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 html Herbicide labels

Additional Information – Weed ID Websites 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) ryegrassAnnual 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 chickweedHorseweed 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 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

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 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 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 - 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