Trap crops are used to protect the main cash crop from a pest or complex of pests. The trap crop can be a different plant species, variety, or just a different growth stage of the same species as the main crop, as long as it is more attractive to the pests when they are present. Trap cropping is most worthwhile for pests that are abundant and destructive in most years. It tends to work best for insects of intermediate mobility rather than those, like aphids, that are passively dispersed by air currents or those strong fliers that descend on a crop from high elevations. Trap crops are more economical to use if the system is easily planted and maintained, if they have some other use (e.g. support beneficial insects or can also be marketed) and if they require a small amount of space relative to the main crop. The required trap crop planting size depends upon the intensity and direction of the pest attack expected, as well as the mobility of the target insect(s). Understanding how the pest uses and moves in its environment is crucial in developing or deploying a successful trap crop system.
Perimeter Trap Cropping (PTC) involves planting the attractive plant species so that it completely encircles the main crop like fortress walls. A trap crop barrier on all sides is useful when it is necessary to protect the crop from a pest attack that may come from several or unknown directions. This technique works best against pests that tend to damage the crop along the edge of the field (at least initially) rather than those that tend to have a random distribution throughout the crop. Wider trap plantings may be necessary along field edges that border known sources of infestation, such as insect overwintering sites, non-crop breeding sites or alternative food sources. For some pests, Perimeter Trap Cropping may work in very small (garden-size) plots but, for others, larger plantings may be required.
Perimeter Trap Cropping functions by concentrating and/or killing the pest in the border area, while reducing pest numbers and disease spread on the unsprayed cash crop in the center and by preserving natural enemies. The effectiveness of this trap crop technique can often be improved by adding other perimeter defenses like biological, mechanical, cultural or chemical control tactics (i.e. border sprays), or with pest attractants and repellants. The perimeter orientation of the trap crop and defenses improves efficacy because the barrier intercepts the pest migration regardless of the direction of attack, rather than trying to get the pest to move to where you want it to go. The technique may not always eliminate the pest completely, but it can substantially reduce their populations on the main crop. In recent years, Perimeter Trap Cropping has dramatically increased the efficacy of trap cropping on a variety of crops.
What can Perimeter Trap Cropping do for you?
- Less spraying usually translates into lower costs.
- Less spraying simplifies harvesting and marketing, by eliminating re-entry (REI) and pre-harvest restrictions (dh).
- Less spraying reduces the possibility of chemical residues at harvest.
- Less spraying leads to fewer environmental and safety concerns.
- Less spraying may help improve personnel/management relations. This is especially true for migrant labor crews, who may be distrustful of management and of pesticide applications.
- Less spraying delays the development of pesticide resistance.
Collards around cabbage (Fig. 1) The diamondback moth (DBM) becomes resistant to insecticides quickly and is therefor difficult to control. Researchers in Florida were able to keep the DBM from reaching action thresholds in nine commercial cabbage fields by surrounded them with two rows of collards. Sixty percent of the nearby control fields without collards exceeded thresholds. The DBM population on the collard plants around the cabbage exceeded threshold in 89% of the fields, but a naturally occurring parasitic wasp, Diadegma insulare, helped control the population and keep it from spilling over into the cabbage. Perimeter trap crop fields used 56% fewer insecticide sprays (there were sprays for loopers) for a net savings of $117 - $156/hectare in chemical costs.
Cherry peppers around bells (Fig. 2). Researchers in Connecticut attempted to stop pepper maggots from infesting bell peppers by trying border sprays, a perimeter trap crop of hot cherry peppers and a combination of the two methods. Bell peppers surrounded by the trap crop produced at least 98% pest-free fruit at harvest compared with all-bell plots which had 15% of the fruit infested. Commercial farmers using Perimeter Trap Cropping harvested 99.99% clean fruit, experienced the best pest control in the history of the farms, and better pest control than farms that had used well-timed full-field sprays. They reduced their insecticide use on peppers by up to 89%. Growers said the system simplified pest control and saved them money. Economic analysis confirmed an overall improvement in crop profitability ($13 - $378/hectare).
Blue Hubbard around yellow summer squash. (Fig. 3). Connecticut researchers attempted to stop cucumber beetles and squash vine borers damage on summer squash with perimeter trap crops and different combinations of supplemental controls in the border area. Over 94% of the cucumber beetles in the experiment were on plants in the perimeter. Beetle populations on the unsprayed main crop in the center were reduced by up to 95%. Spraying the perimeter trap crop reduced squash vine borer infestation on the unsprayed summer squash within by 88%. Six commercial cucurbit growers successfully employed the technique in 2002. All the growers improved their pest control and reduced crop damage using Perimeter Trap Cropping, and all said they would continue to use trap crops in the future.
T. Jude Boucher, Agricultural Educator-Commercial Vegetable Crops,
Robert Durgy, Research Assistant, Integrated Pest Management & Nutrient Management
UConn Cooperative Extension, Vernon, CT
This research is supported by grants from the USDA NE-IPM & NE-SARE Programs and the New England Vegetable & Berry Growers' Association.
Fig. 3. Blue Hubbard around yellow summer squash
Photos shown above by T. Jude Boucher, University of Connecticut
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