Perimeter Trap Cropping for Yellow and Green Summer Squash
Perimeter Trap Cropping (PTC) involves planting trap crop plants so that they completely encircle the main cash crop like fortress walls, and the use of other perimeter defenses, if necessary. PTC 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.
Perimeter Trap Cropping for yellow and green summer squash. A perimeter trap crop of Blue Hubbard squash can be used to protect summer squash from low to moderate populations of striped and spotted cucumber beetles (Fig. 1 & 2) and squash vine borers (SVB) (Fig.3). Controlling cucumber beetles is the key to managing bacterial wilt, caused by Erwinia tracheiphila, which is transmitted by the beetles. Cucumber beetles can also transmit mosaic viruses and have been shown to increase the spread of powdery mildew and black rot between plants. Cucumber beetle larvae, which feed on the roots of squash plants, have been associated with fusarium wilt epidemics. Preserving natural enemies may also help prevent outbreaks of secondary pests, such as aphids, the prime vectors of viruses to squash.
Preliminary research in Connecticut has shown that PTC can reduce pesticide use, while lowering cucumber beetle and SVB infestations on summer squash by up to 95% and 88%, respectively. Six commercial cucurbit growers successfully employed the PTC technique in 2002. All the growers improved their pest control and reduced crop damage using PTC, and all said they would continue to use trap crops in the future.
Planting Blue Hubbard around summer squash. Use the same in- and between- row spacing to plant the main crop of summer squash and the perimeter trap crop row (or rows) of Blue Hubbard. Whether direct seeding a bare-ground block or transplanting into mulched beds, plant the outside rows along the length of the block by machine. Trap crop plants (1-4) at the end of each row can be planted by hand or with the aid of machinery. If machine transplanting into mulched beds, simply leave 2-4 holes empty at the end of each bed while planting the main crop, and send a worker back with a flat of trap crop plants to fill in the holes and complete the perimeter barrier. If direct seeding a bare-ground block, simply turn the planter perpendicular (sideways) to the summer squash rows and seed trap crop plants across the ends of the rows. Don't worry if all the Blue Hubbard plants don't line up with the summer squash rows, or if some of the trap crop plants are injured or killed later by cultivation or tractor tires. As long as most of the trap crop plants survive on all four sides of the field, without major gaps (> 15 feet), the barrier should still function.
In dry soil conditions, without the benefit of irrigation, the larger Blue Hubbard seed may take longer to imbibe water, germinate and emerge, than the smaller summer squash seeds/plants. Plant the trap crop one week prior to the main crop in dry conditions or in shady areas along field margins. With adequate soil moisture and sun the two crops should emerge simultaneously.
Managing cucumber beetle populations with PTC. If possible, rotate summer squash plantings to a field at least 1/2 mile from the previous season's cucurbit crop plantings to help reduce the size of the cucumber beetle population. Simply rotating within a field or to an adjacent field does not reduce the beetle population. Begin scouting outer trap crop rows for cucumber beetles as soon as the plants emerge or within days of completing transplant operations (Fig. 4). While scouting, pay particular attention to trap crop rows that border tree lines or hedgerows, which are likely sites of early colonization, due to the proximity to prime beetle overwintering habitat. Scout for beetles twice weekly. Treat perimeter trap crop rows with an effective insecticide as soon as the first beetles are found. From 1-3 weekly applications may be necessary depending upon weather conditions and the size of the beetle population. If heavy rains remove the insecticide soon after application, reapply it as soon as possible. Try to prevent the beetle population from killing and overrunning the perimeter plants. It is crucial to maintain the health and attractiveness of the trap crop plants for the barrier to function. This system will control low to moderate beetle populations (0.1-5.0 beetles/trap crop plant), but additional management strategies may be necessary for unrotated fields with higher beetle populations. Green summer squash (zucchini) is more attractive to the beetles than yellow, and may need to be treated along with the trap crop when beetle pressure is moderately-high (3-5 beetles/trap crop plant).
Organic growers may substitute products with pyrethrin or rotenone for synthetic insecticides, or may supplement the PTC system by applying kaolin clay (i.e. Surround) to the summer squash to help repel the beetles. Botanical insecticides tend to have a short residual period of effectiveness, necessitating more frequent re-application of the insecticides. Caution: an unsprayed trap crop border will help concentrate and hold low beetle populations (0.1-1.5 beetles/trap crop plant) in the perimeter, but moderate populations will redistribute throughout the field in a random fashion over time.
