Grain Storage Fumigation: How to Use Phosphine in On-Farm Silos

Getting phosphine right in on-farm silos comes down to three things: knowing when to fumigate, how to apply it and what products to use. This grain storage fumigation guide from FarmCo Moora covers each step, from a clean silo through to delivery, along with dosing rates, timelines and the safety essentials.

Grain Storage Fumigation: Key Points

• Only fumigate a silo that passes a pressure test.
• Grain must be 15°C or warmer for phosphine to work.
• Dose on the full silo volume: 3 tablets per 2 m³.
• Allow 10 to 17 days from tablets to delivery, longer without a fan.
• Phosphine kills insects present but gives no ongoing protection.
• Tell CBH staff about fumigated loads before tendering.

Eight Steps From Clean Silo to Delivery

1. Clean and test: Remove old grain, pressure test.
2. Cool the grain: Aerate to 20 to 25°C before sealing.
3. Monitor monthly: Sieve and trap at the silo top.
4. Apply tablets: If insects found or before outloading.
5. Expose: 7 to 10 days, fully sealed.
6. Vent: 1 day with a fan, 5 or more without.
7. Withhold: 2 days after venting ends.
8. Deliver: Tell CBH staff it was fumigated.

Why Seal the Silo for Fumigation?

The gas must stay high enough for the full exposure period to kill eggs, larvae, pupae and adults. In a leaky silo it escapes, the toughest insects survive and resistance builds.

Phosphine is a knockdown treatment, not a protectant. Hygiene, cooling and regular checks matter just as much.

Pressure Test Your Silo First

Test every silo before you fumigate. If a silo fails, do not fumigate it.

Minimum time for pressure to halve (AS 2628):

Silo type	Minimum half-life
New silos	5 min
Existing silos	3 min

When to Fumigate Stored Grain

Fumigate when monthly checks find live insects, or before grain is sold or delivered. Sample from the silo top, where insects breed first. Five adult beetles can mean around 450 insects across all life stages.

Sealing warm grain straight after harvest traps moisture and causes mould. Do not fumigate grain below 9% moisture.

Silo Fumigation Timeline

At 15 to 25°C with an aeration fan, plan for 13 to 17 days.

Stage	Days	When it ends
Exposure, fully sealed	10 days	Day 10
Venting	1 to 5 days	Day 11 to 15
Withholding	2 days	Day 13 to 17: deliver

Above 25°C exposure drops to 7 days. Without a fan, venting takes at least 5 days and can take much longer, so allow extra time.

Applying Phosphine Tablets

Each 3 g tablet of QuickPhos or Fumiken releases 1 g of phosphine. The label rate is 1.5 g per m³, which is 3 tablets for every 2 m³ of silo space.

Dose on the full silo volume, not the grain inside, so a half full silo still needs the full dose. A 100 m³ silo needs 150 tablets.

Seal all hatches, vents and fan housings first. Spread tablets in a single layer on non-flammable trays on the grain surface so the gas moves down through the grain. In silos over 150 t, recirculate the gas for the first 4 to 5 days.

Do not use when grain is below 15°C or silo humidity is below 25%.

Grain cannot be moved or delivered until venting and the 2 day withholding period are complete.

Phosphine Timing (QuickPhos and Fumiken labels)

Grain temperature	Exposure	Venting	Withholding	Total time
Above 25°C	7 days	1 to 5 days	2 days	10 to 14 days
15 to 25°C	10 days	1 to 5 days	2 days	13 to 17 days
Surface only, silo over 375 m³	20 days	1 to 5 days	2 days	23 to 27 days
Below 15°C	Do not fumigate. Phosphine will not work.

Venting: at least 1 day with an aeration fan, 2 to 5 days with natural draught (300 t or more), at least 5 days with no airflow.

Before Delivery to CBH

Any load with phosphine detected at CBH receival is rejected and cannot be tendered again.

