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/456/456-018/456-018.html

• Herbicide labels

Additional Information – Weed ID Websites

www.ppws.vt.edu/ipm/weeds_container_nurseries.html

www.turfweeds.net

www.ppws.vt.edu/weedindex.htm

Virginia Tech Weed ID websites

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

• 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

Giant foxtail

Goosegrass

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

Common chickweed Horseweed

Henbit

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

Bermudagrass

Perennial grasses

Quackgrass

Johnsongrass

Yellow and Purple NutsedgePerennial 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

Dandelion Buckhorn plantain

Simple perennial broadleaves

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

• 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 Controlof 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 turfPostemergence 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

• Contact – Reward

– Scythe, acetic acid based products (BurnOut, etc)

• Contact/systemic- Finale

• Systemic – glyphosate (Roundup, etc)

glyphosate (Roundup, others)

• 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

• 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 - nonselectiveglyphosate, 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