Weeds L5 Flashcards
4 approaches to weed management
Prevention, eradication, control, management
Weed prevention
preventing the introduction, establishment, and spread of weed species in areas not currently infested
Weed eradication
the complete elimination of all live weeds, weed parts, and weed seed from an area
Weed control
Reducing weeds to minimize weed competition and provide the greatest economic return from the crop
Weed management
the combination of the techniques of prevention, eradication, and control to manage weeds in a crop, cropping system, or environment
Forms of integrated weed management
Mechanical (physical) control
Cultural control
Biological control
Chemical control
Every weed management option is a ____________ on the weed population
selection pressure
What is the most practical approach to weed management?
weed prevention
Weed prevention practices
avoid using crop seed infested with weed seed
clean farm machinery thoroughly before moving to a different field
monitor field for new weed problems and remove them before they get out of hand
compost manure prior to field application
Common methods of mechanical weed control
hand-pulling
hoeing
mowing
tillage
Hand-pulling
physical removal of weeds by hand
effective against annuals, biennials, and upper portions of perennials
Hoeing
Cheap method of removing weeds
effective against annuals and biennials, but less effective on perennials because it only destroys top growth
Mowing
Machine operated practice that should be done before flowers open to prevent seed production
more effective on tall weeds than short ones
What does mowing success on weed management depend on
repeated mowing to deplete weed’s food reserve
mowing should be done between full leaf development and flowering because food reserves are the lowest
tillage
non-chemical weed control that removes weeds from soil and buries them
works best under dry, hot conditions
How does tillage influence weed composition?
increases # of perennial and annual species that have seeds with long life spans
type and frequency of tillage influences composition and density of weed species
Pre-seeding tillage
prepares seed bed so planting occurs at uniform depth and controls weeds prior to seeding
negative effects of pre-seeding tillage
lose moisture and cause erosion, inhibiting successful crop establishment
post-harvest tillage
shallow tillage that avoids burying weed seed that is effective in controlling winter annuals, biennials, and some perennials
Smmerfallow tillage
Shallow tillage to avoid bringing weed seed to surface that is partially effective in controlling perennials and dormant seeds of annuals
post seeding tillage
done by harrowing, rotary hoeing, or using a rod-weeder to kill weeds that emerge before the crop (important to ensure that crop has not sprouted in the tillage zone)
At what conditions will you receive the best result when using post-seeding tillage
a warm sunny day when the soil is dry
post-emergence tillage
done on weeds that emerge shortly after crop
tillage cannot be deep and a certain amount of crop damage is likely to occur
Row-crop tillage
Crops are planted in wide rows to allow for inter-row tillage (can cause more weed germination so multiple passes are necessary)
Flooding
roots and shoots of weeds are covered by water for long periods of time to deprive weed of air
Mulching (smothering)
use of non-living material/mulch to exclude light from weeds
allelopathic mulches
crop species that release allelopathic chemicals that can be used to retard weed growth
Example of allelopathic mulch
crop residues of fall rye incorporated into soil to inhibit weed species like wild oat
Sweet clover as green manure
soil solarization
Transparent and opaque polyethylene sheets are placed on moist soil to produce high soil temps that kills weeds (seedling/seed) and pathogens
Flaming (burning)
use of flames generating a high enough temp over a sustained period of time to kill weeds and seed within top soil layer
Cultural weed control
crop management practices that optimize the growth of crop plants and enable the crop to compete more effectively with weeds
Crop rotation effect on weed control
can have greater weed control effect than tillage (especially when using weed suppressing cover crops)
Seeding date effect on weed control
Seeding time is the main factor that determines weed composition as it is essential that the crops develop a good uniform stand in order to compete
Benefits of delayed seeding
offers tillage options before seeding and after harvest to control early germinating weeds
Types of weeds that can be controlled by late seeding
controls wild oat, wild buckwheat, and certain mustard species
how does varying seeding dates limit weeds ability to adapt
doesn’t allow them to germinate earlier or later to avoid control methods
seeding rate effect on weeds
Increasing seed rates 20-50% above normal can increase competitiveness of some species (can only be increased to a certain limit)
What does increased seed rate do to the crop
Earlier crop maturity (few days)
Reduced tillering and shorter
Higher yield (to a certain limit)
increase competition, disease, and lodging losses
When should increased seed rates be used
when either post-seeding or post-emergence tillage is planned to compensate for any crop damage
Seeding depth effect on weeds
Seeds are placed at optimum depth to allow quick and even emergence to give crops better competitive ability
What does optimum seeding depth depend on?
crop species
seed size
soil type and moisture conditions
General rule for seeding depth
planted around 2-3 times as deep as the height of the seed
Row spacing effect on weeds
narrow spacing means less open space for weeds to grow and offers better competition advantages for less competitive crops
Plant nutrition effect on weeds
insuring soil nutrients is balanced to keep crop healthy and give it a better advantage
