CORN - KING
OF THE INSECTARY REFUGE PLANTS
Corn or maize, Zea mays L., sparsely interplanted in hills, using a mix of corn seed with differing maturity periods (e.g. early to 120 days and longer development times) will help attract and nurture sets of predatory and parasitic insects beneficial to biological control of many different market crops. These hills of corn act like pheromone or black light traps that attract and grow pests of corn. Where hills are sparsely distributed, one or two per acre, they provide plant food for primary consumers of corn and habitat to grow the general predators and parasites known to be useful in many market crops.
Mixing corn with other grasses--sorghum, sudan or cereals--will create even more diversity of food and habitat. Farms with heavy pest pressure may benefit from an upwind hedgerow that could include a corn-sorghum mixture in addition to the interplanted hills. The first couple of years of transition from chemical to biological farming is an especially important time to use border and strip refugia. Some sorghum varieties grow to 14 feet adding extra mass and height to present physical barriers against wind, insects and cross-pollination. Varying heights of plants enhances the architecture for orb-weaving spiders.
Corn (and sorghum) will grow minute pirate bugs, several species of ladybugs, many diverse parasites that attack armyworms and cutworms, corn rootworms and leafhoppers. Many species of Tachinid fly parasites and a dozen or more parasitic wasps that attack corn earworms and rootworms and other common pests are found in corn (unless it has been treated with pesticides). Some predatory mites survive well on pollen in these refuges until their favorite meal of spider mites and/or thrips move in. A few hills will enhance beneficial insects and guarantee their timely presence when migrations of pests begin. The hill functions as a "hot spot" of pests that will grow the key biological control insects naturally. As the beneficials consume their prey in the corn, they move into the market crop looking for more insects and mites. Additional inundative releases of beneficials into the market crop, timed for pest invasions into the market crop, are made more effective by the greater diversity of biological control organisms.
Corn is a hardy, easy to grow annual providing a sequence of pollen producing tassels offering a steady flow of insect food, pollen, corn silk, corn ears and seed that act like a pheromone beacon. Corn pollen provides food for flower thrips that is an ideal food for minute pirate bugs: corn earworms. army worms, stalk borers, for lacewings and lady bugs and diverse sets of parasites: of beetles like the corn root worms and flea beetles: moth egg hosts for Trichogramma spp.; continuous new growth for several species of corn aphids and their parasites, and others. There are other plants such as sunflowers/collards and various legumes, alfalfa, that are often used in refuges, but they are not as easy to use as corn.
Many of these corn pests prefer the corn refuge plantings to any of the alternative host crops, such as cotton, tomatoes, and beans. Orchard crops benefit as well. Walnuts almonds, pecans and most stone fruits that are conventionally grown in monoculture are not attractive to many biological controls. The corn refuge is an economical way to guarantee the presence of beneficial insect work animals, ready to suppress sudden invasions of aphids, mites, moth and butterfly larvae and pupae and possibly root infesting beetle larvae and other soil pests, such as walnut husk fly, flea beetles and Diabrotica beetles
Corn plants that are relatively free of pests attract green lacewing adults to feed. Many beneficials feed on the water of gutation (nutrient-laced droplets of plant water that bleeds from the leaves) even when no insect honey-dew is present. Trichogramma adults have been observed to survive extremely high temperature by hanging out near transpiring stigmata. Wasps, like Trichogramma, can live up to four times longer when there is a carbohydrate food source in the field. Tiny wasps like Trichogramma can be found running along the corn silks looking for corn earworm eggs to parasitize so the next generation of wasps will be present to attack eggs of moths invading the market crop.
Corn should be planted in small amounts in succession plantings. Maintaining a sequence of small plantings is more important than fewer plantings of more plants. When corn matures and no new plants are shedding pollen, the corn pests will no longer stay in old corn and may enter the market crop. Corn starts pollinating in about 20 days from planting and there is about a three week window of shedding pollen. Some, like Black Aztec, are more variable in ripening. A long (100 day) season may shed pollen longer and should stay attractive for insects well into September. Planting sequences of corn refuges through to harvest of the market crop will protect against this possibility. Planting successions of both early and late varieties further assures a continuous food supply for beneficials.
The amount of land required is minimal, because the insectary plantings are located outside or at the edge where there is a need for protection of the outside rows of crop from dust and infrared radiation. A diverse, well-planned perennial hedgerow may be possible along drive roads leaving space for sparsely planted hills of corn and sorghum in between or in front of the perennials. A more diverse flowering annual insectary mix can be added in corners and single rows along roads or in the roads where they help compete with weeds. No extra land is needed for interplantings of hills of corn in skips that appear in the market crop during the season.
The focus of the habitat enhancement is on the entire natural enemy complex system through adding plant biodiversity in a cost-effective way. The great thing about this new paradigm of habitat diversity is its flexibility. Each farmer can decide the best plan for his or her cropping system. A variety of resources are available from Fish and Wildlife and the Resource Conservation Districts to provide the latest knowledge to help you design the best habitat building program and turn your pest management budget into a beneficial insect management budget.
Copyright 1998 The Dietrick Institute