sarah kenyon agronomy specialist 417-778-7490...

Sarah Kenyon Agronomy Specialist

417-778-7490 University of Missouri Extension

Resources Extension Office Internet

• USDA Plants Database ohttp://plants.usda.gov

• University Weed Websites oMissouri ohttp://weedid.missouri.edu/

oArkansas o http://www.aragriculture.org/forage_pasture/plant_id/grasses/ o http://www.aragriculture.org/forage_pasture/plant_id/weeds/

oVirginia Tech ohttp://www.ppws.vt.edu/weedindex.htm

Literature • Dichotomous Keys • Regional Books

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1. Cultural Control

2. Mechanical Control

3. Biological Control

4. Chemical Control

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Weed Control

Cultural

Mechanical

Chemical

Biological

Cultural Control • Soil Fertility • Reseeding • Crop Rotation • Timed Planting & Harvesting • Purchasing Certified Seed

Mechanical Control • Mowing or Grazing • Prevents Seed Production • Depletes Carbohydrate Reserves of Perennials

Biological Control • Organism found in nature • Usually specific to target plant • Some Commercially Available

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Removal of legumes White Clover Alfalfa Red Clover Birdsfoot Trefoil

Some herbicides have longer legume replant intervals which needs to be considered before you spray for weeds.

Life Cycle Application Timing Summer Annual • Young and Actively Growing

• April to July Winter Annual • Young and Actively Growing

• November to March Biennial • Rosette Stage

• November to March Perennial • Growth stage dependent

• Young and Actively Growing

Herbicide Application Timing

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Removal of legumes White Clover Alfalfa Red Clover Birdsfoot Trefoil

Some herbicides have longer legume replant intervals which needs to be considered before you spray for weeds.

Herbicide Application Timing

• Your goal is to control the plant when it is actively growing • Young plants that are growing quickly are

more likely to take up the herbicide

• Plants also need to be as healthy as possible before control is applied • Do not brush hog before or after herbicide

applications 6

Removal of legumes White Clover Alfalfa Red Clover Birdsfoot Trefoil

Some herbicides have longer legume replant intervals which needs to be considered before you spray for weeds.

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Surfactants – allow better herbicide coverage by reducing surface tension of the water Check label to determine if one is needed

ALWAYS read the label

Without a surfactant With a surfactant

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Surfactants – allow better herbicide coverage by reducing surface tension of the water Check label to determine if one is needed

Water Conditioners – may be needed if the water in the mix has an incorrect pH or if the water is hard

ALWAYS read the label

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Many herbicides have grazing, haying, and replanting restriction

ALWAYS READ THE LABEL!

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Sericea Lespedeza Horsenettle / Bullnettle

Thistles Brambles

Black Locust Perilla Mint

Spurges Spotted Knapweed

Most Troublesome Weeds in Pastures:

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Perennial legume native to Asia

Prolific seed producer Allelopathic

2 pts PastureGard has been the most consistent treatment across all years of research, regardless of application timing.

Cimarron or Remedy can also be used Source: Dr. Kevin Bradley, MU 12

Perennial Resistant to grazing

spines present

Fertility Frequent mowing Herbicides

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Grazon P+D, GrazonNext, Forefront, Milestone, Surmount, or Tordon 22K

Apply at mid-bloom through fruiting

Control will take multiple years due to prolific seed production. Spray for 3 consecutive years to

achieve 90 – 100% control.

Horsenettle

Biennial or Perennial Rosettes

90% of life span Spines deter grazing Reduces pasture yield by

23% if left uncontrolled

Musk Thistle Bull Thistle

Teasel Tall Thistle 24

Mow within 2 days after the terminal flower head blooms.

Problem Flowers over a 7-9 week period Seed begins to spread about 10 days after first bloom

Multiple mowing may be necessary 11% killed by single mowing at late bud stage 79% killed by second mowing 4 weeks later

Source: Dr. W.H. Fick, KU 25

Spray during rosette stage, fall or early spring

Cimarron, Cimarron Max, Banvel, Grazon P+D, Milestone, GrazonNext, Forefront, PastureGard, Surmount, Trodon 22K, or 2,4-D

Do NOT spray during flowering

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Flower head weevil introduced from Europe in 1975

Rosette weevil from Italy introduced in 1979

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1975

1985 Introduction of

flower head weevil

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Thistle Control

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Treat at this stage

Bull Thistle Musk Thistle

Too late to spray

Upright growth

Fertility Mowing Herbicide Application

Full Bloom: PastureGard, or 2,4-D Ester + Remedy Ultra

After Bloom: Metsulfuron, Cimarron Max, Surmount, or Remedy

Source: Dr. Kevin Bradley, MU 32

Prostrate growth

Fertility Mowing Herbicide timing is best in

the fall compared to full bloom October

Cimarron, Cimarron Max, Chaparral, or Remedy

Source: Dr. Kevin Bradley, MU 33

Source: Dr. Kevin Bradley, MU 34

Source: Dr. Kevin Bradley, MU 35

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Dewberry

Do not mow during the year of herbicide application

Regardless of herbicide choice, plan on making a follow up treatment the following year to control escape canes

