Knockdown Control of Difficult Weeds : Fleabane, Melons & Grasses

Multiple tank mixes are becoming increasingly prevalent, particularly for pre-plant and early post emergent applications where getting across large areas in a timely manner is critical.

Unfortunately water is often not a great carrier for agricultural chemicals as it is a charged polar molecule and variability in water temperature and quality can affect how well products dissolve into it. When the cost of product in a spray tank is considered, it pays to ensure that they are mixed correctly.
Most agricultural chemicals are formulated to be as emulisifiable as possible, but many contain elements that either do not dissolve well (wettable powders – WP’s and water dispersible granules – WDG’s), petroleum distillates (emulisifiable concentrates – EC’s) or just precipitate, as they are heavier than the water (fertilizers, powdered metals, etc). Care should be taken when using these, particularly when under time constraints.

This technote describes correct mixing techniques to optimise active ingredient activity by maintaining them in suspension in the spray tank during the entire spray operation. Adjuvants and compatibilisers such as N-Flow® play a major role in bonding the otherwise unmixable spray materials with water.

Fleabane Control – Key Findings

• In glyphosate tank mixes, high emulsifier loaded mineral oils – such as ENHANCE® or ANTIEVAP® at 1% – provide a balance between leaf surface coverage and penetration, enabling effective coverage and translocation, and proved superior to other types
• Glyphosate activity can be reduced by the presence of Ca and Mg ions in hard water – the addition of Ammonium Sulphate will alleviate this.
• A double knock within 7-10 days of the initial application can double the efficacy of the initial treatment and prevent seed set.
• On difficult to control, stressed weeds, a penetrant type mineral oil such as ANTIEVAP® proved the most effective mix partner with paraquat in the double knock, being superior to non-ionic surfactants.

Takeaway Messages

1. For the majority of difficult knockdown weed control situations which include glyphosate, a coarse emulsion mineral oil with droplet survival and penetrant properties such as ANTIEVAP® or high emulsifier loaded mineral oil with spreading properties such as ENHANCE®, provides the best balance of droplet survival, leaf surface coverage and penetration, resulting in more complete weed control.
2. In a paraquat double knock – under difficult conditions or on stressed weeds a penetrant type mineral oil such as ANTIEVAP® will improve the effectiveness of the double knock.
3. Soyal phospholid based products such as COHORT® 700 were of benefit only in hard water situations in mixtures with Glyphosate.

References

• T Boyes AgVivo Agronomy, York Feb 15
• T Boyes AgVivo Agronomy, Quairading Dec 2014