WEED CONTROL IN PASTURES

Shayan Ghajar, PhD Student & Pratt Fellow

Virginia Tech

What we’ll cover today

• Definition

• Goals

• Prevention

• Detection/Identification

• Control options

• Hogweed

The definition of a weed

• No scientific definition

• Simply a plant that is somewhere you don’t want it

• There are county and state lists

A Noxious Weed

“A Noxious weed is defined as any living plant, or part thereof, declared by the Board through regulations under this chapter to be detrimental to crops, surface waters, including lakes, or other desirable plants, livestock, land, or other property, or to be injurious to public health, the environment, or the economy, except when in-state production of such living plant, or part thereof, is commercially viable or such living plant is commercially propagated in Virginia. The Noxious Weeds Law provides authority to the Board of Agriculture and Consumer Services (BACS) to add or delete weeds from Virginia’s noxious weeds list.”

http://www.vdacs.virginia.gov/plant-industry-services-noxious-weeds.shtml

A different point of view

• Weeds are “nature’s bandaid” on bare ground

• Usually a symptom more than a cause

• They often tell you a story of a deeper issue

So what do we want in a pasture?

• For grazing:• Optimal nutrition

• Safe plants

• For turnout only:• Stable soil cover

• Also safe plants

Goals

• Maximize useful forage species while minimizing expense

• Efficient management

PREVENTION

Happy grass, fewer weeds

• First line of defense is a happy pasture

• A thick stand of grass will:• Shade out weeds

• Outcompete them for nutrients

• Prevent weed seeds from germinating

Moderation: Grazing and Mowing Height

Adapted from NRCS Bozeman, MT.

Grazing Height

Source: USDA “Pastures for Profit,” Publication A3529http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1097378.pdf

Grass BiologyGrass recovers from grazing if:• Its growing point (apical

meristem) is intact• It has adequate carbohydrate

reserves• It is given adequate time to

regrow after being grazed

Grazing Height

• Graze when fescue is 8-12” tall

• Stop grazing when fescue is ~4” tall

• “Take half leave half”—not always possible, but ideal

Hoof Traffic

• A huge factor in the stresses placed on equine pastures

• Doesn’t just remove leaf area like grazing:• Buries or slices leaves

• Cuts through roots, rhizomes, and sod

• Opens up microclimates for weed seeds in the soil to germinate

Our Grazing System• Continuous grazing system (CG)

(3.7 ha)

• Rotational grazing system (RG) (3.7 ha)• Four grazing lanes (0.71 ha)

• 560 m2 stone dust heavy use area (HUA) & vegetative HUAs

• Each system grazed by four TB geldings • BW 500-615kg

• Ages 4-12 yr

Methods: Grazing• Began grazing RG lanes when

forage was ~10 in tall

• Rotated to the next grazing lane when grazed to stubble height of 4-5 in

• RG and CG mowed to 10 in as-needed to maintain vegetative rather than reproductive state

Ground Cover: RG vs CG

0

20

40

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CG RG CG RG CG RG CG RG

Ground Cover Grasses Legumes Weeds

GR

OU

ND

CO

VE

R, %

Forage Species: RG vs CG

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CG RG CG RG CG RG CG RG CG RG CG RG

Tall Fescue White Clover Bluegrass Orchardgrass Bermuda Crabgrass

GR

OU

ND

CO

VE

R, %

Biomass Yield: RG vs CG

P = 0.07

0

500

1000

1500

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CG RG

Yie

ld, k

g/h

a

Before Grazing vs After Grazing

Summary:

• Happy grass means fewer weeds

• Monitor grazing height closely

• Anticipate seasonal changes

IDENTIFICATION, OR DIAGNOSING A

PROBLEM

Walk your pasture(s)

• How often do you check on your horse?

