Two 30 x 100 ft plots of cowpeas were investigated as a trap crop, planted between a woods and peach orchard, as a management tool to reduce fruit injury from stink bugs. Stink bugs were attracted in large numbers (average as high as 9/plant) to potted cowpea plants introduced into each plot and baited with aggregation pheromone. Stink bugs did not move to planted cowpeas until beans formed about 7-10 days before peach harvest, but levels were much lower than that found on potted cowpeas. Brown stink bug was the most abundant species, followed by dusky and green stink bug, with peak populations occurring on plants from late June to early July. Inspection of peach trees revealed the presence of more stink bugs in rows adjacent to pea plots than in border rows on opposite (West and South) sides of the orchard without pea plots. Evaluation of fruit at harvest revealed a higher incidence of catfacing/scarring injury on trees adjacent to cowpea plots than on trees on opposite sides of the orchard without cowpea plots. Fruit injury in trees adjacent to cowpea plots would probably have been lower if the distance between the cowpea plots and orchard had been greater.
Three species of stink bugs [brown stink bug, Euschistus servus (Say); dusky stink bug, Euschistus tristigmus (Say); green stink bug, Acrosternum hilare (Say)] are major direct pests of peach in the Eastern U.S. Adult stink bugs overwinter under leaf litter, stones, tree bark, and logs in orchards and woodlands. Throughout the growing season, stink bugs move from weed and tree hosts to peach trees to inflict catfacing, scarring, watersoaked and gummosis type injuries to fruit. Injury near harvest can result in decay and fruit loss during storage, and may also contribute to fruit loss from brown rot, a fungal disease.
Orchards most likely to experience stink bug injury are those with poor weed control that are adjacent to woods and/or weedy borders. Stink bugs are very difficult to manage because they: 1) are highly mobile; 2) have a broad host range, including many crops and broadleaf weeds; 3) move frequently between weed hosts and peach trees; and 4) therefore, are not continually exposed to insecticide residues for long periods of time.
Peach growers have relied upon the application of insecticides to protect fruit from stink bug injury. Management has consisted of the application of pyrethroid insecticides at the very beginning of the season, followed by organophosphate insecticides for the remainder. The most efficacious organophosphate insecticide used much of the growing season was methyl parathion (Penncap-M). Its cancellation in 1999 due to FQPA resulted in increased use of pyrethroids for stink bug control. Although increased pyrethroid use reduced fruit injury by stink bugs, it also reduced insect predators, caused mite outbreaks, and increased the use of miticides. Since the cancellation of methyl parathion (Penncap-M), increased costs have occurred for miticide applications to decrease pyrethroid induced mite outbreaks, and for fungicide use to prevent fruit loss from brown rot resulting from stink bug injury near harvest. There is also concern about the potential of stink bugs to develop resistance to pyrethroids, which has already been demonstrated for stink bugs in soybeans. Other methods for management of stink bugs need to be developed in order to reduce fruit injury and dependence upon pyrethroid insecticides.
One alternative management method is the use of a trap crop, a highly desirable host plant that is used to attract and retain insects away from the peach trees. This method was investigated for stink bugs by entomologists in the mid-1990s in Mississippi. Cowpeas were used as a trap crop to attract stink bugs from a soybean patch that was harvested in order to prevent them from entering a pecan orchard. In this instance, the trap crop reduced stink bug injury to pecans by 50 percent. The idea which led to this project, was to use an aggregation pheromone lure in combination with cowpeas to produce a “super” attractive trap crop for managing stink bugs in peach.
- Demonstrate efficacy of a baited trap crop of cowpeas for attracting stink bugs.
Use a baited trap crop of cowpeas to improve fruit quality and reduce late season fruit losses from stink bugs.
Reduce dependence upon insecticides for stink bug control.
Delay development of insecticide resistance by stink bugs.
Reduce mite outbreaks and miticide application resulting from increased pyrethroid use to control stink bugs.
Conserve insect predator populations which have been reduced or eliminated by increased pyrethroid use.
Reduce insecticide residues on peach fruit.
Introduce fruit growers to concept of using a trap crop for insect control.
This study was conducted in an 8 acre Newhaven peach orchard in Hampshire County, West Virginia. The orchard is surrounded by woods and has an 8-year history of substantial fruit injury and loss from stink bugs. During late April, 2004, a 30 x 100 ft. plot was established at one end on the East and North side of the peach orchard between the edge of the orchard and the woods. Both plots were plowed, cultivated, and planted with pinkeye purple hull cowpeas using a one-row Earthway Garden Seeder on May 6-7, 2004. The pea plots were enclosed with bird netting supported by pressure treated posts, PVC “T-posts”, and high tensile wire to keep birds and deer from eating the plants. In addition, a Plotsaver system consisting of fiberglass stakes, poly-tape ribbon, and deer repellent was installed around the perimeter to provide extra protection from deer.
