Consider stored grain pest management strategies
before and after storage.
By Phillip G. Koehler
Stored grain of almost any kind is subject to attack by insects. The insects that attack stored grain are highly specialized to exploit the stores man has set aside for himself. Stored products insects are, in most cases, insects of small size with a high reproductive potential. Therefore, they are easily concealed in grain and grain shipments and have been carried to all parts of the world. Once established in a commodity, these pests are usually difficult to control.
In general, stored products pests thrive in warm, humid environments. Grain with high moisture stored in warm conditions is usually most susceptible to insect infestations. Stored grain pests are important since they contaminate food, lower its nutritive value and create conditions favorable for mold growth.
Pests which attack whole grain usually develop and feed inside the kernels of grain. They can be easily overlooked in grain shipments since they cannot be seen. These pests are not usually capable of existence outside the grain kernel as immature insects. Examples of whole grain pests are the rice weevil, the granary weevil, the lesser grain borer and the angoumois grain moth.
Other insects that attack grain are usually unable to penetrate whole grain. These insect pests however, can attack grain after it has been either mechanically broken or attacked by whole grain insects. Examples of these secondary pests are the confused and red flour beetles, Indian meal moth, Mediterranean flour moth and the sawtoothed grain beetle.
Grain may become infested in a number of ways. One of the most common means of infestation starts in the field. In Florida, it is not uncommon for freshly harvested corn to have a 10 percent infestation rate. Another common means of infestation is storing grain in or near infested storage facilities.
Monitoring For Stored Grain Pests
Pheromone-baited traps are a good tool to monitor for the presence or absence of stored grain pests. These traps can be used to assist in stored grain management by:
1. Inspecting hidden infestations deep in bulk storage or bagged commodities
2. Identification of pests
3. Delineating the extent of a problem
4. Determining the effectiveness of control methods
Traps can be placed either indoors or outdoors. Outdoor trapping around the perimeter of the storage facility can either intercept insects migrating indoors and lure them away from the stored product or help predict future infestations. Wild populations of most stored product pests are common in Florida. These outdoor placements can prevent infestations by capturing insects as they migrate into the commodity. Or these outdoor placements can help predict the arrival of insects that would reproduce in the grain.
Indoor trapping can be used to determine the presence or absence of insect infestations. Trapping can also be used to determine the location of infestations. By placing the traps in a grid, the location of infestation can be determined and infested products either isolated or removed. The trap catches can also be used to determine the need for treatment.
Reduce Insect Populations Before Storing
Grow resistant varieties if available. Some varieties of corn have characteristics such as long, tight husks that will help to keep down weevil and other insect damage.
Store grain only in bins that have been cleaned thoroughly of waste materials such as old grain, trash or feed sacks that may furnish living quarters for insects. Sweep down ceiling, walls, rafters, beams and other areas where old grain and dust can lodge. Clean up old grain around and beneath the bins. Burn or bury all refuse collected during the clean-up.
Empty bin sprays are used to kill insects before grain is placed in storage. Apply products to all surfaces of the bin after thorough cleaning. Make sure the product used is labeled for stored grain facility. Many products are not labeled for direct grain treatment, but can be applied to empty bins.
Grain Protectants & Surface Treatments
The grain being stored should not already be heavily infested, and the moisture content is not above 12 percent. (High moisture grain attracts insects and enhances more rapid breeding than does dry grain.) Grain that will be stored for several months should be treated with a grain protectant as it is being placed in storage. Products registered as grain protectants are sprayed or mixed with the grain as it is being loaded. They should only be used on clean, dry grain.
Grain treated with protectants should be inspected at monthly intervals to guard against the possibility of infestation. These inspections should not be limited to the surface of the grain, but should extend down into the grain. If treated grain becomes infested, it can be fumigated.
Grain surface treatments help protect grain from infestations starting on the grain surface. They should be applied to the grain surface as soon as the bin is filled. They may need to be reapplied anytime the grain surface is disturbed.
Grain can become infested with insects even though everything has been done to prevent infestation. If the infestation is mainly associated with the surface of the product, a surface treatment can be applied. But, if the entire mass of product is infested, fumigation is the best method of control. Fumigation is the process of releasing a gas to control insects. Fumigation is good for control of food pests because once the product is aerated, the gas dissipates and does not leave behind harmful residues.
For fumigation to be effective, the gas must be confined to the commodity. This approach is usually accomplished with tarps or plastic sheeting. Fumigants are highly toxic and are restricted use items requiring pesticide certification as a private or commercial applicator.
Follow all precautions given on the label of the insecticide you use. All fumigants mentioned give off poisonous vapors. They have an anesthetic action, and a worker may be suddenly overcome without noticing adverse symptoms.
Therefore, never fumigate grain without the assistance of another person, and never stay inside the bin unless you are protected by a gas mask approved for the type of fumigant you are using.
Dr. Phillip “Phil” G. Koehler is a professor of entomology and nematology at the University of Florida in Gainesville.