Protecting Stored Grain From Insect Infestations

by Glenn Studebaker - IPM Coordinator, Row Crops - August 2, 2024

Corn harvest is around the corner and some growers plan on storing their grain on farm in bins. Stored grain pests can cause significant losses if left unchecked. There is a complex of insects that can infest grain stored in bins. There are several beetles as well as some caterpillars that will feed on grain during storage. Many of these species live for several months and some may live for up to 2 years. The maize weevil and rice weevil are considered to be the most destructive to stored grain. These species will attack and feed on unbroken kernels and can cause significant losses. Other beetle species such as the red flour beetle, confused flour beetle and sawtoothed grain beetle, prefer to feed on broken kernels and grain dust. All of these species have been detected in surveys of grain bins in Arkansas.  The first line of defense against these pests is placing grain into a clean bin. 

An important source of infestations in grain storage facilities is old grain and grain dust that has been left in or around the bin. Even a small amount of grain or dust can produce a large number of stored grain pests. Stored grain insects are very small and long lived. They can often survive for long periods of time with little moisture or food. Before placing fresh grain into a bin, floors should be swept clean of ALL old grain. Any spilled grain near the outside of the bin should also be removed. Areas that are often overlooked are augers and subfloor areas of the bin. These also need to be cleaned of old grain. Once all bins and equipment have been cleaned, bin floors and walls should be treated with a residual insecticide just prior to placing fresh grain in the bin. Malathion, Centynal or Suspend can be used to treat the inside of empty bins used for storing corn or grain sorghum.  Malathion is NOT LABELED for rice storage facilities and should not be applied to bins where rice will be stored. Also, liquid formulations of Malathion cannot be applied directly to grain, only dust formulations. Most importantly, many species, such as Indian meal moth, red flour beetle and lesser grain borer, have developed resistance to Malathion. Remember, proper sanitation of bins can go a long way in preventing insects from attacking grain while in storage. 

Once grain is ready to go into the bin, it should be treated with an insecticide if it is going to be in storage for an extended period of time. Always check labels before treating grain going into storage. While some insecticides can be used on multiple types of grain, others are restricted to only certain crops. An example is Actellic which can only be used on corn or grain sorghum, and as noted above Malathion cannot be applied in any form to rice grain going into storage. A list of insecticides for controlling insects in grain during storage can be found under the Row Crops section of Insecticide Recommendations for Arkansas - MP144 where a list of recommended insecticides and rates can be found. This information is also available in the Mobile Friendly Version of MP144. Application rates for bin wall and floor treatments can also be found in this section of MP144.  

Insecticide selection and/or rates depend on how long a grower plans on keeping the grain in storage. The figures below indicate the effectiveness of labeled products tested on stored corn grain. This study was funded through the Arkansas Corn and Grain Sorghum Promotion Board and gives us an indication on what products should be considered.  Figure 1 shows that Actellic, Malathion and the high rate of Centynal, protected stored corn for up to 2 years from natural occurring infestations of rice weevils. Figure 2 shows how Actellic at both the low and high labelled rates and Malathion provided protection for up to 431days in a laboratory study where grain was reinfested with rice weevils each month. 

Even under the best circumstances, infestations can occur if grain is stored for an extended period of time. Once grain becomes infested, fumigation will be necessary to eliminate insect pests. Fumigants are dangerous and extreme caution is recommended when using them. Never enter a bin that has been fumigated until it has been well ventilated. Fumigants also take 3 to 5 days to work effectively. 

This work is supported by the Crop Protection and Pest Management Program [grant no. 2021-70006-35512/project accession no. 1027188] from the USDA National Institute of Food and Agriculture, and from funding from the Arkansas Corn and Grain Sorghum Promotion Board.