Trap Cropping

Every year, there are garden favorites that we plant religiously. Just as consistently, the same pests come, causing damage and carrying disease. What if there was a way to lure those pests away from your garden faves?

There is. It’s called trap cropping.

Mature mustard plants lure flea beetles away from young broccoli plants (USU Extension) CC BY 3.0

Trap cropping refers to the purposeful planting of crops known to attract or repel specific pests within and around the crops you are trying to protect. This distraction reduces the damage done by pests. In some cases, the attractant trap crop can interfere with the pest’s lifecycle, or kill it outright. In other cases, as pests start feeding on the trap crop, you harvest it, breaking the lifecycle of specific pests.

Trap cropping is a form of companion planting (better known as intercropping). While mint, garlic, nasturtium, and fennel have often been touted as cure-alls for many pest problems, the science behind trap cropping is still relatively new and I was unable to find enough research geared specifically toward those plants. 

Fear not, however, as there is plenty of good information you can use to protect your garden plants!

How trap cropping works

Trap crops distract pests away from food crops. By providing a rich food source for these pests, they are less likely to damage your food crops. Also, heavy pest infestations attract beneficial predators, such as lacewings and lady beetles. Once an infestation occurs, the trap crop can be fed to your chickens, tilled under, or composted. In commercial fields, pests attracted to trap crops are killed off with pesticides or vacuumed off the plants and destroyed.

Types of trap cropping

There are several types of trap cropping:

1. Conventional trap cropping places an attractive low value crop next to a high value crop. Examples of conventional trap cropping are planting collards near cabbages to provide protection from the diamondback moth, installing frequently mowed alfalfa near cotton plants to protect against lygus bugs, and planting mustard between rows of broccoli to lure flea beetles away.
2. Perimeter trap cropping occurs when an attractant plant is grown around the perimeter of a cash crop, surrounding it completely. This barrier interrupts pests before they ever reach the high value crop. One popular perimeter trap crop is the use of hot cherry peppers planted around bell peppers. Apparently, the hot peppers stop pepper maggots from infesting the sweet peppers! In another example, Blue Hubbard squash is planted around summer squash, reducing damage from cucumber beetles by 95%!
3. Sequential trap cropping installs attractive plants before high value crops; similar to nurse crops. Strawberries are protected against wireworms when wheat is planted in the same bed 8 days ahead of time.
4. Multiple trap cropping uses several species to lure pests throughout a valuable crop’s lifecycle. For example, flea beetles have been repelled when bunching green onions, dill, and marigolds are planted nearby, and stink bug and leaf-footed bug control is provided when a cash crop is surrounded with triticale, sorghum, millet, buckwheat, and sunflowers. [I imagine the local birds are pretty happy about it, too!]
5. Push-pull trap cropping surrounds a cash crop with an attractant, and intercrops it with a repellant. One highly effective combination, for growing corn, is to surround a field with fountain grasses (Pennisetum), and to intercrop with tick clover (Desmodium).
6. Dead-end trap cropping lures pests away from cash crops, but then fails to provide sustenance to the larval forms of the pests. Cowpeas and soybeans can be protected against bean pod borers by planting brown hemp (Crotalaria juncae, not the other hemp) nearby. If you have problems with Japanese beetles eating your roses, try installing Pelargonium geraniums nearby. The beetles will feed on the geraniums and die.
7. Semi-chemically assisted trap cropping uses kairomones, chemicals emitted by plants that attract pests, to lure pests into areas where they can be destroyed. This method is outside the home garden scenario.
8. Biological control assisted trap cropping lures beneficial predators to attractive perimeter crops, where they can then feed on the pests. For example, cotton fields may be surrounded with plantings of sorghum, providing protection against cotton bollworms. 
9. Genetically modified trap cropping uses genetically modified plants to make it possible to start growing earlier in the season, thereby avoiding infestation at vulnerable growth stages. In other cases, pests and disease resistance is built into the plant.

Very often, trap cropping methods are used in combination, improving their effectiveness. These methods reduce the need for chemical pesticides, while increasing biodiversity.

Which crops have the biggest pest problems in your garden? And how can you use trap cropping to protect them? Let us know in the Comments!