Weed Control in Turf and Lawn

Introduction

Consider any unwanted plant in turf to be a weed.

Weeds are opportunistic and are virtually impossible to eliminate from turf. An appropriate weed control program limits weed infestations rather than attempting to eliminate them entirely. Weeds will soon invade weak stands of turf that lack density. In some situations, extremely competitive weeds can invade dense turf grass. The only effective approach to control weeds in turfgrass is to combine chemical weed control with an appropriate Turf Grass Management program directed at improving turf grass density and vigour appropriate Turf Grass Management includes appropriate mowing, watering, fertilizing and cultivation.

To combat weeds effectively, you must be able to identify them and understand their life cycles

Weed types
Turf grass weeds are generally classified as either grasses or broadleaves.

Grasses
These weeds are distinctive in that grasses are monocots. They have leaves with parallel veins and only one seed leaf in a developing seedling.

Broadleaf weeds
Broadleaf weeds are dicots they have a netted leaf vein pattern and two seed leaves on a seedling plant.

Sedges

Sedge is neither a grass nor a broadleaf they are often found growing on waterlogged acid soils or soils of poor fertility. Yellow nut sedge is the most prominent weed in this group. It has a grass like appearance with a distinct triangular stem, a deeply keeled midrib and no collar or ligule.

Turfgrass weeds are further classified according to their life cycle.

Weed life cycles

All weeds go through a cycle of seed germination, foliar and root growth, maturity and flowering, and seed development. You must understand weed life cycles because the effectiveness of herbicides depends on the stage of growth of a particular weed. For example, pre-emergence herbicides are effective only when applied before weed seeds germinate in the spring or autumn. Post emergence herbicides are most commonly applied on weeds found in turf, they are however much more effective when applied to weeds in a juvenile vegetative stage of growth rather than at a mature flowering stage of growth. If post emergence herbicides are applied to mature weeds, applications should be made in spring or early summer preferably when the temperatures exceed 20 degrees centigrade.

Winter annuals

Plants that live for one year only. Seed germinates in the autumn, the weed matures through the winter, sets seed and dies in the spring.

Summer annuals
Plants that live for one year only. Seed germinates in the late spring and early summer, the weed matures very rapidly in the summer and sets seed and dies in the autumn.

Winter perennials
Plants that live for several years putting on most of their growth in the winter months flowering and setting seed in the late winter or early in spring.

Summer perennials
Plants live for several years, which put on most of their growth during the summer months, they mostly flower and set seed in the summer or autumn

Biennials
Plants that live for two years, which put on most of their grow during the first summer, they tend to flower and set seed then die in the second summer.

Checklist for effective weed control
Identify the weed and understand its life cycle. Then answer the questions below:

Is the weed causing an economic or aesthetic loss that cannot be tolerated?

Can the weed be reduced to an acceptable population through good management practices alone?

If the weed is not controlled now, will it be more difficult to control in the future?

Are there herbicides that can effectively limit the growth of the weed, and can the herbicide be safely used without harming other plants or the environment?

Do I have the knowledge and equipment to safely handle, apply and store herbicides?

If possible determine the cause of the weed problem and design a management program to increase turfgrass competition and reduce weed competition.

Correct obvious major problems such as, poor soil fertility, soil compaction, traffic patterns and poor drainage that may be causing the weed problem.

When needed, safely apply herbicides so that weeds may be controlled and turf may resume a competitive density.

Cultural weed control

The basic principle involved in cultural weed control is to grow a stand of grass that is dense and competitive enough to prevent weed invision.

Weeds are not the cause of poor turf, but rather the result of poor Turf Grass Management practices.

Weeds require light, water and nutrients to grow. As turf loses density, light will penetrate the canopy and cause weed seeds at the soil surface to germinate. Once germinated, weeds can develop rapidly, especially if the turf continues to decline.
Weeds will probably receive sufficient light to develop if one can see bare soil when looking straight down on a stand of grass. Good Turf Grass Management practices that discourage turf weeds include proper mowing, watering, fertilizing, thatch control and cultivation. Using locally adapted turf grasses and establishing them during the correct season of the year can reduce the opportunity for weed invasion.

Mowing
To prevent weed germination, mow frequently at the tallest recommended mowing height. Weeds germinate rapidly when turf is scalped, by mowing too short or when it is not mowed frequently enough. Both mistakes decrease turf density and cause an open canopy that favours weed invasion. Experts recommend a range of mowing heights to meet specific turf activities. Lower mowing heights require more intensive Turf Grass Management. Each mowing should not remove more than one third of the total leaf height. Annual grassy weeds are especially a problem on turf that lack density as the result of poor mowing.

