1. Time of weed/crop emergence

2. Growth Form

3. Weed density

4. Physiological Basis of Competition - above ground

5. Physiological Basis of Competition - below ground

Factors Affecting Weed/Crop Interference

1. Time of weed/crop emergence

Factors Affecting Weed/Crop Interference

2. Growth Form

a)root form - tap vs fibrous, bunch vs spreading

b) height - prostrate vs direct growing

c) leaf area

d) free branching vs single stalk

-Distinct advantage of rapid growth with a tall dense canopy

-Lower advantage of slow growth rate with a thin canopy

-Highly dependent on crop

Factors Affecting Weed/Crop Interference

3. Weed Density

-As weed density increases, severity of crop damage increases

-SEE GRAPHS

Factors Affecting Weed/Crop Interference

4. Physiological Basis of Competition - above ground

a) light - often most cirtical

-leaf angle

-rapid expansion of a tall canopy

-large leaves

-light compensation point

-climbing height

-high allocation of dry matter to stem

b) C4 photosynthesis - under conditions of limiting CO2

Factors Affecting Weed/Crop Interference

5. Physiological Basis of Competition - below ground

a) Root Morphology

-early are rapid root penetration

-hight root density

-distribution - fibrous roots spread over wide area, thus more effective

b)nutrients - weeds are better at obtaining nutrients

-nitrogen - main

-phosphorous and potassium - more a factor in perennial

-nutrient management - low in legumes, P promotes poa annua in bent

c)water

-more of an issue under irrigated conditions

-becomes more of a limited factor during fruit/seed development

1) row spacing - narrow spacing allos for quicker canopy coverage

2) fertilizer placement - in the row near the crop

3) drip irragation - in the row near the crop

4) breeding - some varieties are better adapted to weedier conditions

1) crop quality - hard to measure quantitatively, critical in vegetables

2) harvest losses - hard to seperate from direct competition

3) interference with other pest contiol methods

4) hand harvesting - fireweed in vegetables

5) staining of cotton

One plant chemically interfering with the growth of another plant

Koch postulates

One plant physically interferes with the growth and development of another plant

recieve partial or all growth requirement form the host plant

fully phothsynthetic (mistletoe) or non-photosynthetic

attaches by means of specilized structures

- sticky seeds (mistletoe)

-exploding seed pods (dwarf mistletoe)

-host-excreted stimulant

1. preventitive

2. cultural

3. mechanical

4. biological

5.chemical

1. monitor seed and vegetative populations

2. identify problem weed speices

3. predict weed population shifts

4. decide weather control is needed

5. chose control technology

6. consider grower resources ($$$)

7. evaluate long-term impacts and options

system by which all available toos are used to reduce seed seedbank, prevent weed emergence with other plants, and minimized competition

or

the use of all methods in an intraged apporach to effectively manage weeds in a short and long term approach

-prevented entry of weeds of forgien origin

-established and enforced quarentines

-controlled and eradicated weeds with potential for great loss

Established Seed Labels

-% of pure seed

-% of other crop seeds

-% of weed seeds

-list of noxious weed seeds and their rate

1. do not let weeds reproduce (kill prior to seed set)

2. do not buy weed seeds in uninfested areas

3. do not plant infected crops of transplants

4. do not feed weed screenings to livestock

5. clean machinery when moved from one site to another

6. kill weeds in surrounding areas

Cultural Weed Management

Crop Rotation

-prevents severe infestations of one or a few weeds DUE TO:

-differing planting and harvesting dates

-different competitve ability

-differing fertility, water, etc

-monocultures have typically greater weed infestations

Cultural Weed Management

Planting Date

-rapid and even emergence of the crop is critical to crop vigor and competitive ability

-planting a crop to early will often result in poor germinations and low plant population, low soil temperature

Cultural Weed Management

Spatial Arrangement

-reduced row spacing favors crop competitiveness

-limitation in row crops is equipment for plating, cultivation and harvest

-home gardens, plant as close together as possible, however tight spacing will increase disease and incest population

