Yarrow identification and control

Yarrow Achellia millefolium

A perennial broad-leaf weed, commonly found in lawns and very tolerant of drought conditions.

Appearance

Yarrow has lanceolate shaped leaves that are significantly longer than they are wide and gradually tapering towards the end. They have a fine, fern-like appearance.

If left unmown, flower heads made up of dense clusters of white or pale-yellow flowers are produced between June and September.

Growth habit

Yarrow has a dense, fibrous root system made up of strong underground runners that helps it to spread.  Roots can penetrate to a depth of 20 cm enabling it to withstand drought conditions.

Conditions that favour its development

Yarrow will do well in dry, nutrient poor soils, where it can easily compete against a weakened grass sward.

Cultural control

Maintaining favourable growing conditions for the turf will help to minimise invasion of this weed.

• Ensure that grass plants receive adequate nutrition, applying a suitable lawn fertiliser at regular intervals throughout the growing season to create a dense, healthy sward to minimise spaces for weed invasion and to maintain competition.
• Irrigate the turf, as required, to maintain sward health.
• Aerating regularly will keep the surface open to effective irrigation and rainfall and encourage the natural breakdown of organic matter which can be prone to drying out. Do not be tempted to over-water as this will weaken the sward giving opportunity for invasion by other weeds.
• Mowing regularly at an appropriate height will prevent the formation of flower heads and seeds.

Small plants can be weeded by hand but care must be taken to remove the roots

Chemical control

Chemical control of Yarrow is difficult because of the waxy nature of its leaves which can be hard to wet. More than one application of selective weedkiller will almost always be required.

Always apply when the weed is actively growing, usually between April and October. Repeat if necessary.