|University of Kentucky Entomology|
CONTROLLING INSECTS IN STORED GRAIN
By D.W. Johnson and L.H. Townsend, Extension Entomologists
|Table 1.--Bushels of Grain in a 4-inch Grain Layer in Bins of Various Sizes|
|Bin Diameter(ft)||Surface Area(ft 2)||Bushels(in a 4-inch layer)||Proportion of 1000 bu|
|Based on 1.25 cu ft/bu.|
Infestation in the Grain Bulk
Fumigants are gases that penetrate the grain and kill insects both on and in the grain. They are very toxic to man and animals and should be applied only by trained, experienced operators working in pairs.
Once an insect infestation has become established, there are only two treatment options: (1) move the grain and apply a protectant during transfer or (2) fumigation. Both choices have good and bad points. Application of grain protectants during movement will provide some residual protection. But moving grain is costly, time consuming and requires additional bin space. Also, if good control is not achieved, movement will spread the insects throughout the grain mass. On the other hand, fumigation works very well and is relatively cheap. Fumigants are gases that penetrate the grain and kill insects both on and in the grain. They are very toxic to man and animals and should be applied only by trained, experienced operators working in pairs. But because it is very sensitive to poor technique, many failures occur. Also, it is dangerous and provides no residual protection.
Several factors are important in assuring successful fumigation.
Causes of Fumigation Failures
Fumigation failures can usually be attributed to one or more of the following:
Should fumigation become necessary, a variety of compounds are available for treatment (See Insecticides and Fumigants). Fumigants are inherently dangerous and should be applied only by trained operators. Operators should wear a full face gas mask equipped with the proper canister, and have access to self contained breathing apparatus, and another person should always be present during fumigation.
Grain bin inspection provides important information on the general condition, temperature, moisture and pest activity of stored grain. Inspections allow early detection of problems and enable corrective action to be taken before damage becomes severe See: "Aeration, Inspection and Sampling of Grain in Storage Bins," Extension publication AEN-45, provides procedures for checking storage facilities.
Using Probe Traps for Insect
|The commercially available "probe" traps may be the easiest and safest way to monitor for several beetles that can infest bins. These traps are hollow "plastic" tubes with a series of downward sloping holes all along the sides. The top is a flat cap. The bottom is a pointed piece that screws in place. Insects crawling into the tube through the small holes can accumulate at the pointed end of the trap. A nylon line should be securely attached for easy retrieval from the grain mass.|
These traps can be inserted in the grain using a long pole with a cup device on the end. This device is easily made using a paint roller extension handle and some "PVC"plumbing fixtures. Attach to the extension handle, a PVC "reducer" that has one side just about the size of the screw on the end of the extension handle while the other side is large enough to serve as a cup over the end of the trap. This will allow you to push the trap into the grain from an inspection hatch, internal ladder, or some other safe place, thus avoiding having to cross the grain surface.
The trap is retrieved using a nylon line which was attached to the trap before it was placed in the grain, and tied off to some convenient location in the bin. The line will also serve to keep traps from being sucked into the grain stream in case they are forgotten at unloading time.
How many traps are needed? The greater the number of trap samples, the greater the probability of detecting insect activity. For grain, the standard is 4 to 5, certainly now fewer than three, per round bin.
Thresholds for a one-week sampling period vary with species sampled and the grain Temperature (Table 2). If grain temperature is below 60o F, the numbers in Table 2. indicate a very high population size.
|Table 2. Insects per trap week above which discounts occur. (Oklahoma State University)|
|Species||Threshold levels per week|
|Rusty grain beetle||3,000 - 5,000|
|Lesser grain borer||5|
|Red flour beetles||1,000|
Economics of Pest Control
The constant fluctuation of grain prices and costs of insecticides, as well as attitudes of local buyers, make it impossible to set a specific cost-return value for treatment of stored grain. In Kentucky, most often the cost of an insect infestation in stored grain is that the buyer pays less for that grain. Find out what local buyers dock for infested grain, and compute the cost of treatment to see which provides the best return. If grain is plentiful, buyers can be choosy so the dock for infested grain will be greater. In that case, treating infested grain is usually more cost effective. On the other hand, if grain is scarce, buyers may not dock at all for insects, so treatment would be cost prohibitive. It is never cost effective to treat non-infested grain.
