Getting a Grip on Lawn Weeds!

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Getting a Grip on Lawn Weeds!

• Matt Fagerness
• Kansas State University

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Weed Control Outline

• Turfgrass Species and Weeds in Kansas
• Herbicides and How They Work
• Control of Broadleaf Weeds
• Control of Grassy Weeds and Sedges

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Transition ZoneLots of Options for Turf and Weeds
Many turf species can grow in the transition zone
but cold winters and hot summers make it
difficult on turf and therefore can promote weed
invasion.
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Turfgrass Species for Kansas
Cool-Season Tall fescue Kentucky
bluegrass Perennial ryegrass Fine fescue Creeping
bentgrass
Warm-Season Bermudagrass Buffalograss Zoysiagrass
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Turfgrass and Weeds
The best defense against weeds is good quality
turf. Healthy, dense turf can shade out and
compete with weeds for water, nutrients, and
other resources.
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What are Weeds?

• In a nutshell, weeds are plants out of place.
• Weeds are defined by the consumer.
• Ex. Some people grow bermudagrass, some
  people want of get rid of it.

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Types of Weeds

• Knowing what weed youre dealing with and its
  life cycle are critical to effective weed
  control!
• Proper selection and application of herbicides
  should follow weed ID and site remediation.

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Types of Weeds

• Biology Breakdown
• Broadleaf (e.g. dandelion, clover)
• Grass (e.g. crabgrass, bermudagrass)
• Nutsedge
• Life Cycle Breakdown
• Annual (winter or summer)
• Perennial (hardest to control)

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Summer Annual Broadleaf Weeds

• Germinate in spring and flower/die in early fall
• Not as common in turf situations
• Examples
• Knotweed
• Field crop weeds (e.g. velvetleaf, lambsquarters)
• Spurges

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Winter Annual Broadleaf Weeds

• Germinate in early fall and flower/die in late
  spring
• More common in turf situations
• Examples
• Chickweed
• Henbit
• Speedwell
• Wild garlic

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Winter Annual Broadleaf Weeds
Henbit
Chickweed
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Perennial Broadleaf Weeds

• May reproduce from seeds or from storage
  structures like rhizomes or taproots
• Much more difficult to control
• Examples
• White clover
• Dandelion

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Perennial Broadleaf Weeds
Dandelion
White Clover
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Summer Annual Grassy Weeds

• Very commonly found and recognized in turf
• Germinate in spring and set seed/die in early
  fall
• Examples
• Crabgrass (smooth and large)
• Goosegrass
• Foxtail

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Crabgrass and Goosegrass
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Winter Annual Grassy Weeds

• Germinate in early fall and flower/die in late
  spring
• More common in turf situations
• Examples
• Annual bluegrass
• Hardgrass
• Little barley

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Annual Bluegrass
There are two common biotypes of annual
bluegrass, a true annual (shown at right) and a
weak perennial, which more frequently coexists
with bentgrass on putting greens.
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Perennial Grassy Weeds

• Reproduce from seeds and from storage organs
  (usually rhizomes)
• Hard to control selectively in turfgrass
• Examples
• Orchardgrass
• Bermudagrass

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Perennial Grassy Weeds
Bermudagrass
Orchardgrass
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Sedges

• Sedges are not grasses but can be confused for
  them. Sedges have triangular stems and appear
  shinier than do grasses, often outgrowing turf.
• Sedges can reproduce by seed but do so more
  prominently through underground nutlets.

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Yellow Nutsedge
Sedges are often indicative of moist, poorly
drained soils but can grow in many environments.
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Weed Control Outline

• Turfgrass Species and Weeds in Kansas
• Herbicides and How They Work
• Control of Broadleaf Weeds
• Control of Grassy Weeds and Sedges

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Herbicides are either

• Preemergence kill weeds before they get started
  OR
• Postemergence kill existing weeds
• Selective only kill certain types of plants OR
• Nonselective kill all plants
• Contact kill only tissue they directly contact
  OR
• Systemic move to all tissues to kill the whole
  plant

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Pre- vs. Postemergence Herbicides

• Preemergence herbicides, applied prior to when
  annual weeds germinate, form a barrier through
  which weeds can not pass. They do not prevent
  germination!!
• Postemergence herbicides are absorbed by roots or
  leaves of existing weeds and are then moved to
  the part of the plant where they do their dirty
  work.

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Selective vs. Nonselective Herbicides

• Selective herbicides target certain types of
  plants so we select herbicides which target our
  weeds but not our turf (e.g. 2,4-D, MCPP,
  dicamba)
• Nonselective herbicides are not picky about which
  plants they kill so we need to avoid them or use
  them with caution to prevent turf damage (e.g.
  most preemergence herbicides, Roundup, diquat)

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Contact vs. Systemic HerbicidesPostemergence

• Contact herbicides (e.g. diquat, bentazon) only
  kill plant tissues they directly encounter (less
  than ideal for perennial weeds)
• Systemic herbicides translocate (move) up from
  roots or down from leaves to target sensitive
  tissues in the plant (e.g. Roundup kills the
  root)

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Weed Control Outline

• Turfgrass Species and Weeds in Kansas
• Herbicides and How They Work
• Control of Broadleaf Weeds
• Control of Grassy Weeds and Sedges

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Broadleaf Weed Control Tips Hey, mow!

• Mowing can remove the terminal growing point,
  thereby limiting flowering and seed production
• catch benefit for mature weeds, ideally we want
  to kill them when younger

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Broadleaf Weed Control TipsChemical

• Attack perennial broadleaf weeds in fall when
  food reserves are low, again in the spring
• Attack annual broadleaf weeds before they start
  to flower (fall and early spring for winter
  annuals, late spring for summer annuals)
• Apply chemicals when weeds are actively growing
  (adequate moisture, fertility, etc.)

