Lecture 7

LO6 Objectives: - Describe herbicide and insecticide injury symptoms. - Define pesticide injury in non-target species. - List symptoms of pesticide injury in non-target species. - Discuss pesticide injury mitigation strategies.

Reference Material: Section 5 of the Crop Diagnostic Handbook.
Factors Leading to Pesticide Injury: - Incorrect mixing of herbicides. - Insufficient rinsing of application equipment, leading to residue contamination. - Incompatible or incorrect tank mixes that result in synergistic effects or decreased efficacy. - Incorrect application rates. - Applying at the incorrect growth stage of crops. - Drift of herbicide onto adjacent crops, causing unintended exposure. - Use of susceptible crop varieties that are more prone to damage. - Presence of incompatible soil types affecting herbicide effectiveness. - Herbicide carryover from previous seasons due to dry conditions. - Additional stressors (e.g., drought, nutrient deficiencies) that increase crop susceptibility.

Purpose: Tank mixing allows for the application of multiple products in one operation, potentially combating herbicide resistance.

Synergism: - Defined as an interaction where the combined effect of products is greater than the sum of their individual effects, leading to increased crop damage.
Antagonism: - Defined as an interaction reducing the effectiveness of one or more products when mixed, though not directly causing crop damage.
pH effects: - For example, the fungicide Captan has a half-life of 3 hours at pH 7.1 and only 10 minutes at pH 8.2.
Incompatibility of Active Ingredients: - Some active ingredients may become less effective or inactivated when mixed with certain adjuvants, like glyphosate being tied up by Metribuzin.
Uptake/Retention Issues: - Certain combinations of herbicides may lead to one product inhibiting the effectiveness of another, such as a contact herbicide damaging foliage before systemic absorption occurs.

Label Compliance: - ALWAYS read and follow labels for compatibility and specific mixing instructions.
Order of Mixing: - Follow the WAMLEGS principle for mixing order: - W: Wettable powders, flowables. - A: Agitate and anti-foaming compounds/buffers. - M: Microcapsule suspensions. - L: Liquids and solubles. - E: Emulsifiable concentrates. - G: High-load glyphosates. - S: Surfactants.

Residual Damage Prevention: - Residues from spray equipment can cause damage to different crops, necessitating proper cleaning procedures: - Drain the equipment after use. - Rinse with 100-150L of clean water, ensuring thorough procedures: - Perform 3 rinses with clean water. - Do not allow pesticide residues to dry on tank walls or plumbing.

Immediately after spraying: If immediate cleaning is not possible, spray inside the tank with clean water.
Fill the sprayer with at least 1/10th of spray tank volume (100-150L).
Completely drain the tank.
Use clean water to rinse all parts of the spraying equipment, ensuring to flush boom ends.

Remove filler screens and check for residues.
Clean residues using a soft brush and appropriate cleaning solution.
Inspect the inside of the tank for residues, paying close attention to the tank roof.
Use a cleaning solution at a volume of at least 1/10th the tank size, agitate for 15 minutes.

Moisture Requirement: Adequate moisture from rainfall is crucial for the breakdown of herbicides; insufficient moisture increases carryover risk.
Risk Assessment: - Evaluate fields for potential carryover before planting subsequent crops. - Herbicide residues can cause damage, particularly in sensitive crops if not properly managed.

Extreme (<50 mm rainfall)
Serious (<75 mm rainfall)
Very High (<100 mm rainfall)
High (<125 mm rainfall)
Moderate (<150 mm rainfall)
Uncertain (<160 mm rainfall)
Normal (≥160 mm rainfall)
In-season rainfall significantly affects herbicide degradation in soil. Areas that receive below-average precipitation may suffer from increased herbicide stability, raising the risk of crop injury in future seasons.

Follow label directions closely for safe re-cropping options following residual herbicide application.
For crops in high-risk areas or after applying certain herbicides, contact the manufacturer for advice on suitable rotational crops.

Deactivation Processes include: - Microbial action: The primary method where soil microbes degrade herbicides. - Chemical hydrolysis: Breakdown by water leading to less active derivatives. - Volatilization: Loss of herbicides as gases. - Photo degradation: Breakdown due to light exposure. - Binding to Soil Particles: Reducing bioavailability.
Higher organic matter content generally leads to lower carryover risks.

Agronomic Practices: - Implementing crop rotation to diversify planting selections helps mitigate herbicide carryover risk. - Choose less sensitive crops during high carryover risk years to avoid damage from remaining residues. - Employ best practices for crop stress management to minimize herbicide impact. - Delayed Seeding: Postponing planting may facilitate natural degradation of residues due to spring rains and optimal temperatures.

Herbicide Breakdown: Primarily influenced by moisture, temperature, and time, with various other environmental factors contributing to degradation levels.
Group 2 Herbicides (Imidazoline family) such as imazamox and imazethapyr carry significant carryover risks, particularly for crops planted immediately following application.
Some new product labels have been updated following climate extremes experienced in 2021.
Utilize multiple tools for assessing herbicide carryover risk, and recognize that while mitigation strategies can reduce risk, they do not completely eliminate it.