6.6.C: Herbicides and Pesticides

6. Weed and pest control at sowing: List

• Herbicides

• Insecticides

Weeds and Herbicides: Approaches to use

• Total control

• Selective control

Total Control: Meaning

For complete control of weeds prior to sowing

Selective Control: Meaning

For control of target weeds in established pastures

8. Post-sowing management: Monitor

• Monitor for volunteer weed invasion, be ready to spray if needed

8. Post-sowing management: Grazing

Light grazing 8-10 weeks after sowing, based on growth and plant anchoring

8. Post-sowing management: Timeline

• Year 1: Graze frequently but gently: Light into the pasture base without harming young plants

• Year 1 - Year 3: Increase production gradually

• Year 3: Full capacity

Treatments used in pasture improvement

• Herbicide Treatments

• Winter Cleaning

• Spray topping

• Spray grazing

Pasture Improvement: Herbicide Treatments

• Controls pasture population

• Used sparingly to avoid herbicide resistance

Winter Cleaning: Chemicals

1-1.5 L/ha simazine + 0.2 L/ha paraquat

Winter Cleaning: Application and why

6-10 weeks after autumn break: Pasture species not affected at this stage, while small grass seedlings are

Winter Cleaning: Grazing

Winter grazing on treated pastures is reduced

Spray Topping: Aim

Sterilise seeds of annual grasses using glyphosate or paraquat after seedheads emerge

Spray Topping: Timing

Apply glyphosate as soon as all seedheads have emerged, paraquat is applied slightly later

Spray Topping: Preference

Glyphosate preferred for barley grass and mixed infestations due to timing flexibility

Spray Topping: Benefits

Glyphosate enhances pasture palatability, improving dry feed utilisation

Spray Topping: Caution

Using wetting agents may risk damage to perennial ryegrass and phalaris

Spray Grazing: Application Method

Use hormonal chemicals to induce upright growth in weeds, followed by heavy grazing to consume affected plant material.

Spray Grazing: Effective Against

Broadleaf weeds

Spray Grazing: Herbicide Choice

• White Clover or both: 2,4-D amine

• Subclover: MCPA

Spray Grazing: Timing

Apply 6-8 weeks after weed germination when weeds are actively growing, and clovers have at least 4 true leaves.

Spray Grazing: Grazing Strategy

Graze heavily 7-10 days later with a higher stocking density to reduce pasture cover. Bare-out the pasture within 2-4 weeks.

Spray Grazing: Recovery

Resume normal grazing after the pasture recovers

Spray Grazing: Expectations

Anticipate reduced winter grazing in the year of treatment

Herbicide Treatments: Method

Application of herbicides to control or eliminate weeds.

Herbicide Treatment: Advantages

• Effective at targeting specific weed species.

• Can be used year-round.

• Minimal impact on desirable plants.

Herbicide Treatment: Disadvantages

• Chemical use may have environmental and safety considerations.

• Resistance development in weed populations is a concern.

• Costs associated with purchasing and applying herbicides.

Winter Cleaning: Method

Mechanical or manual removal of weeds during the winter season when crops are not actively growing

Winter Cleaning: Advantages

• Reduces weed seed bank for the next growing season.

• Can be a non-chemical and environmentally friendly method.

• Can be combined with other cultural practices.

Winter Cleaning: Disadvantages

• Labor-intensive and time-consuming.

• May not fully control perennial weeds.

• Timing and weather conditions can affect effectiveness.

Spray Topping: Method

Application of herbicides to the tops of mature weeds to prevent seed production while leaving the rest of the crop or pasture intact

Spray Topping: Advantage

• Targets seed production, reducing weed seed bank.

• Minimal impact on desirable plants.

• Can be used in combination with other weed control methods.

Spray Topping: Disadvantage

• Timing is critical for effectiveness.

• Some herbicides may not be suitable for certain crops or pastures.

• May not control weeds with deep root systems.

Spray Grazing: Method

Allowing livestock to graze on weeds treated with herbicides, effectively consuming the weed material.

Spray Grazing: Advantages

• Provides weed control and utilises livestock for forage.

• Can reduce seed bank and weed regrowth.

• Integration of weed management with livestock farming.

Spray Grazing: Disadvantages

• Requires careful planning to avoid overgrazing

• Risk of herbicide residues in forage, which can impact livestock

• Compatibility with specific herbicides and grazing practices must be considered