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Outline
Weed Seeds, Tools & Herbicide Families
Integrated Weed Management Weed Management Tools “Many small hammers”
Integrated Weed Management in Vegetable Crops
The “realities” The density of weeds that survive cultivation is directly proportional to the initial density of weeds No matter how many weeds are there at the start, you’ll kill the same proportion In order to deal with weeds (both emerged and those in the weed seed bank) You have to weed more, weed better or start with fewer weeds
Weed Management Tools Sanitation / Prevention Competition Healthy crops
Reduce seed survival Early recruitment Predation Stale seedbed / False seedbed
Crop rotations Prevent weed seed set Weed seedling control Reduce seed germination Cultivators Erode the seed bank Flame weeders Herbicides Etc.
Herbicide Modes of Actions
Integrated Weed Management The key to successful, sustainable weed management is to use many little hammers (or multiple stresses or tools) to knock them down You chip away at them Gradually, over time, you beat them
“Many small hammers” Seed set & seed rain Crop Rotation
Control Predation
Early recruitment Competition
Stale seedbed / False seedbed
Seed decay
Shallow disturbance
Sanitation / Prevention of entry
Deep burial Seed dormancy
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Pre‐empting seed rain
Encourage seed decay
Critical to winning the war on weeds
Misconception = weed seeds last forever
If you can prevent the addition of seeds to the soil, you can reduce the size of next year’s seed bank by 45‐93%
Truth ‐ seed decay = fairly rapid, with most seeds declining within a short time
Encouraging seed germination
Typical half‐life of seeds is less than a year
Encouraging seed germination Disturbance and timing of the disturbance = key
Shallow cultivation Keeping weed seeds near the surface Shallower seed depth increases germination & mortality, decreases dormancy They will be quicker to come up and be controlled Faster drying and dying
Encouraging seed germination Shallow sweeping (cultivation) will do less damage to soil structure than deeper cultivation Combining shallow cultivation with cover crops offsets the negative impact of increased cultivation
Cultivate at different times Encourage germination Gradually deplete the seed bank through the other controls 1‐2 disturbances will provide some reduction (~50%) 3‐4 disturbances can dramatically reduce populations
Encouraging seed predation Do as much as you can to keep the seeds at or near the soil surface Encourages predation by ground beetles and other animals Encourages drying and seed mortality It is highly variable, but can be very effective when it works
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Early season recruitment Refers to encouraging a big flush of early weeds which can then be killed easily Stale seedbed Weeds encouraged to emerge and be controlled prior to crop emergence
False seedbed Multiple cultivations at different intervals
Other tools Sanitation & prevention of entry/introduction Competition Healthy plants Cover crops
Crop rotations Seed dormancy – deep burial Herbicides
Mode of Action (MOA)
MODES OF ACTION
“a functional or anatomical change, at the cellular level, resulting from the exposure of a living organism to a substance” How an active ingredient acts on a pest to control it or prevent damage to the host Relates to specific genetic, metabolic or physical process targets
Why do MOAs matter?
Why do MOAs matter?
Affects what pests a specific product will control
Affects speed and duration of pesticide activity (contact vs. systemic)
e.g. Grassy weeds vs. Broadleaf weeds
Affects what stage of life a pest can be controlled at e.g. pre‐emergence (seed/seedling) vs. post‐ emergence (seedling/top growth)
Relates to how a pest will respond/react e.g. rapid death vs. cessation of growth vs. discolouration and slow death
Affects how quickly/easily a pest can/will develop resistance to a particular MOA (e.g. similar MOAs mean more exposure and increased chance of resistance)
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Herbicide MOAs
HERBICIDE MODES OF ACTION
MOA classification groupings are determined by the Herbicide Resistance Action Committee (HRAC), based on site of action The Weed Science Society of America (WSSA) classifies/groups of herbicides by number
Herbicides relate to all products that have activity on plants Act on plants (weeds) to disrupt specific processes, resulting in eventual death
Herbicide MOA – Light Processes Inhibition of photosynthesis C
D 22
14
Reglone
Aim
5 7 6
E
Inhibition of pigment synthesis (bleaching) F
Command
C – Blocks the transfer of light energy, results in reduced carbohydrate production starves plant
D & E – Disrupts cell membranes to prevent cells from manufacturing food or disrupts membrane integrity (leaky membranes)
28
27
Atrazine / Sinbar / Basagran / Lorox
Different actions:
12
11 13
Avenge
Herbicide MOA – Cell Metabolism Amino acid synthesis Ally / Odyssey
B
G
2
9
Membrane disruption M
Roundup
Different actions:
Different actions:
B – starves plant of amino acids needed for DNA synthesis
Different actions: Blocks accumulation or synthesis of pigments such as chlorophyll and carotenoid Energy can’t dissipate = leaky membranes and cell death
24
Very rapid membrane disruption and death
growth stops, then stunting and death of growing point
G – stops amino acid synthesis (different from Grp2) = accumulation of toxic compounds inhibition of growth, then chlorosis and death
rapid drying and death
Herbicide MOA – Cell Metabolism Lipid synthesis disruption Poast Ultra / Venture
A
N
1
8
Other types of cell metabolism disruption
Eptam
H Liberty 10
Different actions: Grp1 is specific to grassy weeds A – affects production of the lipids needed for membrane formation in cells in the growing points N – affects the processes that maintain the waxy cuticle of seedlings
I 18
Frontline
Different actions: H – inhibits ammonia assimilation in organic compounds, causing accumulation, which reduces photosynthesis and growth rapid chlorosis and wilting
I – inhibits cell division and expansion in growing points slow death of growing points and rest of plant
Herbicide MOA – Growth & Cell Division Inhibition of cell division, microtubule organization assembly Treflan 3
Cell wall (cellulose) synthesis Casoron 20
K
Dual II
15
23
CIPC
Different actions: Inhibits cell division Grp 3 = inhibits root extension, resulting in short, stubby, deformed roots Grp 15 = mostly affects shoot growth (extension) Grp 23 = root and shoot growth inhibition
Gallery
L 21 29
Accord 26 Alion
Different actions: Usually affects roots and shoots Seedling germination and emergence often affected
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Herbicide MOA – Growth & Cell Division Growth regulators / Synthetic auxins O 4
Auxin transport P Distinct
2,4‐D / MCPA / Tordon
Different actions:
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Different actions:
Disrupts balance of auxins in plants, resulting in either uncontrolled cell division & growth (low conc) or restricted growth (high conc) Bending, twisting, distorted growth
AVOIDING RESISTANCE
Auxins accumulate in growing points Stunting or odd growth
Avoiding Resistance Avoid overuse of chemicals Monitor for pests Use economic thresholds Use cultural/biological controls
Rotate/alternate between chemical families / MOA Watch for similar MOA between groups Be careful with multiple MOA products Use tank mixes with care (especially those with similar MOAs)
Avoiding Resistance Ensure that chosen products will be effective at that specific spray timing Use label rates (avoid low rates) Avoid “re‐treating” with same product If products are ineffective
Use products with longer residual (persistent) periods with care Spot treat, when possible Control alternate hosts
Rob Spencer, BSA, MSc, P.Ag. Commercial Horticulture Specialist
QUESTIONS???
[email protected]
Alberta Ag‐Info Centre
310‐FARM
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