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 long as it is more attractive than the main crop to the pests when they are present.Trap cropping is most worthwhile for pests that are abundant and destructive in most years. This method works best for insects of intermediate mobility. It is less effective on insects, 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; they have some other use (e.g., to support beneficial insects or as a marketable crop); and 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). For some pests, trap cropping may work in very small (garden-sized) plots but, for others, larger plantings may be required.
Understanding how the insect uses and moves in its environment is crucial in developing or deploying a successful vegetables trap crop system.Wider trap plantings may be necessary along field edges that border known sources of infestation, such as insect overwintering sites, noncrop breeding sites or alternative food sources.The effectiveness of trap cropping can often be improved when used in conjunction with chemical, biological, mechanical or cultural control tactics or with pest attractants and repellants.
Perimeter trap cropping involves planting the attractive plant species so that it completely encircles the main crop like fortress walls. Perimeter trap cropping is useful when it is necessary to protect the crop from a pest attack that may come from several or unknown directions. It is probably the most conservative way to use a trap crop and, because the attractive plant species or variety must completely surround the main crop, it may require that more of the field be dedicated to the production of the trap crop. However, because the edge to area ratio shrinks the bigger the field gets, perimeter trap cropping is more economical for larger plantings (i.e., proportionally less area is dedicated to the trap crop).Also, if you intend to market the trap crop,many of the increased costs associated with making the protective perimeter planting are eliminated because they are costs that would have been incurred on the main crop anyway.
If perimeter trap cropping is right for your situation, and you intend to attempt this method, you must maintain the health and attractiveness of the trap crop throughout the time the pest may be migrating into the field. In addition, you should have a complete perimeter,without gaps or holes. In some cases where perimeter trap cropping was tried, the barrier was not completely closed around the main crop.This caused the pest to pour through the open gap like water into a leaky boat or an invading army into a castle on an open drawbridge. Failing to plant or maintain an unbroken perimeter is the primary reason for poor results.
Why use perimeter trap cropping?
Perimeter trap cropping for pepper maggots.
Perimeter trap cropping canbe used to protect bell and other sweet peppers from low to moderate pepper maggot population pressure (Fig. 1). Perimeter trap cropping may not eliminate pepper maggots completely, but it has been shown to reduce maggot infestations dramatically and to lower pesticide use. Researchers have found that when unsprayed hot cherry peppers are used as a trap crop to protect sweet bell plantings, up to 92% of the fruit infestation occurs on the perimeter trap plants. When the hot cherry pepper trap crop plants are treated with an insecticide to coincide with the flight of the adult pepper maggot fly, infestations on the unsprayed main crop (bells) are reduced. This reduction is by 98 to 100% compared with all bell plantings left unprotected (Fig. 2). Connecticut commercial growers had success with this technique on plantings as small as 1/4 acre and as large as 20 acres. Growers,who have used perimeter trap cropping to supplement their current IPM practices, have reduced their pesticide use on peppers by up to 99%, compared with their pre-IPM pesticide use. They have experienced the best insect control in the history of their farms, as well.
Occasionally, pepper maggot populations will build to extremely high levels in conventional pepper production. This is because of the constant presence of the host crop (peppers, eggplant or horse nettle) and the pest for many years, and a lack of proper control procedures. If artificially high pepper maggot populations exist on a farm, it may be advisable to lower the population with a series of welltimed pesticide applications for a year or two, before attempting perimeter trap cropping for this pest. Also, this technique will not work if horse nettle is allowed to grow freely within the perimeter, although it has worked when growers plant other highly attractive varieties as part of their main crop (though, this is not advisable).
What you need to know about the pepper maggot.
This pest is not present on all farms, but it is common to many farms in states along the Atlantic seaboard, from Massachusetts to Florida. It occurs as far west as Ontario and Texas.You want to confirm that your farm or field is absolutely pepper maggot-free (see "monitoring") before switching to a low-spray IPM program that relies on selective materials for caterpillar control.The environmentally sound alternative is to use perimeter trap cropping. Specific pepper varieties such as hot cherries, 'Apple' pimiento and 'Espana' are among its favorite hosts, although it will infest other fruit as well, especially round or blocky-shaped varieties, eggplant, and the fruit of its natural host, horse nettle. Therefore, it is important to use a complete IPM package including crop rotation and proper weed management to help eliminate horse nettle from your fields.