Soil Fertility
Areas that receive chemical weed control but no application of a balanced fertilizer are probably being mismanaged. Even in low- maintenance situations, the first defence against weeds is dense turf. For cool-season grasses (Bent, perennial rye, fescue), apply a high nitrogen, high potassium balanced fertilizer in the autumn. For warm-season grasses, (Cynodon dactylon, Pennisetum clandestinum) apply it in the summer. Additional fertilizing with a balanced lawn fertilizer should be applied during the growing season to provide adequate growth and density with less attention given to turfgrass colour. On cool-season grasses avoid heavy applications of high nitrogen fertilizer in the spring, which will encourage excessive vertical leaf growth, bringing with it a greater chance for fungal diseases and insect pest attack.

Establishment
Weeds can prevent the establishment of turf grasses at certain times of the year, late summer and early autumn are preferred for establishment of cool-season grasses. Cool-season turf grasses that have germinated by early March will not be affected by summer weeds and will usually establish a competitive stand of grass before winter annuals become a problem.

Thatch and cultivation
These have a dual effect in terms of weed control. Weed seeds below a thatch layer lack the necessary light for germination, so weed seeds generally do not germinate in the thatch layer or when they do usually die because of the poor environment for seedling development in thatch. In this respect, thatch provides some degree of weed suppression. On the other hand, thatch can cause turf decline by harbouring disease causing pathogens, reducing water infiltration and tying up pesticides and fertilizers. Power raking and verticutting are typically used to remove thatch.

Soil compaction
Soil compaction from traffic and tight soils will often decrease turf competition in favour of some weeds, especially Eluesine indica (Goose grass). Two ways to fix the problem are coring and slicing and the top dressing with sand. These procedures improve the soil surface and the growing environment for turfgrass.

Chemical weed control
The appropriate application of herbicides can dramatically reduce turfgrass weed populations in a short period of time. A combination of their cost effectiveness and simplicity of use often makes herbicides the primary means of weed control with little attention given to other weed reduction measures. Remember, herbicides are only one facet of the total weed control puzzle. Effective long-term weed control and a reduction of pesticides in the environment will be achieved only when an effective cultural weed control program has been implemented.

Types of herbicides
There are two general types of herbicides - selective and non-selective.

Selective herbicides kill only the target weed species, leaving the turfgrass unharmed.
Selective herbicides are further divided into their type of application. Pe-emergence herbicides are applied before the emergence of a weed. Post emergence herbicides are applied after a weed has emerged; they are generally applied to weed foliage.

Non-selective herbicides kill all plants they contact. (Glyphosate)

Michael Hickman
06.10.05

Ecoman Sports Turf and Lawn Expert

I have considerable experience with establishing and managing both warm season as well as cool season grasses which has been gained in Durban, South Africa, Wilhelmshaven, Germany and Auckland, New Zealand.

Sports Turf Construction Experience

My sports turf construction experience includes the construction of many sports fields for football, rugby hockey and cricket, golf course greens, bowling greens, turf wickets in Durban, South Africa over a period of more than 25 years mostly while working for the Durban Parks Department, which were all planted to warm season grasses in particular Cynodon dactylon varieties. I also constructed and renovated a number of football fields and rugby fields in New Zealand.

Amenity Turf Construction Experience

Most of my amenity turf construction experience comes from over 28 years constructing and maintaining parks and gardens for the Durban Parks Department, I also gained valuable experience as a private contractor constructing parks and establishing cool season grasses mostly for the North Shore City Council in Auckland New Zealand.

Sports Turf and Amenity Turf Maintenance Experience

Most of my sports turf and amenity turf maintenance experience comes from the maintenance of a large number of parks, sports fields, road verges etc that were under my direct care as a horticulturist then later as a horticultural manager during the 28 years that I was employed by the Durban Parks Department

Domestic lawn Establishment and Maintenance Experience

My domestic lawn establishment and maintenance experience has been gained on warm season grasses in Durban and on cool season grasses in Wilhelmshaven, Germany and Auckland, New Zealand. My first experience with domestic lawn care was gained as a young child helping my father do his annual spring treatment of our own domestic lawn up until today where I still do all my own lawn care including the cutting of my own lawn. I have also cared for lawn for commercial clients in South Africa, Germany and New Zealand over a period of over 40 years.

For a number of years I over seeded portions of my own domestic lawn in Durban in winter with cool season grasses to maintain a lush green lawn in areas that Cynodon dactylon had been planted.

Academic Achievements

Certificate in Turf Grass Management (Cum Laude)

Best Student Turf Grass Management Association 1984

Management of Warm season grasses

Lawn and Sports turf care Durban

Management of cool season grasses

Management of your lawn

Overseeding

Lawn Renovation

Preparation

Weed Control

Particular considerations for Auckland New Zealand

Making the case for a re-think on perennial rye (Lolium perenne) as a suitable lawn grass in the greater Auckland region

Care of Perennial Rye grass lawns