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Mechanical Weed Management
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Mechanical/ Physical Weed Management
By the end of this lesson, you should be able to -
define mechanical weed management
understand when and where mechanical management is appropriate
describe various techniques in mechanical weed management
understand the advantages and disadvantages to specific techniques in mechanical weed management.
Mechanical Weed Management
Mechanical weed management is the physical removal of weeds by:
mowing
mulching
tillage
thermal methods
hand-pulling
Photo courtesy of Rick Boydston, USDA-ARS.
Mechanical Weed Management
It should be part of an integrated weed management strategy.
Operator skill, experience, and knowledge are extremely important.
The site must be suitable for access of the machinery.
It is generally not practical for use on many hundreds of thousands of acres.
Mechanical Weed Management
Advantages
When using mechanical weed management techniques, herbicide use may be completely eliminated or significantly reduced.
Less herbicide pollution of ground and surface water.
Less human exposure to herbicide residues in food and drinking water.
Ideal for areas next to water.
It is effective on herbicide resistant weed biotypes.
It can be highly selective, especially in the case of hand-weeding.
Mechanical Weed Management
Disadvantages
Cultivation reduces soil organic matter.
May increase soil erosion and compaction.
Effectiveness is highly dependent on timing, soil moisture, and the weather.
Photo courtesy of Rick Boydston,
USDA-ARS.
Mechanical Weed Management
Disadvantages
May have less flexibility compared to other management techniques.
Within-row weeds are difficult to control.
It is often slow or generally inefficient – depending on the technique.
Photo courtesy of Rick Boydston, USDA-ARS.
Mechanical Weed Management
Disadvantages
Crops can be easily injured by mechanical techniques.
It is important to minimize the injury caused by mechanical techniques.
Loss in crop density is normal, and may vary from 1-25%.
Loss depends on the crop, crop stage, environment, equipment, and more.
You should take a stand count before and after mechanical techniques to evaluate the injury.
You can also increase the planting rate by approximately 10% to compensate for losses.
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Mechanical Weed Management
Many vegetables and sugarbeets are row crops that require intense weed management efforts.
Some of these row crops reach canopy closure and suppress weeds late in the season. Some crops never do.
Such as…
An option is to use a hoe or hand-pull weeds in these systems.
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Hoeing or Hand-pulling Weeds
It is the oldest forms of weed control.
Labor availability and cost may be problems
Used in many developing countries
Estimate for India – 1 billion days per year on hand weeding
Used in high value crops
Time consuming
up to 60 hours per acre in sugar beets
40-160 hours per acre in onion and leeks
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Flaming as Weed Management
Flaming before crop emergence is successful in slow germinating crops such as onion, leek, carrot, and corn.
Two general types of flamers available.
Covered flamer – flames to 3500 F
Infrared flamer – flames to 1700 F
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Flaming as Weed Management
Flamers use a liquefied gas or propane-butane mixtures as fuel.
Cell membranes and proteins are destroyed
Weeds must be small
Can get some selectivity due to rate and speed
Flamers can be backpack style for small areas, or tractor-drawn for larger areas.
A backpack unit can be constructed for approximately $100.
Flaming as Weed Management
Advantages
It produces immediate results.
It does not disturb the soil.
There is no chemical residue on the soil surface or in water.
Disadvantage
High consumption of fossil fuels.
Must be careful to avoid igniting dry vegetation.
It does not work well on monocot weeds – why?
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Burning as Weed Management
Open field burning is the process of burning cover vegetation for the purposes of
preparing the soil for crop production
weed control
clearing irrigation ditches
Photo courtesy of OSU
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Burning as Weed Management
Advantages
It produces immediate results.
It does not disturb the soil.
There is no chemical residue on the soil surface or in water.
Some ecosystems are generally well-adapted to fire.
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Burning as Weed Management
Disadvantages
Smoke is detrimental to public health and the environment.
Must be careful to avoid igniting dry vegetation.
Burning may select for some weeds, i.e., downy brome.
It is not long lasting, i.e., no residual control.
Many burn temperatures are not high enough to kill seeds.
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Soil Steaming as Weed Management
Mobile soil steaming is common in vineyards.
The equipment delivers steam from a boom or spray nozzle that is attached to a boiler.
Steam may reach 800 F.
It is possible for the steam to penetrate the soil and raise the soil temperature up to 6 inches deep.
Can get control for long periods, but not effective on all weeds.
Steamers cost $9,000 to $35,000.
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Soil Steaming as Weed Management
Advantages
Less risk compared to fire
Less dependent on environmental conditions
Disadvantage
High consumption of fossil fuels
Band steaming is available to reduce costs
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Steamers and Examples
Photos courtesy of OSU
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Tillage as Weed Management
Tillage controls weeds by uprooting or burying them, or both.