Cultural Weed Management

Seeding Rate

Cultural Weed Management

Cultivar differences

-some cultivars do better than others

a) corn - late maturing less competitive than early maturing

b) wheat - normal height more competitive that semi-dwarf, however dwarfs yield more, so chemical control is used

c) peanut - Dixie-Runner has spreading growth habit and a better yield when grown with weeds than newer varieties like Florunner

Cultural Weed Management

Soil Fertility

-species able to utilize soil nutrients will have competitive advantage

a) wild oat can take advantage of nitrogen earlier than wheat

b) N and P amendments can increase grassy weed infestations

-low N in turf, increase in black medic and legumes

-high N in turn, increase of poa and chickweed

c) fertilizer placement - decrease weed competition by banding fertilizer in the row

Cultural Weed Management

Soil pH

-adjusted to meet the needs of the crop

-6-6.5 is best for uptake of nutrients

Weeds As indicators of:

a) Low pH

b) compaction

c) poor drainage

d) low nitrogen

e) high pH

a) red sorrel (sourweed)

b) groosegrass and plantains

c) sedges and pennywort

d) legumes

e) plantains

-an open area that invites weeds (turf and ornamential)

-can be an issue with perennial forages and natural areas

-can also be considered an issue with not achieving proper stand in an agronomic or horticultural crop

-Environmental Stress - flooding, hail, drought, lightning, hurricanes

-animals - wild hogs

-Disease, insects, nematodes

1) improper mowing

2) improper fertility

3) improper irrigation

4) lack of core cultivation

5) lack of thatch managment

6) lack of traffic control

Cultural Weed Management Strategies

Summer annuals

-avoid establishment at time of grass germination

-avoid verticutting or core cultivation at the time of germination

-lower mowing height and bucket during seed setting

-relieve compation for goosegrass

-pre-emerge before germination temperatures are reached

Cultural weed management strategies

winter annual grasses

-most competitive at close mowing, high water, high nitrogen

-correct drainage, raise mowing height

-avoid cultivation at germination temps

-collect clippings at time of high seed production

Cultural weed management strategies

Perennial weeds in turf

-maintain dense turf through proper fertility, mowing, insect, disease control

-spot treat or remove isolated patches

-post-emerge in fall

Biolgical Control

Definition

Biological Control

Objective

1) host specific or other non important host species that will support it

2) effective in control, reduced to non-harmful levels

3) faborable host-plant synchroniztion with the natural enemies life cycle

4)be prolific and thrive in widespread areas

5) good colonizers

1) Perennial crops, low input cropping systems

2) rapid control not necessary

3) complete control not needed

4) monoculture of one target weed

5) natural ecosystems are ideal situations

-most row crops and turf - damage before effective control, many different weeds

-biocontrol requires leaving some of the weed, not ok in turf settings

-biocontrol needs to feed off weed, therefore damage is already done to cropping systems before the biocontrol system can work

1) weeding by hand

2) Tillage

3) mowing

4) large equipment

5) mulches

6) flooding

7) fire

Mechanical Weed Management

Weeding by hand

- hand pulling

-hoeing

-garden tools

-primary method in under-developed areas

-expensive

-highly selective and often only method (vegetable operatons, $500-$900/acre)

Mechanical Weed Management

Tilliage

reasons for using tillage (advantages)

-breaks weeds apart

-causes dessication

-exausts feed reserves

-reduces seed and/or vegetative propagule bank

Mechanical Weed Management

Tillage

Disadvantages

-exposes soil to wind and water erosion

-burries weed seed, ensures survival through dormancy

-deep tillage can bring weed seeds to surface

-damage crop roots

-causes soil compaction

-several tillage operations must be done to be effectvie - $$$

Mechanical Weed Management

Tillage

Typical tillage scenario

conventional planting

-break ground with moldboard plow

-break clods with disk harrow

-spring tooth harrow 2x to smooth

-Plant

-cultivation - 2-4 times, depending on crop

Mechanical Weed Management

Tillage

typical tillage scenario

concervation planting

-plant directly into previous crop residue

or

-deep chisel plow follwed by direct planting

or

-tillage in small strip, then plant directly into strip

Mechanical Weed Management

Tillage

Cultivation

-In-row tillage

-plant crops in parallel rows and use tillage to keep middles clean