• When you turn out your horses, follow them into the pasture

• Walk in a zigzag pattern across the field(s)

• Stop to collect plants you can’t identify

• Start with the most plentiful

• Gradually work your way down to the more rare specimens

Evaluating your pasture

• If you are hitting a lot of bare ground and ~30% non-grass species, time to change management strategies

• If you hit lots of grass, you are likely managing well, BUT:• Keep an eye out for dangerous

plants

Plant Identification

• Multiple approaches• Learn botany

• The simpler approach:

1. Take multiple pictures, or a whole-plant sample

2. Send pictures or take sample to Extension

Caution: Google or Facebook ID

• Unreliable

• Like diagnosis for disease online

• One group is the exception: Virginia Native Plant Society Discussion

Life cycles matter a lot!

• Annual weeds are typically easier to manage

• Perennials get a foothold and may be hard to dislodge

CONTROL

Four options

• Change management

• Herbicides

• Mechanical/hand thinning

• Live with it

When is management enough

• Short-lived weeds

• Not dangerous

• Pastures will bounce quickly with rest or rotational grazing

• Or soil amendments will address the issue

Herbicides

• Herbicides are usually the most effective option for perennial weeds

• Many varieties for many different plants

• Some require licenses; all require knowledge of use

• LABELS

• Some are selective, some hurt all plants

Spot spray vs broad application

• If you can tote a backpack or pump sprayer around and the weeds are not too abundant, that’s the cheaper route

• If they are abundant or you are unable to tote heavy weights around, broadcast is better

Next steps:

1. Identify problem weeds to Extension or contractor with pesticide license

2. Get expert input

3. If DIY seems advisable, read labels multiple times, learn about legal and environmental aspects of herbicide use (drift, etc)

4. If DIY impractical (usually the case) call a contractor

Notes on herbicides

• Be wary of rain or overcast days

• Wind can cause drift

• Be aware of environmentally sensitive areas

• Laws regulating wetlands and waterways

• Be a good neighbor

• Never use off-label

Mechanical control

• Mowing• Height

• Watch your grass!

• Season

• Repeated mowing usually needed

• Hand weeding• Ouch, basically

Live with it

• If it isn’t poisonous and it isn’t increasing and it isn’t costing you money,

HOGWEED

Quick Summary

• Invasive from Eurasia

• Sap causes burns and blindness if it touches your skin

• It cannot chase you

• Plant ID prior to cutting things down is advised

ID

• https://www.dec.ny.gov/animals/72766.html

SOME COMMON WEEDS

Buttercup Ranunculus spp

Potential for Toxicity: Low. Toxic when dry? No. Clinical Signs: Oral and gastrointestinal irritation and blistering. Treatment: Recovery is uneventful when animals removed form source.

Curly Dock Rumex crispus

Potential for Toxicity: Moderate. Toxic when dry? N/A Clinical Signs: Muscle tremors, weakness, depression, and recumbency. Treatment: Intravenous Ca, Mg, glucose, electrolytes. Oral limewater.

Groundsel/ragwort Senecio vulgaris

Potential for Toxicity: Extremely high. Toxic when dry? Yes. Clinical Signs: Liver disease, photo-sensitization, weight loss, and jaundice. Treatment: Once liver damage is done, treatment is unsuccessful. Humane euthanasia recommended.

Water Hemlock Cicuta maculata

Potential for Toxicity: Extremely High. Toxic when dry?Yes. Clinical Signs: Signs include convulsions and death due to respiratory failure. Treatment: Due to rapid reaction, veterinary intervention is unlikely. In some cases Sodium Phenobarbital may help.

Yew Taxes spp.

Potential for Toxicity: Extremely High. Toxic when dry? Unknown. Clinical Signs: Within one hour of ingestion trembling. Death within 15 minutes of appearance of clinical signs. Treatment: Supportive therapy including activated charcoal and saline cathartic. Atropine to counter depression.

Tall fescue festuca arundinacea

Potential for Toxicity: Moderate. Toxic when dry? Yes. Clinical Signs: Toxic effects in broodmares only, including prolonged gestation, retained placenta and agalactia. Treatment: Remove the mare form fescue for the last 30-90 days prior to expected foaling date. Treatment with oral Domperidone at least 15 days prior to expected foaling date.

