Master Gardener Training Weed Identification and
Management
Jeffrey Derr
Professor of Weed Science
Virginia Tech
Additional information
- Weed identification Books
• Weeds of the Northeast – Cornell Press
• Weeds of Southern Turfgrass, Georgia
Cooperative Extension Service
• Weeds of the South - University of Georgia Press
• Color Atlas of Turfgrass Weeds – John Wiley &
Sons
Additional information
• Pest Management Guides
Home Grounds and Animals
http://pubs.ext.vt.edu/456/456-018/456018.html
• Herbicide labels
Additional Information – Weed ID Websites
Virginia Tech Weed ID websites
www.ppws.vt.edu/ipm/weeds_container_nurseries
.html
www.turfweeds.net
www.ppws.vt.edu/weedindex.htm
What is a weed?
Prickly pear cactus
Purple loosestrife
What is a weed?
Plant out of place, growing were it is not
needed or wanted
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Purple loosestrife (Lythrum)
Prickly pear cactus
Bamboo
English ivy
Why control weeds?
Reasons to Manage Weeds
Competition
- leading to reduced crop growth and yield
(quantity, quality)
• for water (drought years)
• nutrients (especially nitrogen) –cannot
correct with extra N
• light (viny weeds)
• pollination (dandelion blooms) – reduced
crop pollination)
Reasons to Manage Weeds
• Harbor insect and disease pests (dandelion and
tomato ringspot virus, buckhorn plantain/aphids)
• Attract bees (problem for those allergic to bee
stings)
• Interfere with harvest (rash - poison ivy, spines brambles)
• Allelopathy (natural herbicides) - juglone – black
walnut
• Provide cover for rodents
Reasons to manage weeds
• Adversely affect human health – rashes
(poison ivy), poisonous if eaten (black
nightshade), allergies (common ragweed),
thorns (greenbrier)
• Reduce aesthetic value of lawns and
gardens
• Block visibility along highways
• Block water flow in ditches
Weed names
• Common names – differ across state, country
(stickweed, wiregrass, silver crabgrass, etc.)
Weed scientists used an approved list of common
names for the US (horseweed, bermudagrass,
goosegrass)
• Scientific name – used throughout the world
Eleusine indica (goosegrass)
Weed life cycle
Annuals
Summer - grass, broadleaf, sedge, other
monocots
Winter – grass, broadleaf
Biennials – broadleaf
Perennials – grass, sedge, other monocots,
broadleaves
Summer annual grasses
Large
crabgrass
Goosegrass
Giant foxtail
Microstegium (Japanese stiltgrass)
Winter annual grasses
Italian (Annual) ryegrass
Annual bluegrass
Annual broadleaves
Summer
common lambsquarters, smooth
pigweed, common ragweed, ivyleaf
morningglory
Winter
vetch, horseweed, fleabane,
common chickweed, henbit
Summer annual broadleaves
Common ragweed
tall morningglory
Common lambsquarters
Smooth pigweed
Winter annual broadleaves
Vetch
Henbit
Common chickweed
Horseweed
Biennials
Musk thistle
Wild carrot
Perennial Monocots
Perennial grasses
• clump - tall fescue, orchardgrass
• creeping - quackgrass, bermudagrass,
johnsongrass
Perennial sedges – yellow nutsedge
Other perennial monocots – wild garlic
Perennial grasses
Johnsongrass
Bermudagrass
Quackgrass
Yellow and Purple Nutsedge
Perennial sedges (rhizomes, tubers)
False Green Kyllinga – perennial sedge
Other monocots
Wild garlic (perennial)
Perennial broadleaves
• Simple – dandelion, buckhorn plantain
• Creeping - bindweed, brambles, poison ivy,
horsenettle, hemp dogbane
Simple perennial broadleaves
Dandelion
Buckhorn plantain
Creeping perennial broadleaves
Poison ivy
Horsenettle
Hedge bindweed
Perennial broadleaf weeds
Hemp dogbane
Black locust
Turf Weed Control
• Biological – none available
• Cultural
• Chemical
Integrated Pest Management
Determine management level – high, medium, low
Scouting – identify weed problems
late spring for winter annuals
late summer for summer annuals, perennials
Determine weed infestation level/need for renovation
Evaluate control options – nonchemical vs chemical
Chemical treatments – broadcast, spot-treatment
Cultural Control of Weeds in Turf
Use the best adapted turf species for the site
Proper mowing heights : 3-4 inches for tall fescue
Maintain appropriate pH, nutrient levels, irrigation
Correct compaction, shade, and drainage problems
Control insects and diseases
Reduce stress – drought, excess salts, etc.
