Manage Indianmeal Moth

Throughout the growing season, you’ve done everything to protect your crops from pests. It’s only natural that you may want to breathe a sigh of relief now that your grain is harvested and safely stored. But, just because it’s behind corrugated steel walls doesn’t mean industrious insects can’t find it. And, perhaps one of the most pervasive and persistent foes is the Indianmeal moth (IMM).

IDENTIFY THE PROBLEM. You’ll first notice a problem in your bin when adult moths start fluttering above your grain. By the time you see these tiny pests, they’ve been there awhile. The IMM is ½-inch long with the upper two-thirds of the wing covered in cream-colored scales. A dark band separates this section from the reddish-brown scales covering the remaining third of the wing. If these scales are rubbed off, the moths may instead have a tawny to dusty-gray appearance.

The IMM lay tiny eggs loosely on its food source, making the eggs hard to find. The larvae, however, are easier to locate. They’re off-white (sometimes pink or green-hued) with a darker-colored head. IMM larvae are mobile and move about the grain as they feed. They leave behind trails of silk, which accumulate and cause the grain to clump together and harden. These clumps are often the first signs of a problem. The larvae are ½ inch long at maturity and leave their food source when the time comes to pupate. The pupae are brown, ¼ inch long and wrapped in silk. IMM can often be found on the walls or other surfaces of the food source’s container, usually in tight spaces.

DAMAGE. Larval feeding consumes food meant for humans or animals, but the primary damage IMM cause is through food-quality loss. IMM larvae leave silk, fecal pellets and molted skins in infested food sources, making it unfit for consumption. The silk from a bad infestation is strong enough to create large, hardened masses of grain. These masses can damage equipment and are safety hazards to workers operating inside grain bins, as they may collapse below or fall on top of personnel. If you must enter a bin, be sure to wear the proper safety equipment.

MANAGEMENT. Prevention is the best tactic for controlling IMM. Clean bins of old grain and apply an insecticide treatment like Tempo 20 WP or Tempo SC Ultra on the inner and outer walls before loading grain. A grain protectant such as Diacon-D IGR (S-methoprene) or Actellic 5E (pirimiphos-methyl) can prevent IMM penetration into the grain when applied while loading. Protectants are grain-specific, so make sure that you choose the right one.

Seal the bin and keep grain cool (less than 60ºF), and dry to minimize the risk of an infestation. Hang pheromone traps in the headspace of the bin no more than 10 feet from the surface to monitor for moths. Check the traps frequently, and replace lures and traps regularly.

If an infestation occurs, the most effective approach is to dispose of the contaminated grain and clean the bin. If that’s not possible, fumigating the grain is your best option. Products like Phostoxin (phosphine gas) can be used in grain bins. Other gases, such as ozone, are also available. However, fumigants don’t provide residual protection. Be sure to keep the bins sealed once the gas is gone. Fumigations should only be applied by trained and licensed professionals.

For More Information:

> Purdue University Extension IMM Resources:

> Purdue University Extension Stored Grain Insect Pest Management

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