Managing squash vine borer populations with PTC. The adult SVB moth (Fig. 5) visits perimeter trap crop plants while migrating into the summer squash. The perimeter trap crop row(s) must be sprayed during the adult flight to kill the moths and prevent oviposition (egg laying) on summer squash plants (Fig. 6 ). Time 3-4 weekly insecticide applications (i.e. Asana) with the adult moth flight. Moths can be monitored with a Scentry Heliothis Trap (Fig. 7) and Hercon brand SVB pheromone lure. One lure will last all season and extra lures can be stored in a freezer for many years. Monitor with traps from mid-June through early August. Hang the trap so that the bottom is almost touching the squash plants. Stretch the cloth strap across the opening, so that it is level with the bottom of the trap, and attach the lure to the strap with a safety pin. Empty the (top) capture chamber weekly and count the SVB moths. Spray the Blue Hubbard trap crop if you find more than 5 SVB moths/week in the trap. Adult SVB moths are about an inch long, have dark (brown to black) scales on the wings and bright orange scales on the legs and the top of the abdomen.
Some PTC recommendations and warnings to remember.
- If possible, rotate your field to reduce beetle populations and because some beetles may overwinter under plant debris in old cucurbit fields (perimeter may be breached from the start).
- The trap crop must completely encircle the summer squash, without large breaks in the perimeter, or the system will not stop the invading army of insects.
- If moderately-high beetle populations (3-5 beetles/trap crop plant) are expected, fields may need a wider trap crop barrier (multiple rows), at least along wooded borders or hedgerows where beetles tend to overwinter. Colonization pressure is the highest near overwintering sites.
- In dry soil conditions, plant the trap crop a week before the summer squash, because the larger Blue Hubbard seeds will require more time to absorb enough water to germinate. The trap crop should emerge simultaneously with (or before) the summer squash, and will with adequate soil moisture.
- Additional perimeter defenses (i.e. trap crop border sprays) will be required for moderate to moderately-high cucumber beetle populations and to control SVB. Failure to use an insecticide with moderate pressure could result in heavy cucumber beetle and bacterial wilt damage.
- Trap crop insecticide applications should be timed to protect newly emerged seedlings as soon as beetles have arrived from overwintering sites. Additional perimeter sprays may be needed to assure plant establishment, control bacterial wilt (may need to spray until first bloom), or control SVB infestations.
- Planting other, unrelated crops, in "traditional spray or harvest alleys" may prevent the use of an effective insecticide (if unregistered on the second crop) for beetle control. Use of an ineffective insecticide may not control the pest(s) or reduce insecticide use.
- Planting other related crops (mixed cucurbit planting) may cause a breach in the perimeter, as some cucurbit crops are more attractive than others.
- Never use a trap crop (i.e. Turk's Turbin) that is a major reservoir for the bacterial wilt pathogen. A trap crop disease reservoir can lead to increased bacterial wilt incidence and lower yields.
- PTC will work in small garden-size plots (20 x 20 feet) of summer squash, but becomes more cost effective as the field size increases. PTC has worked in 5-acre summer squash fields and in even larger cabbage and pepper fields against other pests.
- Square blocks or wide rectangles may work better than long, lean, rectangular PTC plantings. Wider blocks may allow insecticide applications to the outer (trap and main crop) rows to be made by machine (circle the field once). If only a few long rows are used in the PTC block, a backpack sprayer may be required to treat the trap crop and avoid spraying the entire summer squash planting.
- Irregular-shaped fields can sometimes make it difficult to plant an unbroken trap crop barrier along all four sides of the field. For example, planting a few (1-4) trap crop plants at the end of each mulched bed does not form an effective barrier, if the beds get progressively shorter along one side of the field. Cucumber beetles and SVB moths will migrate in through large gaps in the perimeter barrier.
- Try to use fields with fairly uniform soil types and slopes to assure a timely emergence of the trap crop. Avoid planting the trap crop barrier in low "wet holes" or along a margin of the field that may flood and leave large gaps in the perimeter.
- The most important rule to remember is; don't just plant your summer squash PTC system and forget about it. You must continue to monitor the pest populations to know if additional control measures are warranted (i.e. on green squash or with high beetle populations).
Photos shown above by Robert Durgy, University of Connecticut
By: T. Jude Boucher, Agricultural Educator-Commercial Vegetable Crops, Robert Durgy, Research Assistant, Integrated Pest Management & Nutrient Management, UConn Cooperative Extension, Vernon, CT. 2003. Reviewed 2012.
This research was supported by grants from the USDA Northeast Sustainable Agriculture Research & Education (NE-SARE) and Northeast Integrated Pest Management (NE-IPM) Programs.
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