Definition & function

Webster's Dictionary (Guralnik 1980) defines "perimeter" as "the outer boundary of a figure or area" and as "a boundary strip where defenses are set up."  Perimeter trap cropping (PTC) involves planting a more attractive trap crop so that it completely encircles and protects the main cash crop like fortress walls.  The effectiveness of this trap crop system can usually be improved by adding other perimeter defenses, such as border sprays or with biological, mechanical and cultural controls.  PTC functions by intercepting pest migration, regardless of the direction of attack.  It then concentrates the pest population(s) in the border area, where they can be retained or killed, thus preserving natural enemies and reducing disease spread in the main crop. 

Small-plot results on cucumbers in 2003

In 2003, we evaluated a single trap crop row of Blue Hubbard, a border-row insecticide application, and a combination of the two strategies for protecting centrally-located unsprayed cucumbers from cucumber beetles and bacterial wilt.   The three treatments were compared to the center of unsprayed control plots consisting of all cucumbers.   

When the trap crop was sprayed it dramatically reduced defoliation on cucumber seedlings in the center and completely eliminated plant death due to direct feeding damage.  Nine percent of the plants were lost directly to beetle feeding in the center of control plots.  The sprayed trap crop barrier also reduced losses from bacterial wilt compared with the control plots.  Total plant death (directly from defoliation and from bacterial wilt) dropped from 30% in the center of control plots to 14% for the cucumbers in the sprayed trap crop plots by final harvest.  The sprayed PTC treatment increased yields by 33% or 148 boxes per acre.   At 2003 prices, this would be an increase in gross revenue of about $1,480/acre. 

Results on commercial farms in 2003

Four CT cucumber growers compared the PTC system to their former conventional cucumber beetle management system and were quite impressed.  In every case, the PTC system provided superior pest control compared to multiple full-field sprays and reduced insecticide use substantially.  Growers estimated they saved over 1/3 of their cucumber crop by switching to PTC.  One grower said that PTC cost him about the same amount of time and money as multiple full field sprays.  All the others said that the PTC system saved them time and money and they found it simpler to use than multiple full-field sprays.  

On most farms, insecticide sprays for cucumber beetles were limited to applications on the 'Blue Hubbard' trap crop in the perimeter of the fields only.  One of the growers stated on a post-season survey that "It blew my mind to see the beetles flock to the perimeter rows!"  

On one farm with extreme cucumber beetle populations, the grower normally applied 4 full-field sprays per field.  Despite the spraying, during the last few years he still failed to harvest or market any cucumbers due to cucumber beetle and bacterial wilt damage.  In 2003 using PTC, the grower applied an average of 1.5 perimeter sprays prior to bloom and 1.5 full-field sprays during harvest to two of his cucumber fields. After one perimeter spray in June, there was an average of 32 dead beetles per plant under the young trap crop plants and only 0.4 live beetles per plant on the unsprayed cucumbers!  One or two full-field sprays at harvest were necessary to prevent cosmetic damage, where the beetles feed on the fruit rind and render the crop unmarketable. The grower harvested and marketed a great crop of cucumbers in 2003 using PTC.  At an average price of $10 per box for a mix of (1/3) "Selects" and (2/3) "Super-selects," he increased his gross farm revenue by $3,810/acre of cucumbers. This same grower was asked to plant a control field (without a trap crop) as part of the study.  He made 4 full-field insecticide applications in the first 3 weeks and 60% of the plants showed signs of bacterial wilt before the plants even started to run. The control crop was lost!  When asked in a post-program survey to comment about the PTC system, this grower stated that "I can not even get a crop of cucumbers on my farm without PTC!" 

Perimeter Trap Cropping Recommendations

Growers wishing to try PTC should remember a few simple rules: 

1. Plant the trap crop on good ground, so that it remains healthy and completely encircles the main crop, without large gaps in the perimeter. Use the same in- and between-row spacing as the main crop.
2. Multiple rows (2-3) of trap crop may be needed if extreme pest pressure is expected, or along treelines where the heaviest pressure usually occurs as beetles colonize the field from overwintering sites. 
3. Spray the perimeter as soon as the beetles appear and begin to feed on the trap crop.  Do not wait for beetles to colonize the main crop or for a threshold level to be exceeded on the trap crop. 
4. Monitor the field continuously until bloom or harvest and be prepared to make 1-2 additional perimeter sprays or, if necessary, full-field applications.  Repeat perimeter applications are necessary if rain washes the insecticide from the plants prematurely or if more live beetles are found on the trap crop prior to bloom.  Full-field sprays should be applied when pest pressure is excessive on a particular farm, causing a breach in the perimeter and substantial main crop infestation (>1/2 beetle/plant for cucumbers). 
5. If the trap crop planting is incomplete or has large gaps in it, for any reason, treat the field as if it were a conventional planting (i.e. spray the whole field as often as needed).  You do not have an effective perimeter if you fail to plant along one side or wet conditions prevent emergence of most trap crop plants. 

We wish to thank NE SARE for funding this research.

click on images for a larger view which opens in a new window
Fig. 1.  'Blue Hubbard' (right) trapcrop protecting cucumbers		Fig. 2.   PTC cucumber field  at harvest time.
Fig. 3.  Dead cucumber beetles  under sprayed trap crop		Fig. 4.  Cucumber beetle feeding on fruit.
Fig. 5. Bacterial wilt on cucumbers		Fig.6. Increased yields with PTC