The soybean aphid is one of the greatest agricultural pests in Minnesota.8 When infestations grow out of control, management and insecticide applications can become very costly. Some populations have also become resistant to pyrethroid insecticides which can add additional expenses. Fields that are most susceptible to early aphid infestations often have abundant common (or European) buckthorn in their wooded borders.
Buckthorn is the overwintering host for soybean aphids, and during the late spring/early summer these insects can make the short journey to nearby soybean plants.7 There is nothing worse than finding your field with high numbers of aphids much earlier than expected. Buckthorn removal has potential benefits to your wooded lot, but unfortunately buckthorn removal will not prevent aphid problems over the season. Still, identifying if your land is abundant with buckthorn might help you target fields for early aphid scouting.
Common Buckthorn Profile
Common buckthorn (Rhamnus cathartica) is an invasive species and a Restricted Noxious Weed in Minnesota. Buckthorn can be identified as a tall shrub which covers wooded areas in dense thickets of its spreading branches. Spread by birds into new areas, buckthorn crowds and shades out native plants and shrubs.3 Buckthorn does this by leafing out earlier and keeping its leaves later into fall.
Why implement earlier scouting?
As the overwintering host, nearby buckthorn gives aphids easy and early access to your soybean crop. This scouting should occur around early June as aphids can colonize plants as early as May 13 (Fig.1). Focusing earlier scouting efforts on fields with known nearby buckthorn can allow you to identify potential problem areas and facilitate more timely management of infestations. This helps eliminate the possibility of being surprised later in the season with infestations past the threshold of 250 aphids per plant.13 If necessary, speed scouting can be an acceptable, but a less accurate substitute for traditional whole plant counts. Regardless of what scouting method you choose, identifying when economic thresholds are met is critical.
Buckthorn removal limitations
While seemingly simple, removing all common buckthorn (whether by herbicide treatments, physical removal, or goats) is not a practical solution to stop soybean aphids in Minnesota. Aphids can drift in from far away areas—traveling up to six miles per day4—and large buckthorn populations can be on others’ land and outside of our control.
Traditional Buckthorn Treatments
Most traditional removal techniques involve chemical treatment. Cutting the stems and applying herbicide to the cut area is very common. Other treatments exist, such as spraying herbicide on the bark or onto the leaves, but all are time consuming and labor-intensive. Deciding if buckthorn removal is right for you and your operations can be tricky.
UMN Extension produced several videos for planning and managing buckthorn removal that may be helpful.
Source: umn.edu
Photo Credit: istock-fotokostic
Categories: Minnesota, Crops, Soybeans