There are two main types of tillage.
Primary – breaking up or disturbing the soil
Moldboard plow and chisel plow
Secondary – the process of burying, pulling up, cutting off weeds
Double disk, roto-tillers, harrows, cultivators, etc.
Cultivation – after the crop has been sown.
Can be within and between rows.
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Optimum Conditions for Tillage
A dry and level soil surface
Allows for effective operation of equipment
Warm temperatures (75 F or greater)
Wind
Sunshine
Why?
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Tillage as Weed Management
Tillage is most effective on small weeds.
Tillage on wet soils can destroy the soil structure.
Shallow cultivation is better than deep.
Avoid bringing up new weed seeds
Expose tilled plants to surface so they will dry out
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Challenges Related to Tillage
Phenological and morphological similarities between the crop and weeds.
Indiscriminate and multiple flushes of weeds.
Perennial weeds may be spread by tillage.
Grower knowledge – a lot of art is involved.
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Many Different Styles of Tillage Exist
Early season, less aggressive tools
rotary hoe, flex tine harrows
Later season, more aggressive tools
sweeps, rolling cultivators, basket weeders, brush weeders
In-row tools
torsion bars, finger weeders
Precision guidance systems used with some tools
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Mowing as Weed Management
Mowing is aesthetically pleasing
Mowing must be done before seed set.
Ideally done before pollination and fertilization
Mowing must be repeated to deplete plant reserves.
May require up to six times per year
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Challenges Related to Mowing
Mowing is effective on upright weeds, but not prostrate ones.
Mowing may stimulate germination of underground buds.
Mowing may stimulate underground system to develop closer to surface.
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Challenges Related to Mowing
Some weeds become extremely woody later in the season, and are not effectively mowed.
Mowers and trimmers must be cleaned after using them for weed management.
Why?
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Mowing as Weed Management
Photos courtesy of OSU
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Mulching as Weed Management
Mulches control weeds by excluding light.
Any substance can be used but must exclude light
be relatively cheap
easy to work with
Common materials include black plastic and paper.
Plant materials - straw, sawdust, wood chips, bark, grass clippings, and more.
Perennial weeds not usually controlled very well.
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Challenges Related to Mulching
Mulching materials may be costly.
Not all weeds will be controlled.
Thin spots or tears will allow weeds to grow through.
Mulches may decay and need to be replaced.
If they don’t decay, they need to be removed at some point.
Mulches often limit other management techniques.
How??
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Mulching as Weed Management
before
after
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Integration of Techniques
Use a banded herbicide or mulch to control weeds within the row, and cultivate between the rows.
Photo courtesy of OSU
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Smother Crops
Crops that are maintained in dense stands to keep weed populations down.
Any crop that is well adapted for an area and is highly competitive can be used.
Alfalfa grown as a smother crop for 4 years reduced field bindweed by 95%.
Usually solid seeded or planted in narrow row spacing.
Examples - barley, corn, cereal rye, alfalfa, clover, sudangrass, buckwheat, and rapeseed.
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Use of Living Mulch
Photo courtesy of OSU
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Solarization
Capture heat from the sun and causing disruption
physical
chemical
biological
These changes kill weed seed and seedlings.
When properly done, the top 6 inches of soil will heat up to as high as 125 F.
Solarization provides the added benefit of controlling some
soil borne pathogens.
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Solarization
Solarization requires –
adequate soil moisture (field capacity is ideal)
a fine, smooth seedbed
time for it to work (approximately 4-6 weeks)
high sunlight and low wind
a solid tarp constructed of thin, clear plastic
The area to be solarized must be free of weeds and other debris at the start.
Debris can puncture the plastic, or lead to air pockets that slow the soil heating process.
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Solarization
Weed species differ in sensitivity.
Clovers are not controlled.
Most winter annuals are controlled after 4 weeks.
Most perennials require 6 weeks treatment.
The seeds of some perennials are controlled, but not the rhizomes.
After solarization, any seedbed preparations should be done
with minimal disturbance so that viable weed seeds are not
brought back up to the soil surface.
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Robots for Mechanical Weed Management?
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Robots for Mechanical Weed Mgmt.
A robot employs two vision systems:
gray-level vision system that is able to recognize the row
structure formed by the crops and to guide the robot along the rows
color-based vision system that is able to identify a single crop
among weed plants. This vision system controls a weeding-tool that removes the weed within the row of crops.
Source: Astrand and Baerveldt. 2002.
Autonomous Robots. 13:21-35.
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Mechanical Weed Management
This lesson provided information on –
a definition of mechanical weed management,
the utility and appropriateness of mechanical management,
various techniques in mechanical weed management, and
the advantages and disadvantages to specific techniques in mechanical weed management.