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Control of Broadleaf Weeds

• Use postemergence, selective, systemic herbicides
• 2,4-D dandelion and winter annuals in the fall
• Combination products dandelion and winter
  annuals in the early spring, summer annuals
• Trimec (2,4-D MCPP Dicamba)
• Weed-B-Gon (2,4-D MCPP)
• Confront (commercial) excellent on clover, safe
  on buffalograss
• Turflon products good on clover

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Common Pitfalls in Herbicide Use Broadleaf Weed
Control

• Insensitivity to drift potential (e.g. dicamba)
• Applying when annual weeds are mature
• Applying to perennial weeds in the wrong season
• Not using repeat applications on perennial weeds
• Applying too near to turfgrass establishment
• Applying when weeds arent actively growing
• Applying to a sensitive turfgrass species
  (buffalo)

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Weed Control Outline

• Turfgrass Species and Weeds in Kansas
• Herbicides and How They Work
• Control of Broadleaf Weeds
• Control of Grassy Weeds and Sedges

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Control of Grassy Weeds (Annual)

• Natural
• Higher mowing heights (shade impedes the weeds)
• Removing seedheads before they set seed
• Chemical
• Preemergence herbicides most effective
• Products Barricade, pendimethalin, Dimension,
  Treflan, Balan, Ronstar

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Tips for Annual Grass Control

• Apply before weeds germinate late summer (WA),
  early spring (SA)
• Before April 15 for crabgrass and goosegrass
• Before April 1 with Barricade (takes longer to
  activate)
• Use Dimension if application is late (only
  preemergence product with any postemergence
  activity)
• Split applications 8 weeks apart may be necessary
  to cover germination window
• Possibility of late fall applications??

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When PRE Herbicide Strategies Fail

• Timing
• 1 cause of failure for preemergence applications
• Crabgrass germinates when soil temp.s reach 55
  F, goosegrass closer to 60 F.
• Summer breakdown
• Germination window for crabgrass and especially
  goosegrass extends past life of herbicide in soil

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Solutions for Early Germinating Summer Annual
Weeds

• Apply at first sight of conditions conducive to
  crabgrass/goosegrass germination
• Open to interpretation, poor consistency, hard to
  predict, etc.
• Apply PRE herbicides in fall to catch early
  germinators
• Good for PRE herbicides with good residual
  activity
• Options for commercial and homeowner turf

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Fall PRE Herbicide Efficacy on Crabgrass (1995)
Data collected at Rocky Ford Turfgrass Research
Center All rates in lb. a.i./acre
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Solutions for Weeds Which Outlast Preventer
Herbicides

• Split applications between early and late spring
• Essential for herbicides with shorter shelf
  life in soil
• May cause fall seeding troubles with more
  persistent herbicides
• Split applications between fall and late spring
• Fall applied herbicide catches early season
  germination (1/2 to 2/3 total product)
• Spring applied herbicide catches summer
  germinators just as fall applied herbicide
  fizzles out.

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Solutions for Escaped Summer Annual Weeds

• Postemergence control of crabgrass/goosegrass
• Commercial products available for use in our
  major turfgrass species (Drive, Acclaim Extra)
• Fewer products (e.g. Trimec Plus w. MSMA)
  available for selective use in cool-season home
  lawns

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Postemergence Crabgrass Control in Bermudagrass
All herbicides applied at label recommended
rates 7-1-99.
Data collected 8-19-99, courtesy of F.H.
Yelverton, NC State University
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Problematic Perennial Grassy Weeds

• Bermudagrass (love it or hate it)
• Rhizomes and stolons
• Orchardgrass
• Bunch type but tillers aggressively, produces
  seed, and has a strong, perennial root system

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Control of Grassy Weeds (Perennial)

• Natural
• Mechanical
• Use of certified high quality turfgrass seed
• Chemical
• Fusilade (fluazifop) may suppress bermudagrass
  but requires more than one application
• Spot-spraying or renovation with a nonselective
  herbicide

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Control of Perennial Grassy WeedsOption A
Mechanical Removal

• Laborious and often disruptive
• gaps where orchardgrass or bermuda patches used
  to be
• Not always reliable
• spreading nature of bermuda is such that physical
  removal usually does not eradicate all plant
  material

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Control of Perennial Grassy WeedsOption B -
Nonselective

• Always an option but not always practical
• Available products
• Roundup (glyphosate)
• Finale (glufosinate)
• Reward (diquat)
• Vantage (sethoxydim)

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Nonselective Bermuda Control
Data collected at Rocky Ford Turfgrass Research
Center, Fall 1996
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Control of Perennial Grassy WeedsOption C -
Selective

• Fewer products but the most desirable option
• Bermudagrass only (no known options for
  orchardgrass)
• Available products
• Acclaim Extra (fenoxaprop) w. Turflon Ester
  (triclopyr)
• Fusilade II (fluazifop)

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Selective Bermuda Control in Zoysia
Note Acclaim did not discolor tall fescue while
Fusilade only discolored tall fescue 18 in a
similar study.
Data collected at Rocky Ford Turfgrass Research
Center, Fall 1996
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Control of Sedges

• Natural
• Aerify or remediate poorly drained soil
• Mowing may reduce nutlet production
• Chemical
• MSMA, Basagran and Manage are all used
• Manage may be the best for a variety of
  turfgrasses
• Repeat applications may be necessary to get
  complete control

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