Biorational Products for Turf
Corn gluten
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By-product of corn milling
60% protein
Preemergence herbicide
Annual weed control, esp crabgrass
No postemergence effects
~ 10% nitrogen
Herbicidal components
Various products Safe Lawn, WOW!, A-Maize-N,
Organic Weed and Feed, etc
Chemical Control in Turf
• Preemergence herbicides – primarily
for annual weeds
• Postemergence herbicides – primarily
used for perennial weeds
Crabgrass control in turf
Preemergence
Pre + Pre
Postemergence
Pre + Post
Preemergence Crabgrass Herbicides
– at seeding or newly-seeded cool-season turf
Tupersan (siduron)
Tenacity (mesotrione) – best applied by a lawn
care company
Drive (quinclorac) – certain formulations are for
commercial applicators only
Preemergence Crabgrass Herbicides –
established cool-season turf
Barricade (prodiamine)
Dimension (dithiopyr)
pendimethalin (Halts, Pre-M, Pendulum, etc.)
bensulide (Bensumec, etc.)
Team (trifluralin + benefin)
Dacthal (DCPA)
Balan (benefin)
Tupersan (siduron)
Preemergence Crabgrass Herbicides –
established warm-season turf
Barricade (prodiamine)
Dimension (dithiopyr)
pendimethalin (Halts, Pre-M, Pendulum, etc.)
bensulide (Bensumec, etc.)
Team (trifluralin + benefin)
Dacthal (DCPA)
Balan (benefin)
Postemergence crabgrass herbicides –
cool season turf
Dimension (pre-tillering of crabgrass)
Drive/products containing quinclorac
Acclaim Extra (fenoxaprop)
Tenacity (mesotrione)
Annual Bluegrass control
•Preemergence crabgrass herbicide in late
August (probably will not be able to
overseed)
•No postemergence controls for
homeowners
Preemergence Control
of Annual Broadleaf Weeds
Depends upon the herbicide
Preemergence control possible for:
Spotted (Prostrate) spurge
Common chickweed
Henbit
Others
Preemergence broadleaf control
Gallery, Green Light Portrait (isoxaben)
Preemergence crabgrass herbicides
Bermudagrass Suppression in
Tall fescue
•Suppression/Need repeat treatments
•Acclaim Extra + Turflon, some other
chemicals
•Or 2-3 applications of Roundup and reseed
•Proper mowing height
•Overseeding
Yellow nutsedge control in Cool-season turf
Postemergence
control
- SedgeHammer
- Dismiss
- Basagran
-Also used for
kyllinga control
Wild Onion, Wild Garlic Control
2,4-D ester
Broadleaf Control Chemicals
2,4-D, 2,4-DP, MCPP, MCPA, dicamba,
triclopyr, clopyralid, fluroxypyr
• Usually use combinations such as
• 2,4-D + MCPP
• 2,4-D + MCPP + dicamba
• Leaf, root absorbed
• Sprays and granular forms
Spray versus Granular application
•Spray generally provides better control since
these chemicals are absorbed by leaves as well as
roots
•Granular formulations – reduce potential for leaf
uptake, apply when dew is present
•Granules – no spray drift, still can injure
ornamentals through root uptake
Dandelion
Buckhorn plantain
Oxalis (woodsorrel)
Ground ivy
Triclopyr or a dicamba based product
Wild Violet Control in Turf
Postemergence
control
- triclopyr
based product
Lespedeza
- Use a triclopyr based product
Virginia buttonweed
Repeat applications of a
turf combination
broadleaf herbicide (Trimec, etc.)
