Mechanical Weed Control in Organic Orchards

Weed control in orchards is vital where high quality fruit production is required.  Modern apple rootstocks do not compete well against weeds so yield suffers where weeds are not controlled.  Because artificial fertilizers are not permitted in organic systems, good tree nutrition is much more difficult and any competing vegetation represents a significant challenge to the apple trees.   A wide range of herbicides is available for weed control in  conventional orchards but these are banned in organic systems.

There is a wide range of alternative systems which can be used; permeable mulches, heat (flame or steam) and mechanical cultivation.  No system offers a perfect solution.  Mulches are cheap to buy but time consuming to set up and have to be continually maintained and occasionally hand weeded. Heat equipment and soil inversion equipment are expensive to buy but cheap to run.

Heat technology does not control weeds where the growing points are below the ground surface (particularly grasses) and cultivation can promote some rhizomatous weeds: the root structures are being chopped up into small pieces each of which then grows.  So there is no perfect solution.  At Loughgall the soil rotivator system has been selected as more environmentally friendly than the burner system.

Rubber cutting head

The cutting blades under the cover spin according to the revs of the engine and the weight of the arm presses the blades into the ground.  The ground and plants are macerated.  The rubber head prevents damage to the tree and post.  The more often the soil is worked the more friable and weed free it becomes.

Soil after being worked several times

At Loughgall the system is being used in the organic orchard.  Here the grass clover sward is five years old and has been mown regularly.  The first passes with the cultivator proved very difficult due to the thick mat of the sward  resisting the blades and several passes were required to achieve the desired level of plant destruction.

The thick mat of vegetation to be mulched

The intention is to use the cultivator twice a year when the soil is relatively dry (and earthworm populations will be deeper under ground).  Vegetation under the tree canopy will be buried as will the cut grass clippings which  will be deposited under the trees.  The process will reduce plant competition and improve the rate of nitrogen release from the clippings to the soil.