j. ferrell extension weed specialist of onsite ppts...don’t assume your herbicide will kill every...
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Why herbicides fail
J. Ferrell Extension Weed Specialist
Where we are today
• Herbicides are more potent and forgiving than ever before.
Why do herbicides fail?
• Generally speaking, applicator error.
• Not going to discuss improper calculation, rain-off, or forgetting to add the herbicide to the sprayer.
Don’t assume your herbicide will kill every weed
• Milestone VM controls many weeds, but not all of them:
Tropical soda apple - yes Blackberry - no
James H. Miller. USDA Forest Service. Invasive Plants of the Eastern United States CD-ROM
Plant Size
Application timing
• Annuals – germinate from seed, produce seed, die within 1 yr. – Spanish needles, ragweed, etc.
• Perennials – emerge from rootstock, produce seed, go dormant. – Blackberry, trees, etc.
Annual
Control of Annual Weeds
0
20
40
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80
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120
Emerg. Seed. Veg. Flower Mat.
Wee
d C
ontr
ol
Perennials Control of Perennial Weeds
0
10
20
30
40
50
60
70
80
90
100
Dorm. Veg. Bud Flower Fruiting Fall
Wee
d C
ontr
ol
Drought
• Slow plant growth. More time for the plant to disassemble the herbicide.
• Cuticle thickness.
Adjuvants
• Can greatly improve herbicide uptake
Leaf Surface
No adjuvant
adjuvant
Reduction of Droplet Surface Tension
Surfactants vs Oils
• Surfactants simply flatten out the droplet.
• Oils (methylated seed oils) will partially dissolve leaf waxes.
Why not use MSO all the time?
• Surfactant - $5 per 100 gal water
• MSO - $10-20 per 100 gal water
Application technique
• More is not always better.
More is not better
100% spray retention 30% spray retention
Why do they fail?
• Misidentified the weed • Wrong herbicide • Weed size • Application timing • Adjuvant selection • Drought • Improper spray technique
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