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Legume, long curling

pea pod Many thorns, 3 points

or more

Multiple mowings Small sprouts

Grazon P+D total coverage of the leaves is needed

Large trees Basal Bark treatment

with Pathfinder II Cut Stump treatment

with Tordon RTU

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Found in moist areas along streams or wooded areas

Mint odor Poisonous to all livestock

Contain ketones that cause acute respiratory distress syndrome

All plant parts poisonous, even in hay

Mowing Grazon P+D, Weedmaster,

or Remedy Apply when plant is

actively growing - late April to early June Before 12 inches tall

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Nodding Spurge Spotted Spurge Tropic Croton Wooly Croton Snow on the Mountain Others

#1 pasture weed complaint throughout the “fescue belt” in late summer 2010 - Kevin Bradley State Weed Scientist

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Nodding Spurge (Chamaesyce nutans (Lag.) Small)

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Spotted Spurge (Chamaesyce maculata (L.) Small)

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Tropic Croton (Croton glandulosus var. septentrionalis Müll. Arg.)

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Wooly Croton (Croton capitatus Michx.)

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Snow on the Mountain (Euphorbia marginata Pursh)

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Poisonous Most contain milky sap

All sap is poisonous when ingested Large quantities must be consumed Pain and swelling of the oral mucosa, blistering and

open sores may be present Toxin is present even in hay

Inspect hay produced late summer and fall for the presence of spurges

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Frequent Mowing Fertility Cimarron, Cimarron Max, Chaparral,

Grazon P+D, GrazonNext, or Dicamba mixed with 2,4-D

2,4-D amine can be used early in the year when the plants are less than 12 inches tall

Spray timing is important summer annual – late summer

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Biennial with a deep taproot

Allelopathic (catechin) Prolific seed production > 50% of seed remained

viable after burial in the soil for 5 years

(Davis et al., 1993) An estimated 63%

reduction in cattle grazing capacity in Montana

(Butcher, 1984)

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0

50

100

150

200

250

300

350

400

450

0 2 4 6 8 10 12 14 16 18 20

Grass

Spotted Knapweed

Years

Plan

ts/m

2

Graph adapted from: Sheley and Jacobs. Weed Technol. 1997: 11:363-368. 60

1 pt/A Tordon 22K 5 oz/A Milestone

Chemicals will provide

control for 2 -3 years but spotted knapweed will reinvade the area unless other control techniques are adopted Montana State University &

Colorado State University Photo Courtesy of:

University of Arkansas

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Irrigation to allow the forage to outcompete the knapweed Not tolerant of flooding or shade

Grazing Colorado State University found that cattle grazing

diffuse knapweed twice during the spring decreased seed production by 50%

Mowing alone is not recommended. The plant can produce seed below the mowing height.

For small areas hand pull/dig plant making sure to remove as much root stock as possible 62

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Source: Dr. Kevin Bradley, MU 71

Source: Dr. Kevin Bradley, MU 72

Identification: 3 stripes on side and 1 orange stripe with dots on the 4 abdominal prolegs

Control when 4 or more ½ inch worms per square foot Hay or Graze Sevin, Mustang Max, Success, or Voliam Xpress Sensitive to natural parasites in wet conditions

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Identification: 4 black dots forming a square on the abdomen and an inverted Y on the head

Control when 4 or more ½ inch worms per square foot Hay or Graze Sevin, Mustang Max, Success, or Voliam Xpress

Photo credit: Bastiaan (Bart) Drees 76

• Alfalfa Weevil • Average of 1 or more larvae per stem and 30% or more

of the plant terminals show feeding damage • Potato Leafhopper

• Resistant Varieties • 0-3” – 0.2 ave. / sweep (0.6 for resistant varieties) • 6” – 0.5 (1.5) • 8-10” – 1.0 (3.0) • 12-14” – 2.0 (6.0)

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• Potato Leafhopper • Aphid • Bacterial Wilt • Verticillium Wilt • Fusarium Wilt • Phytophthora Root Rot • Root Knot Nematode

See alfalfa.org for unbiased ratings *Select dormancy class first*

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• Identify pest • Select the right product • Time the application correctly • Apply accurately • Follow grazing and haying restrictions • ALWAYS READ THE LABEL

Keys to Pesticide Use

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Incorporate… – Mowing/ Grazing – Fertilization – Biological – Herbicides

……in an integrated approach to management

Weed Control

Biological

Mechanical

Chemical

Cultural

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