By Anya Osatuke, Berry Specialist, Cornell Cooperative Extension Harvest New York
A trap crop is a crop grown alongside a cash crop. The trap crop is more attractive to pests than the cash crop and is used to lure the pests away from the cash crop. To be profitable, trap crop plantings are small and easy to manage. These plantings may also attract beneficial insects or yield marketable fruit.
Trap crops can be used for scouting and can inform pesticide applications. Two effective trap crops for berry plantings are raspberries, which attract spotted wing drosophila, and red and white currants, which attract aphids and the beneficial insects that eat aphids.
Raspberries are a preferred host of spotted wing drosophila, a notorious pest of blueberries, tart cherries, and fall-bearing strawberries. The spotted wing drosophila begins to emerge between May and July, and populations are usually well established by August. Raspberries that are producing fruit in the early summer can attract spotted wing drosophila away from other berry crops while populations are still low. When pressure is high, as in the late summer and fall, raspberry fruit is likely to serve as a breeding ground for spotted wing drosophila and should be managed very intensively to avoid increasing the local population of pests. Careful monitoring of raspberry fruit quality though salt flotations can help determine the status of the pest population on-farm. When infestation levels are high (10 larvae or more per 50 fruit) in raspberries, assume high pest pressure to all susceptible crops. Infested raspberry fruit can either be treated by harvesting and disposing of all fruit in a sealed bag, or a targeted pesticide application may be made to the raspberry patch on regular intervals.
Red and white currant bushes are highly tolerant of aphid feeding, and do not have reduced yields even under high pressure. When aphids attack, the currant leaves become bumpy and dark red, giving a clear visual indicator of the aphids’ presence. The species of aphid that prefers currants, the currant blister aphid, is just one of hundreds of species of this pest. The benefit of currants is their ability to harbor huge colonies of aphids that feed only on the currant, and attract beneficial insects that eat all species of aphids such as ladybugs and lacewings. These beneficial predators will make their way to the currant bushes within a week or so after the aphids. Red and white currants are salt-tolerant and can be planted as hedgerow bordering salt-sensitive berry crops such as blueberries. In addition, deer and birds tend to eat currants less often than other berry crops. These traits make currants a great option for a single or double-row border to protect the desired crop from road salt and pests.
References and further reading
T. Jude Boucher, University of Connecticut Integrative Pest Management: Perimeter Trap Cropping Works! 2012. lhttps://ipm.cahnr.uconn.edu/perimeter-trap-cropping-works/
Anonymous, Royal Horticultural Society: Currant blister aphid. N.d. https://www.rhs.org.uk/biodiversity/currant-blister-aphid
C. E. Frank Sullivan, M. Skinner. Entomology Research Laboratory, University of Vermont: Plant- Mediated IPM Systems Explained. 2013. https://www.uvm.edu/~entlab/Greenhouse%20IPM/Workshops/2014/PlantMedlIPMSystemsOverviewFinalNov13.pdf
J. Jasinski, The Ohio State University Extension IPM Program. Salt Water Test for Spotted Wing Drosophila (SWD) Larvae. 2017. https://cpb-us- w2.wpmucdn.com/u.osu.edu/dist/1/8311/files/2017/04/SWD-salttesthandout-updated-pnd335.pdf