Weed of the Week: Yarrow (Achilles millefolium)

Weed of the Week: yarrow (Achilles millefolium)

By Laurence Gale

What is a weed? By definition a weed is a plant that is growing in the wrong place. Weeds take valuable space, water, sunlight and nutrients that may otherwise be accessible to important crops, in our case turf grasses. Weeds not only compete for these resources they can disfigure and cause problems to playing surfaces.

Weeds are very good competitors and take advantage of any opportunities to colonise turf situations, particularly when the sward is under stress and weak, leaving bare soil areas for weeds to populate. Weeds have many mechanisms and characteristics that enable them to do this, having thick waxy cuticle leaves that can be resistant to some chemicals, fast reproduction methods, the ability to reseed in 6 week cycles and deep tap roots enabling the weed to survive in compacted dry ground conditions.

Weeds have one of three life cycles: annual; biennial or perennial.

• Annual weeds: Live for a single season. These weeds germinate from seed in the spring or summer, flower and then die.
• Biennial weeds: Live for two seasons. During the first growing season, these weeds remain in a vegetative stage and, in the following year, produce flowers, set seed and die.
• Perennial weeds: Live for multiple seasons and flower more than once. Perennial structures (rhizomes, stolons, crowns, entire plants or roots) survive from year to year.

Some weeds may be harmful to the environment or noxious to your regional ecology. For example Japanese Knotweed (Fallopia Japonica) is fast becoming a major weed problem on road side verges and urban landscape areas, a very difficult weed to eradicate. It is very important to recognise weeds and seek effective controls methods to eradicate them from our facilities.

Weeds can also be used as an indicator of soil conditions. For example, knotweed and plantains both indicate soil compaction because they can maintain adequate root respiration at lower oxygen diffusion levels than other plants. Different weeds tolerate different soil conditions, some are alkaline loving and others acid loving. Getting to understand and recognise the physiology of these plants will help you become better turfgrass managers.

This weeks weed is: Achilles millefolium (common yarrow)

Scientific name Family Life cycle	Achilles millefolium . Asteraceae, formerly Compositae Perennial
Form / Appearance	The leaves are lanceolate and divided into narrow segments, appearing fern-like. The leaves of yarrow are strongly scented. Yarrow flowers are rarely seen in mowed situations.
Roots	Yarrow has a very fibrous root system that consists of many rhizomes which play a major role in the plant's ability to establish itself in turf and make the plant difficult to eradicate.
Flowers	White or yellow flowers are formed at the ends of stems in dense, flat clusters. Flowering occurs in June to October.
Leaves	Leaves on mature plants are finely dissected, giving them a feathery appearance, and resemble a fern.
Reproductive method	Yarrow reproduces itself from seed and Rhizome development.
Habitat	Yarrow is a drought tolerant perennial that can endure dry, impoverished / infertile sandy soils and survive with little or no maintenance. Yarrow's main growth period is from April through to September. Yarrow is a good indicator of infertile soil conditions.
Miscellaneous info	Yarrow is also known as milfoil, thousand leaf or woundwort. Yarrow is used as medicinal remedies by herbalists, it has been valued since ancient times for its ability to stop bleeding, hence its nickname "nosebleed." Today, yarrow is valued for its ability to fight off colds and flu. Yarrow is a tough, durable and aromatic weed.
Cultural Control	Yarrow can be mechanically or physically removed. Care should be taken to assure that all roots are thoroughly removed. Close mowing prevents seed head formation, whilst maintaining a dense sward will deter or prevent yarrow from establishing. Good soil fertility is essential, maintaining a soil pH of 6.5 to 7.
Chemical Control	Apply selective broadleaf herbicides when plant growth is active. There are a number of products available for controlling broad leaf weeds in established turf. These chemicals are best used when the weeds are actively growing, usually between April-October. Tritox (Contains 178g/L (16.2%w/w) MCPA 54.g/L(4.9%w/w) mecoprop-p and 15g/L (1.4%w/w) dicamba and potassium salts. Scotts. Intrepid 2. (Contains 20.8g/L dicamba,166g/L dichlorprop-p ans 166.5g/L MCPA). Scotts. Greenor. (Contains: 40g/L fluroxypyr, 20g/L clopyralid and 200g/L MCPA). Rigby Taylor. Bastion T. (Contains: 72g/L fluroxypyr and 300g/L mecoprop-p ). Rigby Taylor. Dormone (Contains 465g/L2,4-D(38.1%w/w) as the diethanolamine salt). A herbicide which can be used near water. Bayer Environmental Science. Supertox 30 (Contains 95g/L (8.8%w/w) mecoprop-p and 93.5g/L(8.7%w/w) as the diethanolamine salts). Bayer Environmental Science. These herbicides are usually applied as a liquid using watering cans, knapsack sprayers and vehicle mounted sprayers. Ensure you follow manufacturer's directions, health & safety and product data sheets, and comply with COSHH regulations, when using these chemicals. Herbicides are an effective tool where high quality turf is desired. However, they must be applied with care and accuracy and in the context of a good overall turf management program. Before using any herbicide, carefully review the label for conditions of use including rates, methods of application, and precautions. Never use an herbicide in any manner contrary to its label and be sure that the herbicide will not injure the turfgrass species