Insecticides and Fumigants
Labeling and application regulations for fumigants and grain protectants are subject to change. To insure that information on these products is as current as possible lists of insecticides and fumigants for use in stored grain may be found in the appropriate annually revised commodity publications as follows:
ENT-13 Insecticide Recommendations for Soybean
ENT-16 Insecticide Recommendations for Field Corn
ENT-24 Insecticide Recommendations for Grain Sorghum (Milo)
ENT-47 Insecticide Recommendations for Small Grains (Barley, Oats, Wheat)
You may view these publications on line at: www.uky.edu/Agriculture/PAT/recs/rechome.htm
Do not use malathion as residual treatment for empty bins, a protectant or ‘capout' treatment. Malathion labeling is being removed for stored grain. More importantly, several stored grain pests have exhibited tolerance to malathion.
Common Stored Grain Insects In Kentucky
A variety of insects can be found in Kentucky stored grain. Fortunately, only a few are responsible for most problems and most of them are relatively easy to identify. These pests are divided into two main groups the beetles and the caterpillars. The caterpillars are easily identified. However, stored grain beetle pests are quite small so a hand lens is needed to see enough features to determine if important pests are present.
|Indian meal moth is one of the most common and troublesome insects attacking most any type of stored grain. The adult is a moth with a coppery color on the outer two-thirds of the front wings. Presence of the adult, though not damaging, can indicate the presence of an infestation. The moths lay eggs on the gain surface. These eggs hatch into the caterpillars (worms) that cause damage. The worm is about ˝" long when grown and whitish in color. IMM rarely causes extensive kernel damage, or grain discount at the time of sale. However, the larvae may completely web over the grain surface, thus preventing proper air movement for aeration and fumigation and causing surface grain moisture accumulation and "top crusting".|
|The most common beetles, often called "bran bugs", do not feed on whole sound kernels, but rather live on broken kernels, dust, and trash. There are two major types in Kentucky the "flour beetles" and the Cryptolestes beetles. These insects are likely to be found in every bin of stored grain in the state. The real question is are there enough to do and damage?|
|There are two flour beetles, Red flour beetle and the Confused flour beetle. They look very much alike and are separated by examination of the last three segments on the antennae. However, these beetles are usually found together in an infestation and do about the same damage.|
There are also two common Cryptolestes beetles. They are the flat grain beetle and the rusty grain beetle. They look very much alike and are about one-half the size of the flour beetles. They are very flat in appearance and have beaded antennae about one-half as long as the body. They are often found in mixed infestations with flour beetles and do a similar type damage, but it takes two to three times as many flat/rusty grain beetles to do the same amount of damage as the flour beetles.
|Perhaps the two most dangerous insects in Kentucky stored grain are the "weevils", which are usually found in corn, and the lesser grain borer which is more often a problem in wheat.
The weevils are relatively easy to tell apart from other insects because of their "snout". These are long, thin, downward curving mouth parts sticking out from the head.
The lesser grain borer also has a distinctive shape. However, it is the overall look of this insect that allows the identification. Lesser grain borer are very cylindrical in shape and both the head and tail end look very flat. It is kind of like using a straw to take a plug out of an apple only much smaller.
Both the weevils and lesser grain borer are primary feeders. They both feed on whole, sound kernels and their young develop inside the kernel. Infestations of these insects are very important.
Most other insect pests are secondary feeders. They cannot feed on whole sound kernels, but rather do their damage by their presence, and the heat and moisture they generate.
There are a large number of other insects that can infest stored grain. You may find information, pictures of these insects and links to other storage sites at: IPM in Kentucky Farm Stored Grain
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!