2023 What influences herbicide performance?
Or how to stop wasting $$
Useful links
Adjuvants
Pre emergents 1, 2, 3
1. Adsorption: Some of the herbicide gets adsorbed onto the soil, making it less mobile.
2. Degradation: Over time, natural processes like photodegradation and, moisture, breaks down the herbicide.
3. Soil pH
4. Temperature
5. Rainfall
6. Moisture
7. Humidity
For a herbicide to work it needs three things:
Good contact
Poor contact will give poor results.
Length of contact
If it isn’t in contact for long. Poor results.
Site of action
Must be able to move to where it actually works.
Hairy and waxy leaves can impact on herbicides
Rain after application
Actively growing
Soil Factors ● CEC ● Organic matter ● Texture ● pH Climatic Factors ● Humidity ● Temperature ● Amount of light ● Moisture
Challenges deep-dive
CEC
Injury symptoms caused by the residual effect of oxyfluorfen on sorghum. Injury symptoms caused by the residual effect of oxyfluorfen on sorghum at 0, 15, 30, 45, 60, 90, 120, 150, 180, and 200 days after application (DAA) of the herbicide in comparison with the control treatment (C), in soils in the region of Curitibanos-SC: Ultisol (clay), Rio
Paranaíba-MG: Oxisol (clay), and Oratórios-MG, Brazil: Inceptisol (loamy sand).
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soils ability to adsorb positively charged compounds
fine-textured, high-organic matter soils have larger CEC’s than coarse, low-organic matter soils
influences water solubility, adsorption, and hydrolysis
triazines
sulfonylureas
Imidazolinones
glyphosate
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pH
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Temperature
Couch grown at high temperatures retains 3x more glyphosate than at low temperatures.
In general, uptake and translocation of foliar herbicides increases with increasing temperature
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Pre-emergent herbicides can vary dramatically in how they behave after rainfall
Rainfall ●
Active Water Solubility (mg/L) Soil Adsorption Capacity Koc Soil Movement/ Leaching Rating S-metolachlor 530 100 High Pendimethalin 0.275 25455 Very Low Prodiamine 0.013 13000 Very Low Propyzamide 15 200 High
Soil moisture
Crowsfoot control increases with increasing soil moisture
Best at > 20% VMC and lowest at < 12% VMC.
Diclofop activity reduced at low soil moisture
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Humidity
RH effects glufosinateammonium
Best results under high RH
Use an adjuvant in low RH conditions.
Potential for spray freight increases
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Light
A 44% loss in 3 days due to photodegradation of some preemergent herbicides, when used on bare soil and not watered in.
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In a turf setting, 10% loss was within 7 days when not watered into the turf.
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Pre emergents 1, 2,
Adjuvants
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