Introduction to Weed
Management Principles
Topic #2044
Aaron Gearhart
What is a Weed?
• Any plant can be a weed under the
right circumstances
• Corn example
• Soybean example
• It all depends on what type of
production you are trying to
accomplish
Why care?
•
•
•
•
Food costs
Aquatic nuisance
Allergies
Hosts for diseases
and insects
Dandelion
http://www.noble.org/imagegallery/Forbhtml/Dandelion.html
Why care?
• Increased soil
erosion
• Decreased amount
of food we can
produce
• Decreased grazing
area
http://www.noble.org/imagegallery/grasshtml/Barnyardgrass.html
Barnyard Grass
Why are they so difficult to
control?!
• Can sprout in many
environments
• Long – lived seed
• Variable seed
dormancy
• Rapid growth
• High seed
production
Burdock
http://www.vet.purdue.edu/depts/addl/toxic/plant02.htm
So difficult.
• Effective dispersal
habits
• Allelopathy
• Deep root system
• Waxy or pubescent
leaves
Milkweed
http://www.vet.purdue.edu/depts/addl/toxic/plant26.htm
Weed germination
• Stratification
• Vegetative
reproduction
• Scarification
Johnsongrass Seedling
http://www.weedscience.org
Classification
• Grasses
• Broadleafs
• Sedges
• Annual
• Biennial
• Perennial
Grass Weeds
• Hollow rounded
stems
• Parallel veins
• Longer than they
are wide
Witchgrass
• Johnsongrass,
foxtails, crabgrass
http://www.noble.org/imagegallery/grasshtml/CommonWitchgrass.html
Broadleaf weeds
• Highly variable
• Have showy
flowers
• Have different
growth habits
Ladysthumb
• Velvetleaf,
ladysthumb,
dandelion.
http://www.weedscience.org
Sedges
Yellow Nut Sedge
• “grass like” but not
true grasses.
• Solid traingular –
shaped stems
http://www.noble.org/imagegallery/grasshtml/YellowNutgrass.html
Annual Weeds
• Complete their life cycle in one year
• Can be grasses, broadleaves or
sedges.
• Can be summer or winter annuals
• Not many winter annuals in Michigan
Biennial Weeds
White campion
• 2 year life cycle
• First year
vegetative growth
• Second year flower
and seed
production
• Onions are a good
example.
http://www.fragrantflowers.co.uk/picture/whitecampion.htm
Perennial Weeds
• Live more than two years
• Reproduce by vegetative parts
– Tubers, bulbs, rhizomes, stolons
• During winter most survive in a
dormant state.
Seed Characteristics
Redroot Pigweed
• Redroot pigweed
can produce
100,000 seeds in
one plant.
• Dormancy ensures
weed survival
• 4%broadleaf and
9%grass seeds
germinate in a
given year
http://www.noble.org/imagegallery/Forbhtml/RedrootPigweed.html
Methods of Control
•
•
•
•
•
Prevention
Chemical
Biological
Mechanical
Controlled
burning
• Grazing
• Revegetation
• Crop
competition
• Crop rotation
Prevention
• Weed seed may be
distributed in a number
of ways
• Crop seed, wind, water,
animals, machinery
and other ways
• Neglected fence rows
and ditches
• Proactive thinking
Chemical
Bull Thistle
• Use of chemicals
to control or retard
growth of weeds
• Allowed us to
become an
agricultural
powerhouse
• Very useful if
application is well
thought out
http://www.noble.org/imagegallery/Forbhtml/BullThistle.html
Time of Application
• Preplant: made before crop is
planted and is incorporated into the
soil
• Preemergence: Made directly to soil
and requries rainfall in order to move
into the soil
• Postemergence: Applied after weed
or crop emergence
Area of application
• Broadcast
• Band
• Directed
• Spot treatments
Types of Herbicide
• Contact herbicide: sprayed on
foliage and only affects area it comes
into contact with
• Systemic herbicide: sprayed on soil
or foliage then translocated through
plant
• Selective
• Non-selective
Factors Affecting Herbicide
Effectiveness
•
•
•
•
•
Annual or perennial
Tolerance
Type of soil
Temperature
Pubescence or wax
on leaves
• Shape/orientation
of leaf
Biological Control
• Using beneficial
creatures such as
insects or fungi
that damage the
weeds
• Not very common
Mechanical
• Burial
• Cultivation
• Tillage
• Mowing
Controlled Burning
• Not very common
• Sometimes used
when corn 1-2” tall
and growing point
is still under the
soil
Grazing
• Use of animals
such as sheep or
goats that will eat
weeds and weed
seeds.
Revegetation
Hairy Vetch
• Reseeding a
distubed site to
block or choke out
weeds
• Cover crops are a
good example
http://www.noble.org
Crop competition
• Planning your planting so that crops
have the competitive advantage over
weeds.
• Factors such as planting date, row
spacing, seeding rate, planting depth,
soil moisture, fertility, and soil pH
have an influence on competitive
advantage of the crop.
Crop rotation
• Rotating your crops from year to year
and season to season to take away
competitive advantage from weeds of
the previous years crop.
Are weeds all bad?
Lambsquarters
• Quickly fill in
unsightly spots
• Shelter for
beneficial insects
• Beneficial
properties for
humans
• Provide food for
wildlife
http://www.noble.org/imagegallery/Forbhtml/Lambsquarters.html
Integrated Weed
Management
• An integrated
approach means
assembling a weed
management plan
that incorporates a
number of tools
consistent with
farm goals.
Field Bindweed
http://www.noble.org/imagegallery/forbhtml/forbs151-200/F1715.jpg