Principles of Integrated Weed Management:
Non-Chemical Weed Control
| Author: |
OMAFRA Staff
|
| Creation Date: |
25 November
2002
|
| Last Reviewed: |
20 June 2008
|
Excerpt from 2008 Chapter 1, Publication 75, Guide to Weed Control, Order
this publication
 Table
of Contents
- Introduction
- Field scouting
- Crop rotation
- Cover crops
- Intercropping
- Nitrogen fertility
- Planting patterns
- Tillage system
- Preemergent or "Blind" Harrowing
- Weeder Harrow
- Rotary Hoe
- Inter-Row Cultivation
- Mowing
- Other topics in Integrated Weed Management
- Related links
Introduction
Non-chemical weed control can have many different approaches and success
can only be achieved when several approaches are integrated into the weed
management program.
- Identify and know your weed species - annual, biennal, perennial
- Have a planned approach (flexible strategy)
- Check fields regularly to adjust strategy
- Tillage practices - No-till, conservation tillage, moldboard
- Secondary tillage frequency, timing
- Stale seed bed
- Crop rotation - crop competition
- Crop and variety selection
- Time of planting
- Row spacing, crop population
- Use clean crop seed
- Cleaning equipment between fields (cultivators, combines)
- Prevent seed production from weed escapes
- Fencerows and boundary areas
- Avoid excess nutrients
- Composted manure
- Cover crops - keep the soil covered, crop competition
- Healthy, biologically active soils
- Weed seed predation
- Mulch - plastic or crop residues
- Harrow - after planting, pre-emergence of crop
- Rotary hoe - after planting, pre-emergence of crop
- Harrow - after crop emergence
- Rotary hoe - after crop emergence
- Row-cultivation
- Thermal - Flaming or steam/hot water
- Hoeing/pulling/walking the field
- Mowing
Field scouting
Field scouting is a key component of an IWM system. It involves the systematic
collection of weed and crop data from the field (weed distribution, growth
stage, population, crop stage, etc.). The information is used, in the
short term, to make immediate weed management decisions to reduce or avoid
economic crop loss. In the long term, field scouting is important in evaluating
the success or failure of weed management programs and for making sound
decisions in the future.
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Crop rotation
Crop rotation involves alternating different crops in a systematic sequence
on the same land. It is an important strategy for developing a sound long-term
weed control program. Weeds tend to thrive with crops of similar growth
requirements as their own, and cultural practices designed to contribute
to the crop may also benefit the growth and development of weeds. Monoculture,
that is growing the same crop in the same field year after year, results
in a build-up of weed species that are adapted to the growing conditions
of the crop. When diverse crops are used in a rotation, weed germination
and growth cycles are disrupted by variations in cultural practices associated
with each crop (tillage, planting dates, crop competition, etc.).
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Cover crops
The inclusion of cover crops — such as rye, red clover, buckwheat
and oilseed radish, or overwintering crops like winter wheat or forages
— in the cropping system can suppress weed growth. Fast growing crops
or crops exhibiting allelopathic properties can also suppress weeds. Highly
competitive crops may be grown as short duration "smother" crops
within the rotation. Additionally, cover crop residues on the soil surface
will suppress weeds by shading and cooling the soil. When choosing a cover
crop, always consider how the cover crop will affect the succeeding crop.
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Intercropping
Intercropping involves growing a smother crop between rows of the main
crop. Intercrops suppress weeds. However, approach the use of intercropping
as a strategy for weed control carefully. Intercrops can greatly reduce
the yields of the main crop if competition for water or nutrients occurs.
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Nitrogen fertility
Nitrogen fertilizer can affect the competition between crops and weeds,
and in the subsequent crops. For example, nitrate promotes seed germination
and seed production in some weed species. Nitrogen fertilization may increase
weed growth instead of increasing crop yield. Selective placing nitrogen
in a band can favour the crop over the weed. Using legume residues as
opposed to chemical nitrogen fertilizer to supplement nitrogen needs of
the crop can enhance weed suppression. Legume residues release nitrogen
slowly with less stimulation of unwanted weed growth.
