AVOCADO GROVE APPLICATION GUIDE
Biogenic Amorphous Diatomaceous Earth (−2mm)
Phytophthora Root Rot Management | Soil Silica Amendment
Quick Reference
| Product | BSiO2 Non-Calcined Biogenic Amorphous DE (−2mm) |
| Application Method | Belt spreader — broadcast under canopy drip line |
| Recommended Rate | 200–400 kg per hectare per application |
| Timing | Apply before a rain event or scheduled irrigation |
| Frequency | 2–3 applications per year; increase during wet season |
| Target Zone | Under drip line — avoid direct trunk application |
| Compatibility | Suitable for use alongside phosphonate programmes |
| Shelf Life | Indefinite when stored dry |
How BSiO2 DE Works in Avocado Soils
BSiO2 DE is a non-calcined biogenic amorphous silica sourced from freshwater diatom deposits on the Atherton Tablelands. Unlike calcined (heat-treated) DE, it retains high water solubility — meaning it breaks down readily in moist soil and releases plant-available monosilicic acid (H₄SiO₄).
In avocado groves, this matters for three reasons:
- Immune priming (SAR): Soluble silica is taken up by avocado roots and triggers systemic acquired resistance (SAR) — a natural defence response that makes the tree significantly more resilient to Phytophthora cinnamomi infection.
- Zoospore suppression: Elevated silica in soil solution reduces the mobility and viability of Phytophthora zoospores — the primary infection mechanism in wet conditions.
- Soil structure: Fine DE particles improve drainage and aeration in clay-heavy soils common on the Tablelands, reducing the waterlogged conditions Phytophthora thrives in.
Why non-calcined matters: Most commercial DE is heat-treated (calcined), which drastically reduces its solubility. BSiO2 DE is non-calcined, meaning silica is released rapidly into the soil solution — making it far more bioavailable to your trees.
Application Instructions
Step 1
Calibrate Your Belt Spreader
- Set spreader to deliver 200–400 kg/ha as a starting rate
- For mature trees (>5 years), apply at the higher end of the range
- Conduct a test run on a small section and weigh output before full application
Step 2
Apply Under the Drip Line
- Spread evenly from approximately 0.5m out from the trunk to just beyond the canopy edge
- Do not concentrate product directly against the trunk base
- Feeder roots — the primary uptake zone — sit just below the surface under the canopy
Step 3
Time Application to Moisture
- Apply immediately before a rain event or scheduled irrigation
- Moisture is essential to dissolve the silica and move it into the root zone
- Avoid applying to already waterlogged ground — wait for soil to partially drain first
Step 4
Combine with Phosphonate if Required
- BSiO2 DE is not a direct fungicide — it works by strengthening the tree's natural defences
- For active Phytophthora infection, combine with a registered phosphonate programme (e.g. Agri-Fos trunk injection or Phosgard foliar spray)
- DE + phosphonate together provides both immune priming and direct pathogen inhibition — a proven complementary approach
What to Expect
BSiO2 DE is a soil amendment, not an instant treatment. Results develop over weeks to months as silica is taken up by the root system and plant immunity is gradually primed.
Indicators of a positive response over one growing season may include:
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Improved canopy density and leaf colour
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Reduced dieback in susceptible trees
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Healthier feeder roots on inspection
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Reduced new infection spread across the grove
Tip: We recommend recording tree condition with photos and canopy notes before the first application. This allows a clear comparison over time and helps track the value of the programme.
Storage & Handling
- Store in a dry location away from moisture — clumping reduces spreadability but does not affect efficacy
- Non-toxic and food-grade safe — no special PPE required beyond standard dust precautions
- Wear a dust mask during spreader loading and application in still conditions
- Shelf life is indefinite when kept dry and protected from contamination