Tell CBH staff the grain was fumigated and declare all chemical use on the Crop Declaration Form.

Some export markets need residue free grain, so check this season’s receival standards before using any protectant.

Grain Storage Products and Rates

Product	Rate	Notes
Phosphine tablets (QuickPhos, Fumiken)	3 tablets per 2 m³ of silo space (1.5 g phosphine per m³)	Sealed silos only. Surface only in silos over 375 m³ needs a 20 day exposure.
Dryacide (amorphous silica dust)	Empty storages: 2 g/m² as dust or 6 g/m² as slurry. Grain: 1 kg per tonne	Best on empty silos and equipment. No withholding period, but it can lower test weight, so ask CBH before treating grain.

Always read the label before use. Sumithion 1000EC (fenitrothion) is labelled for stored grain in WA by bulk handlers only, so it is not an on-farm option.

Safety: Phosphine Is Highly Toxic

• Wear a full face respirator with a P1 and phosphine gas filter. Check the SDS exposure standard.
• Never heap tablets or let them get wet.
• Do not re-enter until the full period is over or a gas meter reads clear.
• Sign silos with start and safe to open dates. Never fumigate alone.
• Deactivate spent tablets outdoors in soapy water or dilute acid until bubbling stops. Bury below 500 mm in an approved pit.
• If insects survive a fumigation, send them to DPIRD for resistance testing.

UPL QuickPhos® Dosing Guide

This section applies to UPL QuickPhos only. For other phosphine products, follow that product’s label.

Basic Principles of Treating Grain With QuickPhos

• Silos and sheds must be well sealed. If not, fumigation will not give adequate control and is contrary to label directions.
• Multiply tonnes of grain by 1.3 to give storage capacity, then use the table below to choose the product and amount.
• Work on a 20 day exposure period.
• Ventilation: forced air 12 to 24 hours. Natural or wind draught 2 to 5 days, depending on air velocity and structure size.
• Withholding period: 2 days after ventilation.
• Always read the label and follow all directions on the registered label on the container.

Note: UPL works on a 20 day exposure. Where this differs from the phosphine timing table above, follow the registered label.

QuickPhos Product and Amount by Storage Size

Storage capacity (m³)	Grain (tonnes)	Tablets (3 g)	Bags (34 g)	Bag chain (10 x 34 g)	Blankets (3.4 kg)
2	1.6	3
4	3.2	6
7.5	6	11	1
10	8	15
20	16	30	3
50	40	75	7	1
100	80	150	13	2
500	400	750	66	7
750	600	1,125	100	10	1
1,000	800	1,500	133	13
1,500	1,200	2,250	200	20	2
3,000	2,400	4,500	400	25	4

Blank cells mean no amount is listed for that product at that size. Source: UPL QuickPhos basic principles guide.

UPL QuickPhos Available at FarmCo

• Tablets 300 g flask: 100 tablets per flask. Use the complete contents in one application. Do not store unused tablets.
• Tablets 1.5 kg flask: 500 tablets per flask. Use the complete contents in one application. Do not store unused tablets.
• QuickPhos Bag Chain: 10 x 34 g bags per chain.
• Blankets 3.4 kg: 2 x 1.7 kg blankets.

QuickPhos® is a registered trademark of UPL Australia Pty Ltd · upl-ltd.com/au

Talk to Your FarmCo Agronomist

This is a general guide only. Always follow the product label and SDS. Label rates and CBH standards can change, so check before use. For advice on your storage, contact your FarmCo agronomist.

Sources: QuickPhos, Fumiken and Sumithion 1000EC labels · Dryacide · GRDC Groundcover · DPIRD (agric.wa.gov.au) · CBH (cbh.com.au) · UPL SiloKeeper app

Related Reading on the FarmCo Blog

(Suggested internal links — link to existing articles in the FarmCo How To and Resources section as they become available.)

• How to pressure test a grain silo
• Aeration cooling for stored grain
• Managing stored grain insects and phosphine resistance