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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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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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