Author: Brown Ink Admin

Caution: Research on unregistered pesticide use Any research with unregistered pesticides or of unregistered products reported in this document does not constitute a recommendation for that particular use by the authors or the authors’ organisations. All pesticide applications must accord with the currently registered label for that particular pesticide, crop, pest and region.

KEY POINTS

• To maintain pest-free stored grain in a condition required for feed,
  processing or seed, growers need to:
• make full use of good hygiene and aeration cooling;
• identify pest incursions earlier through monthly monitoring;
• select the correct storage treatments; and
• apply stored grain treatments correctly.

Managing grain storage

Generally, the combination of good hygiene plus well-managed aeration cooling, overcomes 85 per cent of storage pest problems. When fumigation is needed it must be done in pressure-tested sealable silos. For grain storage, three key factors provide significant gains for both insect pest control and grain quality.

Hygiene

The first grain harvested is often at the greatest risk of early infestation due to contamination. One on-farm test found over 1000 lesser grain borers in the first 40 litres of wheat that passed through the harvester. Therefore, cleaning-up grain residues in empty storage and grain handling equipment, including harvesters, field bins, augers and silos provides a safe start for the new season’s grain. Clean equipment by blowing or hosing out residues and dust, and then consider a structural treatment (See Table 1, page 2).

Aeration

Freshly harvested grain usually has a temperature around 30°C, which is an ideal breeding temperature for storage pests. Deal with high moisture grain promptly by aerating, blending or drying. Aeration fans fitted to stores can rapidly reduce grain temperatures. Studies have shown that rust-red flour beetles stop breeding at 20°C, lesser grain borer at 18°C and below 15°C all insects stop breeding. Aim for grain temperatures of less than 23°C in summer and less than 15°C in winter. Aerate grain as soon as it is placed into storage. For reliable results use an automatic controller to run fans.

Storage choices

When buying a new silo, purchasea quality, sealable silo fitted with aeration, and check with the manufacturer that it meets the Australian Standard for sealable silos. Experience has shown that at least two sealable, aerated silos on farm provide the option for effective fumigation and delivery program. Fumigation in unsealed or poorly sealed silos leads to the selection of resistant insects in stored grain. Many older silos were not designed to be sealed and cannot be used for fumigation, however fitting them with aeration can reduce insect multiplication through grain cooling.

Storage and treatment notes

Cereal grains

Buyers and bulk handlers are changing their acceptance of grain treated with insecticides. Before using a grain insecticide, always check with your potential grain buyers and bulk handlers (depot) for market acceptability. Identify storage pests before selecting a treatment. Always follow label instructions carefully.

Seed held on farm (cereals – wheat, barley, oats)

Seed that is dry, cool and sound (that is, not weather damaged) will remain viable for longer. In well managed storage, germination percentage should be above 95 per cent after six months. To achieve this, grain moisture content (mc) should be below 12 per cent. Grain temperature also has a major impact on germination. Aim for grain temperatures of 20°C and below in seed storage by using  aeration (with auto control). Wheat at 12 per cent mc stored at 30°C (too warm) hadless than 70 per cent germination after six months. Position small seed silos in the shade or paint them reflective white to assist in keeping grain cool. For insect control, treating seed with a grain protectant in combination with aeration cooling is recommended.

Pulse and Oilseeds

Insect control options are limited for stored pulses and oilseeds. Dichlorvos and grain protectants are not registered for use on these grains. Phosphine fumigation and controlled atmosphere may be an option. The effectiveness of phosphine fumigation on oilseeds is often reduced due to phosphine sorption during treatment. As limited chemical options are available, use good hygiene in combination with aeration cooling to reduce insect activity. Small seed-size grains like canola may need large-size aeration fans on stores. Always store these grains at their recommended grain moisture content level.

Fumigation

Read labels and only carry out fumigations in suitable gas-tight, pressure-tested grain stores. For effective phosphine fumigation, a minimum of 300 parts per million (ppm) gas concentration for seven days or 200ppm for 10 days is required. Gas will leak out very quickly from unsealed storages, resulting in poor insect control on all life-cycle stages (eggs, larvae, pupae and adults). Poor fumigations also increase the populations of resistant insects. As a general rule, only keep a silo sealed while conducting the fumigation (for example, one to two weeks). After fumigation has been completed, return to aeration cooling to hold the stored grain.

Table 1 Resistance and Efficacy Guide for Stored Grain Insects 2009 – Cereal Grains September 2009 (nort hern and southern grain production regions).

Phosphine resistance is widespread – plan, monitor, control for clean grain

• Dispose of grain residues and seed grading. Clean empty storage, grain handling equipment, including harvesters, field bins and augers.
• Stored grain should be sieved for the presence of insects at least monthly. Also check grain temperature and moisture.
• During winter storage, if grain temperature has been kept at less than 15°C by aeration live insect numbers are likely to be very low.
• Grain should be sampled three weeks prior to sale to allow time for any treatment.
• For effective fumigations, pressure test sealable silos at least once a year to identify any leaks and ensure they are maintained gastight.
• Take care when climbing silos to sample grain for insects and wear a safety harness. Sample from the base, and if safe, take a sample from the surface of the grain.
• Sieve a half litre sample onto a white tray. Hold tray out in sunlight to warm for 20 to 30 seconds to encourage insect movement.
• If live insects are found, identify them. Select the appropriate treatment for the grain type and insect. Check labels.
• Phosphine fumigation typically requires 7 to 10 days in a gas-tight sealed silo. When completed, open silo top with care, ventilate using aeration fan for 12 to 24 hours;
  the withholding period is then two additional days. If not aerated, open silo top and ventilate for five days.

FIGURE 1 PHOSPHINE RESISTANCE – THE NATIONAL SITUATION