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Weed control in plantations

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Weed control is probably the most important management component to get right when establishing farm forestry plantations. The importance of weed control cannot be emphasised enough.

The first three steps to successful tree establishment are:

Weed control, WEED CONTROL and WEED CONTROL!!

Most commonly weed control in farm plantations is conducted with the use of chemicals, which are efficient and effective. This is not to say that for best results, an integrated approach to weed control is desirable. This may include the use of mulching around trees, slashing and even grazing when the plantation matures enough.

Weed control prior to planting

Before seedlings are to be planted it is imperative to remove any weeds on rip/mounds. Sites that are rip/mounded may already be weed free and a pre-plant weedicide application may not be necessary. If there are any weeds on rip/mound lines, the quick and easy method would be to apply broad spectrum herbicide, such as knockdown foliar sprays.

Application rates vary as to the directions on the label. In smaller plantations, it may be possible to remove rough weeds along rip/mounds through physical removal with mattocks and other like tools. It is generally only necessary to control weeds on rip/mounds and not the areas in between. Exceptions include cases where noxious weeds such as Serrated Tussock are present at the site or where woody weeds like Blackberry persist.

Serrated Tussock shows resistance to a number of herbicides and its control requires hard work and persistence over a number of years. Where plantations are strategically placed for weed control functions, the formation of consistent canopy closure can potentially clear the direct area of infestation. At the least, plantation canopy closure can retard seed set from weeds amongst the forest. Plantations to smother weed infestations may therefore only require herbicide application and the like early in the plantation's development.

Woody weeds are best removed by cutting the stem or stems at the base of the plant, then painting the fresh stumps with herbicide. Ensure you choose the right herbicide for the specific woody weeds that you are targeting.

Granular herbicide application in Pinus radiata plantations:

Granular herbicides such as ‘Forest Mix’ can be applied around individual trees for a residual weed control effect. This herbicide requires application with use of a ‘Weed-a-metre’, which is a
hand-held device with a simple trigger, delivering a measured dose. ‘Weed-a-metres’ can be hired through STFFN. Application should be conducted at least 4 weeks after planting. By this time, pines would have settled in, soil temperature should still be low and moisture ample. Granular herbicides should not be used when soil temperatures are rising and soil moisture is limiting as this may kill individuals of the plantation.

On-going weed control

In most instances plantations will require some form of on-going weed control. Now that trees are in the ground, broad-acre herbicide application will generally not be acceptable. Some forestry species
however are resistant to a few herbicides, thus over-spraying may be possible. In many instances the use of herbicide will require application with use of shields sprays and the like, to help minimise contact with establishing trees.

In some instances, particularly for smaller plantation owners, mulch application around freshly planted trees can have persisting weed control effects. Mulching trees will also add organic matter to the soil and help retain soil moisture.

Slashing can be used in plantations, especially in between rows. Slashing is most applicable for weed control in the greater area of plantations, rather than close around trees. Regularly slashed belts and areas amongst plantations can also be incorporated into fire risk management practices.

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