Pre-plant applications

• A total cover spray before planting is essential to ensure that the area is weed-free for as long as possible, giving young trees more time to establish themselves before riskier, and costly weed control/management operations have to be used.
• Timing and quality of the operation is critical to ensure effectiveness.

Post-plant applications

• The focus is to eradicate all competing weeds within ~25cm around the tree for the initial zero to one/zero to three-year period with a focus on the AIS. Inter-row weeding should then not be more than 25%, specifically targeting weeds that have reached a height of 50cm as these compete for nutrients and water.

Eucalyptus and wattle compartments under 12 months and pine compartments under three years are more susceptible to weeds and therefore need to be prioritised.

Research shows that the removal of weeds, thus competition for resources, has significant benefits:

• Eucalyptus trees kept free from weed competition have a substantially higher yield.
• Pine trees have an improved survival if kept weed-free for the first three months. Weeding thereafter has no significant growth benefit but does have advantages such as reduced fire fuel loads and airflow in frost-prone areas.

The weed spectrum present will dictate the control methods used. As a result the following weed characteristics should be identified:

• The presence of broadleaf weeds or grasses and the ratio of each.
• Whether the weed species are annual or perennials and the ratio of each.
• Life cycle – the aim is to eliminate weeds, not wound them. This means knowing their life cycle and targeting the growth stage where they are most susceptible to pesticide control measures. This minimises the amount of herbicide required and improves the productivity of the application method.
• Presence of AIS.
• Presence of invasive indigenous species.
• When conducting spraying operations, weeds should be targeted as young as possible, whilst at the same time, ensuring that there is an adequate weed flush, and in some cases, sufficient leaf material to absorb the herbicide.

Threshold levels identify when weed control becomes cost effective and necessary. Threshold levels are dependent on numerous factors, and can therefore differ for the same species of weed between compartments as well as land-use types. It is important to know the threshold level for each species and compartment.

Factors impacting threshold level:

Age of tree species planted threshold levels will be lower for younger trees as they are more susceptible to weed competition.

Species of tree and end use – Pines are susceptible to competition from weeds for a longer period than Eucalyptus and wattle, so will have longer and lower threshold levels. It should be noted that weed susceptibility also varies between different genera and hybrids. Knowledge of the trees’ response to weed competition is crucial.

Species of weed(s) – Physical and behavioural characteristics of individual weed species will dictate the threat level they pose, thus where the threshold levels are set.

• The presence of certain species identified as posing specific threats to trees, or biodiversity in general, should alone be enough to initiate control measures.
• Other species will be tolerated at low levels, but once they reach a certain point, control measures must be initiated. Continual monitoring will be required if their presence is noted.

Damage incurred – The type of damage incurred to the tree, or natural ecosystem, will dictate where threshold levels are set and the extent of control necessary.

Cost of control product can also be an inhibiting factor and should always be considered and weighed against the potential cost of damage incurred without weed control.

Cost of application method – There are significant differences in the financial and time costs of different application methods. These need to be considered when determining threshold levels, as well as the costs of additional monitoring, if weeds are left untreated.

There are several different weed control methods available. These include cultural controls, biological controls and herbicide controls. In accordance with good agricultural practices and the sustainable Integrated Pest Management (IPM) philosophies applied by the South African forestry industry, cultural and biological methods should first be considered. If these methods found to be non-viable, then herbicide control can be implemented as a last resort. Selection of appropriate methods of control shall be based on the following criteria:

• Species to be controlled
• Size of target plants
• Density of stand
• Accessibility of terrain
• Environmental safety
• Presence of desirable vegetation
• Presence of obstructive vegetation. (conservation areas)
• Cost of application

Refer to SOP introducing IPM

Some considerations when selecting the type of herbicide control measures include:

• Ensure it is on the TIPWG approved pesticide list. These are SA government registered and approved (sometimes with conditions for use) by the Forest Stewardship Council® (FSC®). Refer to TIPWG APL.
• Correct handling and use. Refer to SOP: Handling and Application.
• Correct storage and transport. Refer to SOP: Storage and Transport.
• When using selective herbicides, this often requires planning and budgeting for potential and additional operations.

In forestry, there are two primary weed control application methods: knapsack sprayer (refer to SOP knapsack) and tractor with spray cart (refer to SOP mechanical sprayer). Each has benefits and limitations. It is important to know these before selecting the method.