best mulch depth for each situation, but as a general guide, approximately 20cm of straw mulch is recommended, while only 7.5cm – 10cm of composted green waste mulch is required (Buckerfield).
Mulching is commonly used for weed control in the vine row and is particularly useful on stony soils where under-vine cultivation is difficult or impossible. Good reasons for managing in-row weeds with organic mulch include:
Some mulches (eg. partly composted green waste) are a useful source of nutrients;
The mulch adds organic matter to the soil;
Vine roots concentrated directly under the vine are protected from excessive heat;
Mulching helps avoid vine damage from cultivation;
Vine trunks, sprinklers and irrigation tubing make cultivation and mowing difficult in the vine row.
Mulches do have some disadvantages that include:
Partly decomposed mulch may create an ideal seedbed for weeds;
Mulch may harbour pests such as snails; (although weeder ducks can work here)
It can be difficult to manage weeds at the mulch/inter-row interface without disturbing the mulch (steam weeding is an option).
The need for reapplication of organic mulches, possibly annually, has to be considered when costing this method of weed management. Also, as most organic mulch material is bulky, the cost of transport and handling needs to be considered.
Another consideration relating to mulch materials is their influence on soil microbial communities. 'Soft' materials such as straw or slashed cover crops are likely to favour bacterial decomposers, while fungi are more likely to be encouraged by 'hard' materials such as chipped wood. Growers who aim to fine-tune their soil management may need to take this into account.
Mulch costs may be reduced by growing mulch material on-site as inter-row green manures or cover crops. The mowing/mulching operation may be performed in a single pass with a side-throw mower that delivers the material directly to the under-vine bank. This is a good approach for ChemFree vineyards, as it reduces the need for external inputs. It also reduces the risk of bringing unwanted weeds into the vineyard, in contaminated mulch material.
Synthetic weed mat effectively suppresses some weeds, and a temporary mulch of black plastic may be used to kill patches of difficult weeds including couch grass, by starving them of water and sunlight. This technique does not need the hot conditions required for solarisation, but has to be applied over months rather than weeks. Disposal of these materials is an environmental issue that ChemFree growers would need to consider. Also, their use may be restricted by organic certification organisations.
Soil modification
Different plants are adapted to different soil conditions like high or low pH, salinity, fertility, moisture content, compaction and so on. Because of this, the presence, dominance or quality of growth of particular plants, including weeds, may indicate to some degree, the underlying soil conditions. A predominance of wireweed or knotweed (Polygonum aviculare) is indicative of compacted soil, and is commonly found on vineyard headlands.
Awareness of this relationship between weeds and soil gives vineyard managers some opportunity to address their weed issues by modifying their soil conditions. In the long-term, this may be more cost-effective than tackling the weeds directly. Weeds are not always 100% reliable as indicators of specific soil conditions because, for example:
Some weed species are tolerant of a wide range of soil conditions;
Some are sensitive to a number of environmental conditions;
Some species develop localised ‘ecotypes’ that differ in their adaptation to specific conditions.
For this reason, care should be exercised when using weeds as soil indicators. Communities of weeds, rather than individual species, are likely to give more reliable indications of soil conditions. Growers should compare several information sources and combine them with their own observations as a basis for interpretation of the soil conditions indicated by their weed communities.
Mechanical cultivation
Cultivation destroys or buries weeds, disrupting their growth and preventing seed set. Most forms of cultivation are very disruptive to soil structure and to soil organisms. Cultivation can also spread seeds, tubers and rhizomes of noxious weeds, is relatively energy-expensive and increases the risk of soil compaction. Despite these costs, cultivation is common practice in organic viticulture. Standard tools such as disc or chisel/tine ploughs are generally used to cultivate the vineyard inter-row area. The undervine area is cultivated with specialised equipment. These tools are mounted on manually or automatically-operated retractable arms, so they can be moved around vines and irrigation risers. With this equipment, experienced operators can clean vine rows of weeds relatively quickly, with little if any damage to the vines.
Some growers use these or other tools to control annual weeds with the scrape-off/throw-on strategy. Soil is repeatedly shuffled on and off the under-vine area to destroy weeds where the soil is removed, and smother those where the soil is dumped. In hot dry climates, under bare soil, grapevine roots usually avoid the top 100mm or so of soil, so the root system will be largely unaffected by shallow cultivation. In cooler regions, or where mulch has been applied, shallow roots will develop and these will be destroyed by undervine cultivation.
Solarisation
Solarisation involves the destruction of plants and seeds by the solar heat trapped when soil is covered by clear plastic sheeting during hot weather. While this technique is more commonly used to kill disease organisms in the soil, it is also effective against many weeds and their seeds.
However, it is generally not effective against weeds with deep tubers or rhizomes, like Johnson grass. Effective solarisation requires good movement of heat into the soil. This is aided by high levels of soil moisture, so, if necessary, the soil should be irrigated before the plastic is laid down. Air gaps between the plastic and soil should be minimised as they inhibit heat transfer into the soil. To prevent the plastic being lifted by wind, and to reduce the leakage of heat, the edges of the sheet should be buried.
Solarisation for at least four weeks is likely to be needed for effective weed kill. This will vary according to the quality of plastic sheet used, the prevailing temperatures and weed species present. Winter weeds are likely to be less tolerant of high temperatures than summer weeds, and therefore more strongly affected by solarisation.
To avoid reinfestation of treated areas with weeds, the soil should be mulched or sown to a green manure/cover crop as soon as possible after removal of the plastic. Avoid bare soil.
Hand cultivation
ChemFree grape growers often do some hand weeding to remove weeds from around young vines or weeds that are too close to vine trunks to be removed by undervine cultivators or mowers. Although hand weeding is time-consuming, and therefore expensive, it is effective and gives growers an opportunity to observe their soil, vines and vineyard closely.
Timing is critical
In some situations, the timing of weed control treatments in relation to the weeds’ developmental stage or weather conditions is critical - a few days can make the difference between success and failure. Weed management actions should be prioritised, scheduled and performed at the optimum timing for best results.
If management of a specific weed relies upon the prevention of seed set, then control treatments must be given adequate priority and applied before, or during flowering. Whenever weeds are allowed to produce a new generation of seed, the problems caused by those weeds will be perpetuated, as will the need for ongoing control. For example, a single plant of blackberry nightshade (Solanum nigrum) can produce over 170,000 seeds (Whittet 1968).
Similarly, cultivations to disrupt weed seedlings or to chop the rhizomes of perennial weeds will be more effective if followed by hot, dry weather rather than cool, wet weather. Priority should therefore be given to timing such cultivation according to the prevailing weather conditions.
Try something different
Ongoing problems with weeds are an indication that the current approach to weed management is not working. In this case, vineyard managers should try different techniques or different combinations of techniques in an attempt to find a more cost-effective and long-term solution to those weed problems.
Innovation and perseverance are necessary ingredients for successful weed management.
