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Frequently Asked Questions: Detecting Insects in Stored Grain
October 2006 Why is monitoring stored
grain essential? Why is monitoring stored grain essential? Checking for problems in stored grain is equally as important as scouting for problems in the field. Monitoring for insects or mould requires diligence, proper tools, and information. Regular inspection of the grain bin will help you to determine whether or not a problem exists. What control options are available? Whether you choose to
use cultural (non-chemical) methods or chemical methods, a choice has to
be made if you discover potential problems. Choosing combinations
of cultural and chemical methods constitutes what is known as integrated
pest management, or IPM. Careful consideration and application is required
when employing any of these choices.
How do I evaluate the treatment? After completing treatment of stored grain, it is important to follow-up with periodic grain checks to evaluate how well the treatment worked. Additional or alternate treatments may be required if the first attempt did not provide adequate control. Environmental factors may influence the effectiveness of certain treatments, making them less effective. To give your plan a “tune up,” follow-up with additional monitoring in order to evaluate the effectiveness of the method you chose. Why is the balance between temperature and moisture important? Because insects are cold
blooded organisms, they require warm external conditions in order to be
active. At approximately 10° C, insect activity tends to
stop. Therefore, cooling the grain to this level is strongly recommended. Ultimately,
cooling the grain in the fall to where it is within 5° C of the outside air
temperature will provide the best management to prevent moisture migration
within the grain mass. If moisture movement is stopped, there will be less
opportunity for significant condensation to accumulate in concentrated areas
within the grain mass. In the spring, the grain should be slowly warmed,
bringing it close to average daytime temperatures.
What are the time guidelines for sampling stored grain? When grain is first placed
into storage bins, it will probably require more vigilant monitoring. Twice weekly or more frequent examinations may be necessary. Once
the grain has stabilized, the grain can be monitored once a month, if the
temperature of the grain mass remains above 10° C. When the grain mass is
cooled to less than 10° C, monitoring efforts can be reduced significantly. Remember,
small problems are indicators that potential larger problems may be just
ahead. Watch for signs such as: unnatural musty odours; visible vapour mists;
significant differences in temperature within the grain mass; and snow melting
off the bin roof faster than other unheated bins. Keep in mind that the
longer the grain is in storage, there is a greater chance for infestations
to develop.
What tools can be used for sampling stored grains? Grain probe traps are commonly used to detect the presence of insects in stored grains. The traps are inserted into the grain mass and left for a period of time. This allows insects to crawl into the probe for counting and identification at a later time. Populations of insects should be monitored periodically to see whether there is any increase or not. These traps are good for monitoring beetle-like insects. Consistent trapping intervals are important in providing accurate counts, and in determining whether or not population increases are occurring.
Grain triers and bullet probes are also useful for monitoring stored grains for insects. However, they are only useful when the sampler is present. Trier samples should be taken from the top centre area of the grain mass. South to southwest quadrants of the bin, where temperature increases are more likely, are areas where insect activity might also be increased. Check areas where moisture might have contaminated the grain, especially around doors and aeration fans. Deeper regions of the grain mass should be checked using bullet probes. Use a #10 (2.0 mm aperture) sieve to check for insects in cereal grains. Samples taken from the surface of the grain mass must be warmed before screening to stimulate insect movement. A #20 (0.85 mm aperture) sieve is required for oilseeds. A simple way to check for heating is to insert a metal rod into the bulk of the grain for one hour, making note of an increase in temperature. This will indicate whether heating is occurring or not.
Pelican samplers and similar devices are used to gather samples of grain while it is flowing. The composition of samples is used to determine presence and quantity of insects in the grain. To detect insects in samples of grain, warm the collected grain in a screened funnel. As they move away from the drying grain and high heat, they fall into a collecting flask where they can be identified and counted (see figure to the right).
The following checklist may be useful to narrow the focus on what to look for when monitoring stored grains.
How is temperature used as a monitor? Installation of permanent or temporary temperature sensors is useful for monitoring grain condition, the potential for insect infestation and, ultimately, spoilage. These systems often consist of cables hanging down through the centre of the grain mass with battery operated monitors. The system can record temperatures at various depths throughout the grain mass, and show variations as well as monitor cooling fronts resulting from aeration. When grain spoils due to mould or insect growth, heat, water and carbon dioxide are produced. The heat causes the spoiled grain temperature to rise. High temperatures do not necessarily mean spoilage is occurring. Sometimes, grain placed into storage at the proper moisture content may have been harvested at fairly warm temperatures. Nearby insects may infest such grain and be quite active. Therefore, it is imperative that these grains be cooled by aeration, or by turning as soon as possible.
How do I measure carbon dioxide to detect insects or moulds?
Excess carbon dioxide is a product of deteriorating stored grain. Increased levels of CO˛ indicate that insects, mould, or excessive respiration are present. Because the gas permeates through the entire grain mass, it can be measured from outside the isolated problem zone. An apparatus such as the one illustrated below is useful for monitoring CO˛ levels indicating the condition of stored grain.
Information Sources Agriculture and Agri-Food Canada, Cereal Research Centre, Protection of Farm-Stored Grains, Oilseeds and Pulses from Insects, Mites and Moulds Agriculture and Agri-Food Canada, Cereal Research Centre, A Slide Show on the Pests of Stored Grain and Food Products Colorado State University, Cooperative Extension, Managing Stored Grain University of Minnesota Extension Service, OSU - Stored Product Management - Pub.E-912 :Wheat and Barley Storage Kansas State University, Management of Stored Grain Insects - Part I, Management of Stored Grain Insects - Part II, Management of Stored Grain Insects - Part III Acknowledgements Dale Risula, P. Ag., Integrated
Cropping Management Systems Specialist, SAF For more information, contact: E-mail: aginfo@agr.gov.sk.ca | ||||||
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