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Planting patterns
Crop population, spatial arrangement and cultivar (variety) choices can
affect weed growth. For example, narrow row widths and a higher seeding
density reduces the biomass of later-emerging weeds by reducing the amount
of light available for weeds located below the crop canopy. Similarly,
fast growing cultivars can have a competitive edge over the weeds.
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Tillage system
Tillage systems alter the soil seedbank dynamics and depth of burial
of weed seeds. Studies show that almost 75% of the weed seedbank is concentrated
in the upper 5 cm of soil in no-till fields. In the moldboard plow system
however, the seedbank is more uniformly distributed over depth. Other
conservation tillage systems are in between these two systems.
Weed seedling emergence is often more uniform from shallowly buried weed
seeds and may result in better weed control. Weed seeds closer to the
soil surface are more likely to be eaten or damaged by insects, animals,
other predators and disease-causing organisms.
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Preemergent or "Blind" Harrowing
Blind harrowing consists of waiting until after the crop has been planted,
the seed is sprouted and the shoot is not yet emerged. At this crucial
time, the field is harrowed to kill the small weed seedlings that have
already sprouted. The crop will emerge shortly afterwards, having gained
a head start on the next flush of weeds. When properly carried out, this
method can be most effective in controlling annual weeds in large seeded
crops. In cereals, this blind harrowing will often provide adequate control
of annual broadleaf weeds. In row crops, it can be used to keep weeds
down until the crop plants are large enough to withstand other mechanical
control methods. Any type of light harrow can be used. Blind harrowing
must not be done on crops previously underseeded with grass or legume
seeds.
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Weeder Harrow
A weeder harrow has spring tines that are gentle enough not to harm the
cultivated crop, while uprooting or covering the smaller annual weeds.
Therefore, the relative size of the cultivated plants and the weeds is
important. Weeder harrowing will be most successful when used before the
crop emerges and can also be used post emergent in many crops. Some crop
population loss will result. Speed and pressure settings are important
to minimize plant loss. They can be used most effectively on field vegetables,
corn, soybeans and cereals.
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Rotary Hoe
The rotary hoe has "fingers" that lift and mix the soil, uprooting
small weeds. It is important to work at 10-20 km/hr for satisfactory results.
Best results are obtained during late morning or afternoon hours when
the hot sun can dry out the uprooted weeds. Also, crop plants tend to
be more pliable at this time and injury is reduced. Rotary hoes tend to
cause less crop damage than harrows. They are also effective in breaking
up a soil crust and mixing surface-applied herbicides into the soil, which
will improve the weed control. On light soils or under loose soil conditions,
care must be taken to keep the rotary hoe working at a shallow depth.
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Inter-Row Cultivation
Shallow inter-row cultivation or scuffling of row crops uproots small
weeds and cuts off larger weeds. Various types of equipment can be used
but, when shovels are used, allow for up to 50% overlap for thorough weed
control. Shields should be used to protect small crops.
Row cultivation can be used profitably when applying herbicides. The
herbicide may be more effective and the amount of herbicide used can be
reduced, particularly with band applications. To provide adequate weed
control in long-season crops, such as corn, scuffling will probably have
to be done more than once. The first cultivation is the most crucial since
weeds that escape this pass will usually grow to maturity. Here again
the relative size of the crop to the weeds is important and probably the
limiting factor in achieving 100% success. Use blind harrowing, weeder
harrows and/or rotary hoes first to complement the inter-row cultivation
to achieve success in non-chemical (organic) weed management.
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Mowing
Mowing or cutting weeds may control weeds in orchards, roadsides, lawns,
etc. Harvesting hay or cereal crops also helps to control weeds. Mowing
cereal stubble in August can reduce weed growth and weed seed production,
especially if the cereal had been underseeded to another crop such as
red clover to compete with the new weed growth. The best time to mow perennial
weeds is usually at the bud stage when root reserves are low and before
seed set. Note that if a herbicide application is planned for later in
the season, adequate time should be left for weed regrowth after mowing.
For more information, see individual crop sections.
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Related Links
For more information:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
E-mail: ag.info.omafra@ontario.ca
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