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LONG-term weed management can be achieved by the appropriate use of required methods along with other land management practices like re-vegetation which is also referred as the integrated weed management (IWM).
The aim to incorporate cost effective, practical methods which help in reducing the reliance on herbicides. These reinforce the goal of achieving long-term weed control without damaging the environment. It requires planning based on the knowledge of weed’s life-cycle, control methods, soil, climate and other vegetation. It also includes regular monitoring and actions.
A common example of the IWM is the use of fire or slashing to destroy large weeds followed by herbicide applications to control the seedlings and then hand removal of plants before re-seeding. This may be complemented with either regeneration or re-vegetation with the desirable species. An IWM approach means less herbicide and follow up time.
The control categories considered in the IWM herbicides are:
Herbicides: These are chemicals applied to kill plants and are a useful tool in the management of weeds. These are poisons therefore, the risks associated with the preparation, use, handling and storage need to be understood. The aim is to get the right herbicide at the required dose using appropriate method at a correct time and delivered in a safer way.
HAND CONTROL: Hand or manual methods offer alternatives to herbicide treatments, particularly in sensitive areas. They are a part of an integrated approach, especially for the follow-up control of herbicides. The techniques are labour-intensive and generally not suited to extensive infestation treatments. These get close to the weed thus improving identification skills in understanding the weed’s biology.
Hand pulling: Hand pulling is useful for isolated occurrences of seedlings or other small, soft, non-bulbous weeds. It is best undertaken when soil is moist and loose with minimum disturbance. Remove the seeds or fruit and bag them for disposal.
DIGGING: Digging, hoeing or grubbing out weeds can be effective for isolated occurrences and are useful follow-up techniques. With practice, gentle digging and grubbing out of weeds will keep soil disturbance to a minimum. However, this is not always the best method for species with extensive tuber, rhizome or root systems. For example, larger woody weeds may be more effectively treated with herbicides, which will cause minimal soil disturbance compared with digging out deep or extensive root systems.
MECHANICAL: Machines, from lawn-mowers to earth-moving equipment can play an important role in weed management. The use of machinery risks site disturbance and the potential to spread weeds as a consequence of plant material attaching to machinery and re-depositing elsewhere. Good planning to minimize site disturbance and restore treated sites is essential, as is the machinery hygiene.
SLASHING AND MOWING: Slashing and mowing may be valid components depending on the weed being treated. These will not eradicate but can stress weeds, providing desirable vegetation with a competitive edge, leaving more susceptible to bio-control agents and also preventing or reducing seed production. Proper timing is required for optimal results based on the growth stage of weed species and of desirable vegetation. Mowing should be carried out at not so early or not very late. It should be at the time when desirable plants are dormant. The idea is to exploit differences in the growth habits of grassy weeds and desirable grass species.
BULLDOZERS AND TRACTORS: Heavy earth moving equipment is effective in severe infestations of larger woody weeds. Bulldozers are important in dealing with large infestations of prickle bush species including prickly acacia, mesquite (Prosopis spp.) and parkinsonia and allow treatments such as blade ploughing, chain pulling, dozer pushing and stick-raking.
GROOMING: Tractors and earth-moving equipment fitted with specialized ‘grooming’ arms effectively treat large infestations of woody weeds in hard places. The devices shred plant material down to ground level, reducing biomass.
CULTIVATION: Cultivation defined as working the soil with implements is often used in cropping situations to prepare the soil for sowing and to destroy competing plants. Its use is diminishing to conserve soil with herbicides to control weeds. Cultivation works by cutting, uprooting and burying shallow rooted plants. It has a limited application because the disturbance caused would only serve to stimulate weed growth and help spread seeds and other propagules whilst destroying native vegetation.
MULCH AND SMOTHERING: Mulch may help control weeds by excluding light from the soil surface, reducing temperature variations and by physically impeding growth. Many forms of vegetative material including bark, wood chips or mats made from vegetative material are used, as are synthetic materials such as black plastic sheeting or mineral aggregates.
The application of mulches outside the garden or horticultural environment is probably limited, except perhaps for highly disturbed or degraded areas where no indigenous species regeneration will be affected by the mulch, or around seedlings planted as part of re-vegetation work.
It is important to secure material used for mulching to prevent them from being torn (introducing gaps), blown or washed away. Mulching may assist re-vegetation establish by suppressing weeds around young native plants and improving retention of soil moisture. Organic mulches such as hay or straw may also contain weed seeds and can temporarily tie up nitrogen in the soil.
SOLARIZATION: This employs sheeting, usually black or clear plastic to cover weeds and allow the sun’s energy to raise temperatures under the sheeting to an extent that weeds and their seeds are destroyed. It can be useful to treat small infestations of tenacious grass and herbaceous and is best used in warmer months and in locations with open and sunny aspects.
Black plastic sheeting has been used to control some aquatic weeds, for example Lagarosiphon major, in still water conditions. It is also a method to sterilize weeds to be disposed of, by accelerating composting and subjecting the material to high temperatures. This can eliminate the need to take material off-site and reduces the risk of inadvertently aiding weed spread.
COMPETITION: The best way to keep an area free of weeds is to have a cover of desirable vegetation comprised of native species, indigenous to the area. In agricultural settings, pasture species might be desirable. The objective of most site plans is to restore the original ecosystem by establishing local native species to replace the weeds.
REGENERATION: Native species can be allowed to regenerate from seed stored in the soil-seed bank or held in remnant native canopy species. In these circumstances weed control should be paced so that gaps are not created for fresh invasion.
The main principles of this method are to work from minimally disturbed sites towards the most infested areas; minimize disturbance to soil; allow the rate of native plant regeneration to dictate the rate of weed removal.
MANIPULATION: Seed bank exists or the plant canopy may be exploited by burning to stimulate germination. This should only be applied where monitoring confirms the presence of a substantial seed resource. It would not be appropriate in rainforest ecosystems.
SOWING: Direct seeding requires germination knowledge for giving plants an opportunity to establish in the shortest time, reducing the chances of reinvasion by weeds. Many seeds require some form of pre-treatment (e.g., scarification, heat or smoke to stimulate germination. Timing of the sowing to take advantage of reliable rainfall or low seed predator activity may help in maximizing the chances of establishment.
PLANTING SEEDLINGS: Planting native seedlings is a labour-intensive and expensive task but achieves higher establishment rates. Planting should be carried out at a time when plants get the best chance of establishment, and temporary protection from grazing may be required. Mulch may assist in suppressing weeds by retaining soil moisture whilst seedlings become established. Selection and re-vegetation timing are complex matters needing advice from experts.
FIRE: Fire is relevant long-term management of weeds. Areas left bare by fire are susceptible to erosion and weed invasions. It is advisable to restrict the area that requires follow-up after planned fires to manageable levels. In areas with vegetation, fire should not be used in frequent succession on the same site as it may favour weedy species. Moreover, the risks to people, fauna and property need be understood and managed and appropriate measures like permission should be obtained before the fire is used.
The four aspects need to be considered are flame weeding and steaming, flame weeding, steam weeding and biological control.