Ornamental Bed Weed control
• Cultural Control
• Chemical control
Cultural Control in beds
• Hand-weeding, tilling, hoeing
• Mulches
– Organic : pine bark, pine straw,
hardwood bark, etc
– Inorganic – rocks
– Black plastic
– Landscape fabrics
Mulches
• 2 to 4 depth
• Avoid mulch with a sulfur or ammonia
odor (sour mulch)
• Free of weed seed
• Control annual weeds
• Rock mulches better than bark mulches
for weed control
• Bark mulches can support weed
growth
Black plastic
• Controls annuals and suppresses
perennial weeds (inhbits water
movement, gas exchange)
• Lacks porosity
• Best fit is annuals, vegetable gardens
• Consider fabrics for long-term use
Black plastic
• Improves weed control over mulch
alone
• Lacks porosity (water, gases cannot
readily move through)
• Encourages surface rooting
• Does not hold mulch well
Landscape fabrics
• Allow for water, gas exchange
• Sacrifice on weed control compared to
solid black plastic
• Shoot penetrate upward through fabric
• Root penetration downward through
fabric
• Keep totally covered with 1 inch mulch
• Rock mulches better for weed control
Chemical Weed Control in Ornamentals
• Preemergence herbicides
• Postemergence herbicides
Annual Flower beds
• Site prep – control perennial weeds prior to
planting
• Rototill
• Transplant
• Irrigate
• Apply granular trifluralin (Preen Garden
Weed Preventer, Treflan, etc)
• Irrigate
• Mulch
Woody ornamental beds
• Wider choice of preemergence
herbicides than in annual beds (ie
Snapshot)
• Apply prior to mulching
Postemergence Herbicides Ornamentals
A) Selective herbicides
grasses - Segment, Fusilade/Ornamec
(Grass-B-Gon),
Envoy, Acclaim
yellow nutsedge – Basagran, SedgeHammer
woody orn directed spray
broadleaves - none
Postemergence Herbicides Ornamentals
B) Nonselective herbicides
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Contact
– Reward
– Scythe, acetic acid based products
(BurnOut, etc)
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Contact/systemic- Finale
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Systemic – glyphosate (Roundup, etc)
glyphosate (Roundup, others)
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Off patent, many producers
nonselective systemic
leaf, bark absorbed
inactivated upon contact with soil
use under good soil moisture
wiper or shielded spray applications
Yellow nutsedge
• perennial sedge
• cultural control - landscape fabrics
• chemical control
preemergence – Pennant Magnum,
Tower
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postemergence – SedgeHammer,
Basagran, Roundup, Finale, Reward
Bermudagrass control
Postemergence control in broadleaf
ornamentals and nongrass monocots
like liriope
Fusilade/Ornamec/Grass-B-Gon
Segment
Envoy
Poison ivy
• perennial broadleaf
• postemergence control - nonselective
glyphosate, Finale
• Triclopyr (Brush-B-Gon)
Weed Control in Vegetable Gardens
Cultural
• Hand-weeding, hoeing, cultivation
• Mulches – grass clippings (do not use from
a lawn recently treated with a post broadleaf
herbicide)
• Newspaper + grass clippings
• Black plastic
Weed Control in Vegetable Gardens
• Rototill in spring to control
chickweed and other winter
annuals
Weed Control in Vegetable Gardens
Chemical Control
• Trifluralin (Preen Garden Weed Preventer,
others)
See PMG and label for which species can
be treated at seeding, which at transplanting
• Glyphosate for site prep or after final
harvest