Johnson grass Sorghum halepense

Potential for Toxicity: Moderate.Toxic when dry? Cyanide – no; Nitrates – yes.Clinical Signs: Rapid breathing, tremors, frequent urination, defecation, gasping and convulsions.Treatment. Supportive drug therapy can offset the effects of less severe cyanide poisoning.

Fall Panicum Panicum dichotomiflorum

Potential for Toxicity: High.Toxic When Dry? Yes.Clinical Signs: Hepatotoxic to horses, weight loss, jaundice, colic, diarrhea, and fever.Treatment: Immediate withdrawal of Panicum should allow all but severely affected animals to recover from acute exposure

Red Maple Tree Acer rubrum

Potential for Toxicity: High.Toxic when dry? Yes. Clinical signs: Massive destruction of red blood cells leading to breathing difficulties, jaundice, dark brown urine, and death.Treatment: Supportive therapy, (50-75% death/euthanasia rate).

Cherry Prunus spp.

Potential for Toxicity: HighClinical Signs: Breathing difficulties, anxiety, staggering, convulsions, collapse, and death, within minutes of ingestion Treatment: If horse is alive after 2-3 hours, chances are good it will recover. Veterinary treatment includes intravenous administration of sodium thiosulfate and sodium uirite.

Black Walnut Juglans nigra

Potential for Toxicity: Moderate.Toxic when dry? Yes.Clinical Signs: Horses bedded on shavings containing 20% more black walnut develop severe laminitis, limb edema and colic within 12/18 hours. Treatment: Remove the bedding, treat the clinical signs.

Black Locust Robinia pesudoacacia

Potential for Toxicity: Moderate. Clinical Signs: Colic, constipation, diarrhea, muscle weakness, laminitis and irregular heartbeat may occur within one hour of eating; Fatalities are rare. Treatment: Prevent further ingestion and treat clinic signs.

Oak Quercus spp.

Potential for Toxicity: Moderate. Toxic when dry? Unknown. Clinical Signs: New young leaves and green acorns most toxic leading to poor appetite, weight loss, diarrhea or constipation, increased drinking, increased urination, death is possible.Treatment: Aggressive fluid therapy and low stress environment.

Nimblewill (pie plate grass)

• Perennial with stolons

• Stems are branching forming thick mats. Roots at the nodes.

• Stems and stolons die back in fall

Green/Yellow Foxtail

• Clump forming summer annual

• Prolific seeder

• Often mistaken for desired species

Crabgrass

• Several species

• Summer annual

• Prostrate and upright growth

• Prolific seeder

White Dutch Clover

• Perennial

• Low growing, prostrate

• Tolerates close grazing

Broomsedge

• Perennial

• Clump forming

• Short rhizomes

• Usually unnoticed until fall

Stickweed (Crownbeard)

• A perennial that may reach 13 feet

• Stems have wings

• Basal crown from which new plants can arise

Ironweed

• Perennial with a basal crown from which new plants arise.

• Purple flowers

• Leaves 4-10 inches long with small teeth along the margin

• Ironweed because stems stay erect through winter

Bull Thistle

• Biennial

• Taproot

• Leaves are hairy

• Rosette when young

Horsenettle

• Perennial

• Spines on leaves and stems

• Can reach 3ft tall but will flower at much lower heights

• Leaves smell like potatoes when crushed

• Poisonous to livestock

Spiny Amaranth

• Summer annual

• Spines at petiole and stem

• Compacted, disturbed or worn areas

• 100,000 seeds per plant

• Continuous flushes

Jointhead Arthraxon

• Annual

• Low growing

• Prefers moist areas

• Confused with Japanese Stiltgrass, Asiatic Dayflower, and Deer-tongue

Autumn Olive

• Woody shrub

• Ornamental that has escaped

• Red berries in fall

• Birds love