Cookies are OK, but I really like ice cream. It turns out that insects
have food preferences, too. Extension specialists are working to understand
those preferences, and put them to work in a new tool for managing vegetable
insect pests, called Perimeter Trap Cropping, or PTC. For the past
few years, Jude Boucher of the University of Connecticut Cooperative Extension
and Ruth Hazzard of University of Massachusetts Extension have studied
PTC by conducting trials on research farms and in grower’s fields.
Trap cropping is not a new idea. Many growers and gardeners have
planted traps crops to protect a main cash crop from a pest. To be effective,
a trap crop has to be more attractive to the pest that the cash crop. Depending
on the situation, a trap crop can be a different plant species, variety,
or just at a different stage of growth than the cash crop. Trap crops work
best on pests that are abundant and destructive just about every year,
rather than for pests that only appear once in a while in your location.
What’s new about PTC is how the trap crop is managed. In the past,
growers tended to plant a single row of a trap crop next to a cash crop.
With PTC, the trap crop is planted to completely encircle the cash
crop, like a fortress wall. Pests are intercepted along the border,
regardless of the direction of attack. This simple redesign of the crop
production system works equally well on large and small farms and is easy
to use because the same machinery, crop spacing, and plant-culture system
can be used for both the cash crop and trap crop.
Because PTC concentrates the pest in the border area, the effectiveness
of this technique can often be improved by spraying the border as soon
as the pest arrives. This prevents pests from moving into the main crop.
Border sprays require significantly less time and pesticide compared to
full field sprays. By avoiding cover sprays in the main crop, natural enemies
are protected, too. PTC with border sprays may not eliminate the pest completely,
but it can substantially reduce their populations on the main crop.
Blue hubbard squash has been used in many of the PTC studies so far.
It was selected as a trap crop for other cucurbit crops because it is highly
attractive to striped cucumber beetles, has vigorous seedlings, and is
not as susceptible to bacterial wilt as other attractive varieties.
Blue Hubbard around yellow summer squash has been studied for several
years in Connecticut. In experimental plots, over 94% of all the cucumber
beetles were found on plants in the perimeter. Beetle populations on the
unsprayed main crop in the center of the plots were reduced by up to 93%
where sprays were applied to the Hubbard squash border, compared to plots
without perimeter sprays or trap crops. Spraying the perimeter trap crop
also reduced squash vine borer infestation on the unsprayed summer squash
inside the plots by 88%. Six commercial growers employed this technique
in 2002 and 2003, and all of them improved their pest control and reduced
crop damage. All but one said the system was simpler to use and saved them
time and money. Blue Hubbard works equally well around cucumbers or melons.
In Massachusetts, experimental plots planted in 2003 with Blue Hubbard
borders had eight times as many cucumber beetles per plant in the border
than those with butternut at the border. The number of beetles per plant
in the unsprayed main crop was reduced by 60% where there were sprayed
Blue Hubbard borders, compared to the control. The same system was tested
in six commercial fields of butternut ranging in size from two to six acres.
On average, more than seven times as many beetles per plant were found
in the borders of protected fields than on the main crop. At one point
over a hundred beetles were counted on one plant in the border. Fortunately,
the border had recently been sprayed and most of them were dead. Unfortunately,
a combination of heavy rains and cold, wet soils led to poor crop emergence
and the incomplete borders did not hold up against the beetles. In several
cases growers needed to use a full-field spray because of the combination
of high beetle pressure and poor trap crop emergence. It may be necessary
to use a double border along woods edges, and possibly a systemic insecticide
treatment to help keep the borders intact enough to protect the main crop
even in times of extremely high beetle pressure.
PTC can also be implemented using a different variety of the main
crop species in the border. Prizewinner, a giant pumpkin variety, is highly
attractive to cucumber beetles – more attractive than standard pumpkins.
One grower in 2003 planted Prizewinner as a perimeter around a field with
a mix of other pumpkin varieties as the main crop. Despite the fact that
half the field was planted late due to the wet weather, the beetles were
heavily concentrated on the border plants. There were three times the numbers
of beetles in the border than in the main crop. The grower sprayed the
border three times, did not spray the main crop, and was satisfied with
his control in the main field.
Cabbage is another crop that may be protected by PTC. Researchers
in Florida were able to keep the diamondback moth from reaching action
thresholds in nine commercial cabbage fields by surrounded them with two
rows of collards. In Massachusetts, it seems that imported cabbageworms
also prefer collards to cabbage. A 25% reduction in the number of cabbageworm
larvae was measured in the main crop of the plots with a perimeter of collards
vs. the plots without PTC collard borders.
Pepper maggot flies lay their eggs in pepper fruit and the maggots
feed inside, ruining the fruit. This pests is worse on some farms or fields
than others, and only occurs as far north as southern New England. Pepper
maggot flies prefer to lay eggs in cherry peppers, compared to regular
bell pepper. Researchers in Connecticut have stopped pepper maggots from
infesting bell peppers by using a perimeter trap crop of hot cherry peppers
and border sprays timed when flies begin to sting the fruit in the border.
In experiments, 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 PTC harvested 99.99%
clean pepper fruit, and had better pest control than farms that had used
well-timed full-field sprays. They reduced their insecticide use and reported
improvement in crop profitability ranging from $5 to $152 per acre.
Results from experiments in Connecticut also indicate that both Colorado
potato beetle (CPB) and eggplant flea beetle (FB) prefer the elongated
Italian or Japanese eggplant, ‘Vittoria’ compared to standard eggplant
varieties and to tomato. If either of these are a problem on your eggplant
or your tomato, using Vittoria as a PTC may help, although results are
not yet conclusive. Border plants can be sprayed when FB or CPB arrives,
or could be treated with a systemic insecticide before transplanting.
PTC may also work with potatoes around potatoes. Since Colorado potato
beetles emerge in the field edges and walk or fly into potato fields, an
early-planted or early-emerging crop that is planted along the border can
serve as a trap crop. Early emergence can be achieved by green sprouting
the potatoes before planting. Another option is to plant an early variety
such as Superior two weeks before the rest of the crop.
PTC is in its early stages of development, but shows great promise.
If you’d like to try it, here are some tips for success. First, be sure
to plant the trap crop on good ground where it will grow well, and sow
it to completely encircle the cash crop, without any gaps, even in an irregular
shaped field. The trap crop can be planted with your regular planter, or
by hand. Drive a planter across the ends of the rows, in order to plant
crosswise. If you have to cultivate out some plants in the row middles,
don’t worry about it. Multiple trap crop rows may be needed, especially
near woods where the pest has over-wintered, to prevent large populations
of migrating pests from breaching the trap crop barrier.
Scout the border rows frequently and spray the perimeter as soon
as beetles (or other pest) appears and begins to feed on the trap crop.
Don’t wait to get to a threshold of pest numbers. Use PTC along with crop
rotation and other cultural practices to reduce pest populations. Don’t
expect PTC to provide perfect control with extreme pest populations.
There are several articles with more details about PTC located on
the web at: http://www.ipm.uconn.edu/pa_vegetable/.