Principles of Weed Control

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Principles of Weed Control

• Pastures
• Right of Ways
• Lawns

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What is a Weed?

• Dallisgrass in Bermudagrass
• Bermudagrass in Alfalfa
• Alfalfa in flowerbeds
• Basically, it is any plant that you do not want.

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Know Your Weeds

• 300 different plant species
• in Northeast Texas

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Only a Handful Economically Significant

• Woolly Croton Milkweed
• Pigweed Berryvine
• Ragweed Thistles
• Bitterweed Buttercup
• Horsenettle Grassburs
• Dogfennel Bahiagrass
• Dallisgrass Crabgrass

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Weed Identification

• Plant type
• Root growth patterns
• bulb, tap, fiber, creeping
• Life Cycle annual, biennial, perennial

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Broadleaf plant structure
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Grass Identification

• Leaf shape is lancelike
• Reproductive organ
• Seedheads
• Stolons/Rhizomes
• Tillers
• Growth habits
• Upright
• Prostrate

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Reproductive Organs

• Simple Produces only seeds with and without
  tillers (crabgrass)
• Bulbous forms bulb and seed (false garlic)
• Creeping produces seed, and growing reproductive
  organs such as stolons and rhizomes (bahiagrass)
• Combination of the above (bulrush)

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Weed Invasion Requirements

• Stratification
• cool period after seed fall
• plant specific
• Moisture
• seed swell
• Sunlight
• Open sod

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Weed Persistence

• Nutrient Reserve is key issue.
• The older the plant is and the more nutrient
  storage (reproductive) organs the plant
  possesses, the harder it is to control.

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Keys to weed persistence

• Seed crop size
• Seed hardness
• Nutrient Reserve
• Size the bank account
• Location underground is tough
• Defenses (resistance to defoliation)

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Battle Plan

• Annuals
• annual seed production required
• kill flower, prevent seed formation
• Early (pre-emergent) control is best
• Perennials
• Kill root, kills plant
• Nutrient Reserve Depletion required
• Control timing critical and weed specific

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Weed Control Methods

• Mechanical
• Biological
• Crop Rotation
• Fire
• Crop Competition
• Prevention
• Chemical

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Mechanical Weed Control

• Tillage
• Plow
• Cultivation
• Burial
• Mulch
• Crop cover
• Mowing
• Mowing
• Hay Harvest

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Tillage

• Plowing
• primary form of establishment weed control
• Cultivation
• Works in rows, ineffective in broadcasts
• Problems
• Destroys root system of weed
• Deep cultivation may hurt crop
• Deep cultivation may bring up weed seeds
• Expense (?)

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Burial

• Placing soil or mulch or other material over the
  reproductive organ
• Effective with seed
• Ineffective with plant parts (bulbs , rhizomes,
  etc.)
• May destroy perennial crop
• Living mulch possible
• pastures and ROWs

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Mowing

• Effective on tall growing annual weeds (redroot
  pigweed)
• Ineffective on short growing perennial weeds
  (dallisgrass)
• or plants shorter than crop
• Little benefit for current years grass program
• Timing is critical

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Biological

• Lots of opinions
• Method
• Defoliation
• Desiccation
• Disease
• Insect
• Limited known control
• Disease
• Limited known control
• Mammals
• Possible

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Biological

• Effectiveness
• Effective
• plants of similar palatability and different
  growing patterns
• Johnsongrass in bermudagrass
• different livestock species
• cattle/goats, horses/sheep
• Ineffective
• Plants of similar palatability and growth pattern
• Toxic plants

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Crop Rotation

• Replacement of one crop with another
• Allows use of cleanup herbicide program
• Works best with annual crops
• Usually not economical in perennial crops but may
  be required severe weed problems

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Fire

• Earliest recorded form of grass management
• Multiple benefits (residue removal, control of
  spring weeds, increased infiltration)
• Effective on young annual weeds
• Ineffective on many perennial weeds
• Fuel load is critical
• 1500 lb. dm/ac.

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Fire

• Timing is critical
• May damage crop plant
• VERY RISKY, HIGH LIABILITY
• Not recommended to most producers, land owners or
  anyone
• Check with Law Enforcement and Fire Stations
  first.

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Crop Competition

• Long term solution
• most economical
• Requires compatible and useable crops
• Growth patterns
• Defoliate properly
• Proper soil fertility levels required
• K and other deficits

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Effect of N Rate, herbicide and covercrop on weed
production
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Bermudagrass Defoliation

• Pastures
• Regular defoliation
• Intense defoliation in spring and early summer
• stubble
• Reduce intensity in late summer and allow
  nutrients to accumulate in roots
• stubble 4

• Lawns
• Cut short (
• Mow to match growth rate
• 1 per week in early spring or late fall
• 2-3 times weekly May through August (?)

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Liebergs Law of Limits
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Nutrient removed (lbs./ac.)by grazing and hay
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Influence of Nitrogen and Potassium on Coastal
Bermudagrass Survival
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Prevention

• Vigilance required
• Minimize soil disturbance
• Keep adjacent areas, etc. mowed
• Bring new items into weedy areas
• New Seed
• Out of region hay
• Wildlife feeders
• Keep grass crop vigorous and competitive

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Chemical weed control

• Pasture
• Limited number of herbicides (10
  w/brush)
• Price based on Income potential
• Right of Way
• Large number of herbicides (20)
• Price compared to labor costs
• Lawns
• Extremely numerous herbicides (50)
• Chemical cost is the price part of art?

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Labeled Pasture HerbicidesBroadleafs

• 2,4-D annual broadleaf
• Dicamba Weedmaster
• Picloram Grazon PD
• Sulfanyl Urea Ally, Amber
• specific weed tolerance and susceptibility
• Rave Dicamba Amber

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Labeled HerbicidesGrasses

• Weedmaster Sprigging bermudagrass
• Velpar smutgrass
• Ally bahiagrass
• Roundup new uses
• Gramoxone afternoon applications

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Basic Principles of Chemical Weed Control

• Know your weeds
• Choose the right herbicide
• Match equipment with needs
• Calibrate your sprayer
• Spray at the proper time
• Read and FOLLOW label instructions

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Summary

• Identify the weed and the crop
• Timing is everything
• Integrated Pest Management
• Starve the weed, feed the crop
• Mulch, Mow, Graze, etc. in the best manner
• Seek multiple benefits
• Chemical Weed Control
• Spray annual weeds when young and actively
  growing
• Spray perennial weeds at full leaf or fruit set