Prevent pests and rodents in stored maize

July 2025

GRAIN THAT IS STORED IN BULK OR EVEN FOR FAMILY USE AT HOME, CAN ATTRACT INSECTS, PESTS AND OFTEN ALSO FUNGAL INFECTIONS. THIS CAN HAVE A DEVASTATING IMPACT ON THE GRAIN’S QUALITY AND VOLUME. TO STORE MAIZE SAFELY, ENSURE THAT PROPER DRYING TAKES PLACE, USING APPROPRIATE CONTAINERS AND CONTROLLING THE TEMPERATURE.

Did you know that one of the most serious yield losses in developing countries is due to post-harvest losses? Although maize can be stored for a considerable period in an unprocessed form without deteriorating, it should be stored in well-ventilated, dry areas to protect it against pests, rodents and moisture.

Mould occurs if the grain was not dry enough at harvesting, or if it is exposed to high humidity or moisture due to poor storage management. Fungal infections will cause rot and the development of aflatoxins. These mycotoxins are poisonous to livestock and can even cause serious health issues for humans. Mycotoxins are a real threat to consumers of maize products and livestock, but with the correct safety measures and efficient storage in place, it’s a threat that can be managed.

GUIDELINES FOR GOOD STORAGE CONDITIONS

1. Thoroughly clean storage facilities, removing old grain, dirt and dust that could hide insects.
2. Ensure that proper storage is used. Repair any structural cracks or gaps to prevent moisture build-up and insects from creeping in.
3. Check for insects in aeration ducts and under perforated floors. 
4. Use appropriate containers such as ventilated bins, silos or airtight bags to protect the product against moisture, pests and rodents. Hermetic bags are particularly effective for long-term storage, as they prevent oxygen and moisture from getting to the grain. 
5. Ensure the storage facility is dry, well-ventilated and has a solid floor. 
6. Store maize at less than 14% moisture content to inhibit insect reproduction.
7. Do not mix new maize with older, potentially infested grain. 
8. Avoid stacking maize too high, as this can damage the bottom layers. If possible, keep bags off the ground and away from walls to prevent insect access. 
9. Use insect probe traps, which can be inserted in the loose grain layer at the top. Insects entering the probe are captured at the trap’s bottom.
10. Periodically check the maize for any signs of deterioration and adjust storage conditions as needed.

STEPS TO CONTROL PESTS
A comprehensive strategy is needed to control insects in stored maize effectively as 25% of all stored grain worldwide, is lost annually to damage caused by insects. This makes fumigation a necessity.

For smaller farmers, Jerry Mthombothi, regional development manager at PGP’s Mbombela Office, says phostoxin tablets (which contains aluminum phosphide) can be used to prevent weevil infestation. This product can also be used to control rodents. Please remember to wear protective clothing when using any pesticides. Regularly inspect the stored maize for insects and rodents, and take steps to control any infestations.  

According to Gerhard Verdoorn, operations and stewardship manager at CropLife, controlling stored grain pests is a specialised field of pest control. ‘The greater the volume, the more specialised the treatment becomes. For a small-scale farmer, storing a few bags of grain for own use, it is possible to treat the bags with a deltamethrin/piperonyl butoxide spray to fend off undesired insect pests.’ Just remember not to spray directly on to the product. In silos – which may house as much as 8 000 tons of grain – spray treatment is not a feasible option and fumigation is about the only viable treatment protocol to remove stored grain pests.

Implementing these strategies can significantly reduce the risk of insect infestation in your stored maize. Regular inspection of the maize and storage area is also essential.

REFERENCES
https://www.fao.org/4/t1838e/T1838E04.htm#Who%20stores%20and%20why
https://www.roff.co.za/blogs/blog/an-introduction-to-insect-infestation?_pos=1&_sid=6978b2f02&_ss=r 
https://www.roff.co.za/blogs/blog/effective-grain-storage-to-manage-maize-supp 

Publication: July 2025

Section: Pula/Imvula

Author: COMPILED BY THE PULA EDITORIAL TEAM