What is a Trap Crop?

A trap crop is a plant that attracts agricultural pests, usually insects, away from nearby crops. This form of companion planting can save the main crop from decimation by pests without the potential issues and controversy involved in using pesticides. Trap crops can be planted around the circumference of the field to be protected, or interspersed among them, for example being planted every so many rows.
marigolds as a trap crop
Benefits of trap cropping

  • Better quality of main produce
  • Attract beneficial organisms
  • Enhances biodiversity
  • Reduce dependence on insecticides

How to use a trap crop.

There are two ways you can use trap cropping:

  1. One may use the same plant cultivar as a main crop and a trap crop. The trap crop is planted much earlier than the main crop in order to serve as food for the insects, and
  2. The main crop and trap crop are entirely different species.

Research has shown that hot cherry peppers trap crop can protect bell peppers by reducing damage from many insects, including pepper maggots. Early planted tomatoes can serve as trap crops for the multiple pests to protect a patch of desirable tomatoes.

Trap crops are, when used on an industrial scale, generally planted at a key time in the pest’s lifecycle, and then destroyed before that life cycle finishes and the pest might have transferred from the trap plants to the main crop.
example of trap crop
Examples of trap crops include:

  • Alfalfa planted in strips among cotton, to draw away lygus bugs, while castor beans surround the field, or tobacco is planted in strips among it, to protect from the budworm Heliothis.
  • Rose enthusiasts often plant Pelargonium geraniums among their rosebushes because japanese beetles are drawn to the geraniums, which are toxic to them.
  • Chervil is used by gardeners to protect vegetable plants from slugs.
  • Rye, sesbania, and sicklepod are used to protect soybeans from corn seeding maggots, stink bugs, and velvet green caterpillars, respectively.

How does a Trap Crop Work?

Recent studies on host-plant finding have shown that flying pests are far less successful if their host-plants are surrounded by any other plant, or even “decoy-plants” made of green plastic, cardboard or any other green material. The host-plant finding process occurs in three phases.

The first phase is stimulation by odors characteristic to the host-plant. This induces the insect to try and land on the plant it seeks. But insects avoid landing on brown (bare) soil. So if only the host-plant is present, the insects will quasi systematically find it by simply landing on the only green thing around. This is called an “appropriate landing”. When it does an “inappropriate landing”, it flies off to any other nearby patch of green. It eventually leaves the area if there are too many ‘inappropriate’ landings.

The second phase of host-plant finding is for the insect to make short flights from leaf to leaf to assess the plant’s overall suitability. The number of leaf-to-leaf flights varies according to the insect species and to the host-plant stimulus received from each leaf. But the insect must accumulate sufficient stimuli from the host-plant to lay eggs; so it must make a certain number of consecutive ‘appropriate’ landings. Hence if it makes an ‘inappropriate landing’, the assessment of that plant is negative and the insect must start the process anew.

Related  Using Beneficial Insects

Thus it was shown that Clover used as a ground cover had the same disruptive effect on eight pest species from four different insect orders. An experiment showed that 36% of cabbage root flies laid eggs beside cabbages growing in bare soil (which resulted in no crop), compared to only 7% beside cabbages growing in clover (which allowed a good crop). Also that simple decoys made of greencard disrupted appropriate landings just as well as did the live ground cover.

Decoy Trap Plants for the Home Garden

You can find many articles on the internet about trap cropping, specific trap crop info is scarce, particularly for the smaller home garden. The following list is compiled to give the home gardener ideas for using decoy plants, but is by no means complete. If you have a suggestion, please let us know so we can keep this community recourse as complete as possible.

Plant Attracts
Dill Tomato hornworms
Millet Squash bugs
Amaranth Cucumber beetle
Sorghum Corn earworms
Radishes Flea beetles, Harlequin bugs, and Cabbage maggots
Collards Cabbage worm
Nasturtiums Aphids
Sunflowers Stinkbugs
Okra Tomato aphids
Zinnias Japanese beetles
Mustard Harlequin bugs
Marigolds Root nematodes
Eggplant Colorado potato beetles

Nasturtiums as a trap crop for aphids
In addition to using decoy plants such as the above, other plants can be used to repel invading insects. Chives will repel aphids. Basil repels tomato hornworms. Tomatoes repel asparagus beetles. Marigolds are not only detrimental to nematodes; they repel cabbage moths, too.

Will using trap crops wholly eradicate your insect pest problem? Honestly? no completely, but if reducing the amount of pesticides you use in your garden or increasing yields without pesticides is your ideal, learning how to use trap crops may bring you a little closer to accomplishing this.

Trap cropping is one of the most valuable pest management techniques.

References:

  • Dr. Stefan Brueckmann. “Trap cropping”. Oisat.org. http://www.oisat.org/control_methods/cultural__practices/trap_cropping.html. Retrieved 2010-02-25.
  • Dr. Ayanava Majumdar (Dr. A) is Extension Entomologist and the State Coordinator for Sustainable Agriculture Research and Education, Auburn University
  • Horticulture Research International, Wellesbourne : “Insects can see clearly now the weeds have gone.” Finch, S. & Collier, R. H. (2003). Biologist, 50 (3), 132-135.
  • Alfredo Flores (March 8, 2010). “Geraniums Could Help Control Devastating Japanese Beetle”. United States Department of Agriculture Agricultural Research Service. http://www.ars.usda.gov/is/pr/2010/100308.htm.

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