Pepper maggots survive the winter as pupae in the soil where Solanaceous crops or horse nettle grew the previous season. They have a single generation each year and the flies (Fig. 3) usually emerge from the soil beginning in early to mid-July in southern New England. The flies are mobile insects, but tend to forage for food in the canopy of nearby trees, especially maples, before moving into the field to mate and lay eggs (Fig. 4). The flies enter the field from the bottom of the tree canopy and infest plants along the edge of the tree line first, before moving from plant to plant deeper into the pepper field. Some flies may move from trees further away, across open fields or other crops, to infest the far end of a pepper block, away from the closest tree line. Over 90% of the flies emerge during the first 2 weeks, but they can live for a month or more, and a few may still be present in late August.
Pepper maggot flies can be monitored using traps or indicator plants. Ammonia-baited (28%), yellow, sticky traps (Fig. 5) can be hung approximately 20 feet high in the canopy of a nearby maple tree. Climbing steps that screw into the tree trunk make the task of hanging and checking the trap much easier. A simpler method involves planting indicator plants of hot cherry peppers at intervals of 25 yards in the outer rows of your pepper planting and checking the surface of fruit for oviposition scars (egg-laying stings) through the month of July (Fig. 6). Since you will presumably have cherry peppers in the outer rows of your planting as your perimeter trap crop, the latter method of monitoring is the obvious choice for simplicity.
The hot cherry pepper seedlings can be machine transplanted on two sides of the field. At the same time, two or four transplants should be set by hand at the end of each row or bed to provide a barrier on the third and fourth sides. One grower had his transplant crew hand plant the trap crop at the end of each row while the tractor turned around, and estimated his labor costs to plant the barrier at zero. Use the same within and between row trap crop spacing as your main crop. Transplant the trap crop at the same time as the main crop and provide both with similar fertilizer, irrigation and weed control programs. There is no need to plant the trap crop at the opening of spray alleys. Experience has shown that the flies do not tend to use the unprotected alleys to penetrate the field perimeter.
Depending upon the degree of pest pressure expected, it may be necessary to plant a trap crop border of up to 20 or 30 feet along a nearby tree line where the heaviest pest pressure and damage is likely to occur. A narrower planting of one or two trap crop rows usually suffices along borders that are not immediately adjacent to trees. When population pressure was low to moderate, commercial growers have experienced perfect control with two trap crop rows around the whole field and one or two well-timed border sprays. Commercial border sprays have targeted a 20 to 25 foot swath around the field to accommodate mist blowers or large boom sprayers. However, the technique has worked well in large research plots when insecticides were applied only to the three outside trap crop rows with a backpack sprayer. Moderate to high pest pressure definitely requires two or three border insecticide treatments to maintain crop quality.
Perimeter trap cropping allows you to limit (or eliminate) broad-spectrum insecticide applications to the border plants, leaving most of the cash crop planting unsprayed, and preserves most of the beneficials that help control secondary pests like aphids. Lady beetles and other beneficials also consume more than half the European corn borer eggs in the field.
At this time, there are no selective insecticides that have proven effective against the pepper maggot. If you choose to use a pesticide on your perimeter trap crop, a systemic insecticide is recommended to kill both the adult flies and the larvae that hatch from eggs inserted under the fruit surface. Both dimethoate and acephate (i.e. Orthene) are effective on pepper maggots for at least 8 to 10 days.Dimethoate is registered for use against the pepper maggot. Acephate is registered for use on peppers against aphids, European corn borers and others and can be used if these pests are present in the field at the same time as the pepper maggot. Sprays should target the adult pepper maggot flies as they enter the field (when cherry peppers begin to be stung), and be reapplied through the entire period of fly emergence, if necessary.Usually, one or two applications are sufficient.Growers planning to market the cherry pepper fruit should spray the border trap crop to preserve fruit quality.
T. Jude Boucher, Agricultural Educator - Commercial Vegetables, University of Connecticut
Rob Durgy, Cooperative Extension System, University of Connecticut
(All photos in this article by T.J. Boucher)
Supported by a grant from the U.S.D.A. Northeast Integrated Pest Management Program
Yankee Grower, New England Journal for Profitable Horticulture. Vol. 4, No. 1 Year 2002 p.8-11
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