Beginning 2 weeks after planting, 15 potted cowpea plants that had been raised in a greenhouse were introduced into each plot. These potted cowpeas were used as a food source until the planted cowpeas had a chance to bloom and produce their own beans. A stink bug aggregation pheromone lure (methyl 2,4-decadienoate) was suspended from the netting above each potted cowpea plant. Potted cowpea plants were replenished as needed, generally every 2 weeks, and lures were replaced every 4 weeks. All potted cowpea plants were sampled for 10 consecutive weeks, beginning in June, to determine the number and species of stink bugs present. When the planted peas grew beans, they were also sampled by counting stink bugs inside a 27 inch diameter hula hoop that was randomly tossed in 5 areas of each pea plot. Pea plots were sprayed with formetanate hydrochloride (Carzol 92SP) on July 16, 2004 to kill stink bugs before they moved to peach trees near harvest.
All 4 sides of the peach orchard (2 with trap crop, 2 without) were also sampled weekly, beginning in June, and at harvest for fruit injury by stink bugs. Fifty fruit were examined on each of 4 trees in each of 4 rows (800 fruit total) at distances of 0, 10 or 15, 20 or 30, and 30 or 40 m from the orchard border. Fifty fruit were also picked from each sample tree at harvest on July 27, 2004, and evaluated for stink bug injury and incidence of brown rot.
Sampling of potted cowpea plants that were baited with aggregation pheromone lures revealed that stink bugs were highly attracted to these plants, averaging as high as 9 and 3.5 stink bugs per plant in plots 1 and 2, respectively. Populations peaked on potted cowpeas from late June to early July, with brown stink bug being the most abundant species, followed by dusky and green stink bugs. Stink bugs were not found on planted cowpeas until beans formed, about 7-10 days before fruit harvest, and numbers were less than on potted cowpeas. Stink bug numbers dropped significantly after Carzol was sprayed on July 16, 2004. Monitoring of stink bugs on border rows on each side of the orchard revealed higher abundance in trees adjacent to cowpea plots, than in trees on opposite sides of the orchard without cowpea plots.
Fruit were sampled and evaluated for stink bug injury on each side of the orchard from four rows at increasing distances from the orchard border. An average of rows adjacent to the two cowpea plots showed a slight trend towards increasing injury with increasing distance into the orchard, whereas injury was similar in all rows on the opposite sides of the orchard without cowpea plots. The average incidence of catfacing/scarring injury was almost 4% higher in trees adjacent to cowpea plots than in trees on opposite sides of the orchard without cowpea plots. Incidence of brown rot, which is aggravated by stink bug feeding, was significantly higher on trees adjacent to the cowpea plot on the East side of the orchard than on trees on the West side of the orchard without a cowpea plot. However, the reverse was true when comparing trees on the North side adjacent to the cowpea plot with trees on the South side without a cowpea plot.
Use of a baited trap crop of cowpeas was successful in attracting stink bugs. In addition to attraction into the cowpea plots, stink bugs were attracted in greater numbers to the border rows of peach trees adjacent to the cowpea plots, resulting in greater fruit injury as compared with trees that were not adjacent to cowpeas. It’s possible that the lures were drawing stink bugs away from the non trap crop side of the orchard, thereby lowering injury. It’s also possible that stink bugs attracted from the woods entered both the cowpea plots and the border rows of the peach orchard, resulting in higher fruit injury. This study provided 25 fruit growers with an opportunity to learn about the use of a trap crop as an alternative management strategy.
Education & Outreach Activities and Participation Summary
Twenty-five fruit growers were provided with an opportunity to tour cowpea plots as part of a Twilight Fruit Grower Meeting on June 24, 2004.
The farmer cooperator was very supportive of the project and is willing to continue use of a trap crop if changes can be made to demonstrate reduction in fruit injury.
Areas needing additional study
In order to fully understand the outcome, and make improvements in trap crop design, additional studies are needed to determine the specific reason why stink bugs respond to the aggregation pheromone and from what distance they are attracted. It may be that stink bugs are responding to the pheromone/trap crop for mating purposes, after which they return to the peach orchard to cause fruit injury. Additional studies should lead to a better understanding of how to use a trap crop in combination with a pheromone or other attractant to reduce fruit injury.