Wednesday, October 13, 2010

Thwarting Corn Worms

Copyright Harvest McCampbell, 2007, published in the Hoopa People News

Fresh corn on the cob is one of the delights of summer. Whether you like it boiled or roasted, drizzled with butter or olive oil, sprinkled with salt and pepper or chili powder; I know your mouth is set for a taste right now. Nothing is more disappointing than pulling a plump ear off the grill, impatiently waiting for it to cool, shucking off the husk, and finding you have cooked yourself up a bunch of fat grubs.

As unappetizing as those bugs may be, they won’t hurt you one bit. I am not suggesting you actually eat them, although my grandmother used to suggest that to me. I would get lectures on how nutritious bugs were; and she would further ruin my apatite with stories of all sorts of bugs Native people used to eat. I was not convinced and I won’t try to convince you. Instead I will give you some pointers to reduce the infestation in your corn and a little advice on what to do if you find corn worms on the ears you planned to eat for dinner.

An ounce of prevention is always worth a pound of cure. If you’ve had worms in your corn before, it may not be too late to thwart them this year. Check your plants to see how the ears are coming along. If they are just beginning to put out silk, here is a simple and inexpensive trick that will greatly reduce the number of disgusting worms burrowing through your favorite summer treat. All you need is a little vegetable oil, a small jar, and an eye dropper or bulb syringe. Castor oil is supposed to be the best, because it is the thickest; but any vegetable oil will work just fine.

First take a close look at your developing ears. At the top you simply squirt a dropper full of the oil into the opening through which the silk is emerging. You want to wait until the silk is at least an inch and a half long. It is important not to get any oil on the tips of the silk, because that would interfere with pollination necessary to develop plump ears.

This little trick works two ways. First of all, the worms emerge from eggs laid by moths which crawl through that same opening where you just squirted the oil. Those that are fool-hardy enough to crawl through the oil usually don’t survive the experience. Moths breathe through pores in their abdomen. The oil can clog the pores and suffocate them. If they manage to survive suffocation, the oil also ruins their wings, making it impossible for them to fly to the next young ear and lay a few more eggs. Second of all, should a moth have beaten you to the ear, the oil will also suffocate the eggs and tiny young worms. For best control, you can repeat this trick every three to four days from the time the silk emerges until the corn is ready to pick. However, if you have lots of corn and little time, you might just want to invest in the castor oil and make the application a single time when the corn is most vulnerable; just after the silk has emerged.

There is a product advertised for single application treatments that contains oil mixed with Bacillus thuringiensis (Bt). Bt is marketed as a disease that only affects caterpillars, grubs, and a few other insects. It is incorporated into a number of products that are popular with many commercial organic growers and some organic gardeners. Bt gives the bugs a deadly case of the flue. Unfortunately it also kills native species and the bacteria can multiply and spread. If that weren’t bad enough news, recent research has shown that people can become infected with Bt. While fairly uncommon; there are well documented cases of folks with lesions in their eyes, lungs, and skin. (For more information search the Internet on “Bt / Human Infection.”) Bt infection is a greater concern for workers on organic farms, the elderly, the very young, or those with impaired immune systems; than it is for the rest of us. However, if my only choice was between those icky worms that never actually hurt anyone and bacteria that might, I would stick with the worms.

There is also a beneficial insect that can help control corn worms. According to research done by Cornell University some farmers have found that a tiny (non-stinging) wasp that goes by the unwieldy name, Trichogramma ostriniae, provides better control of corn worms than provided with commercial pesticides. These wasps parasitize the eggs and larva of a number of crop pests including cabbage worms, corn worms, and a number of borers that tunnel into the stems and fruits of our favorite crops. Home gardeners can easily attract these little guys to their gardens.

Adult Trichogramma feed on pollen and nectar from clover, golden rod, and carrot family plants. Queen Anne’s lace, fennel, and parsnips are a few carrot family plants very popular with Trichogramma wasps. To make sure your little wasps have plenty of fuel for their hunt, one plan is to plant the borders of the garden with nectar producing plants. Other options include inter-planting nectar plants in your rows or beds, or sowing the walk ways between the beds with white, rose, or red clover. These clovers can be mowed, they add nitrogen to your soil, and they may help keep weeds down. However, clover also attracts bees of the stinging kind. If you or the grandkids like to walk out in the garden barefoot, clover is best kept out of the walk ways and assigned to do its work in the border or in its own bed.

For those growing lots of corn for market, you might consider purchasing Trichogramma for release in your fields. The best crop protection with the least monetary expenditure is supposed to come from releasing 30,000 Trichogramma wasps per acre when the corn is in the 4-6 leaf stage. Unless you are growing late corn, you will probably have to wait until next year to make this experiment. That will give you time to establish some nectar bearing plants to help your Trichogrammas thrive. These little insects are cold hardy, so once you get them established they just might keep working for you for many years. If you are interested you can find more information here:

Trichogramma ostriniae and other Trichogramma species may be available through your favorite organic gardening supplier or catalog. If not, IPM Labs grows out Trichogramma and other beneficials by special order. You will need to contact them well in advance. They can be reached by e-mail or phone: / 315-497-2063.

Meanwhile, if you do find a few bugs, just remove the infested and fouled part of the ear by breaking or cutting it away. Rinse the remainder well, and boil; or wrap in the rinsed husks and some foil and pop them on the grill. While this little task may not be for the squeamish, if you get it accomplished well before your meal it won’t gross out your guests. That’s a mistake I recently made, and I definitely learned my lesson.

That’s all for now folks, but stay tuned. Next week we will be talking about the very flavorful Greek oregano. Meanwhile, you can find probably find me out in the garden, Digging the Dirt.


Personal experience and Cornell University research on beneficial wasps, some of it located here:

P.S. I know this post isn't timely for Northern Hemisphere readers--but I am sharing it here as part of a conversation on facebook about controlling caterpillars. Please feel free to add me on facebook and join in the conversations . . .

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