Researchers from the NWROC entomology project found soybean aphids on V1/V2 soybeans between Crookston and Fisher last week. Populations are very small so there is not reason to worry yet! This is the earliest date that soybean aphids have been recorded infesting fields in northern MN. These aphids moved into commercial soybean fields after successfully surviving as eggs on our local buckthorn

There were large populations of aphids on buckthorn last fall. Also, there were lower numbers of predators feeding on them in the buckthorn sites, contributing to large numbers of eggs being laid. Milder temperatures and snow cover during the past winter provided very good over wintering conditions for these aphids (Figure 1).

Buckthorn broke bud this spring around April 16. Newly hatched aphids were found at the same time. As buckthorn leaves expanded, the small aphids moved to the newest, smallest leaves. By early May, nymphs were already developing the wingbuds that would allow them as adults to migrate to soybean seedlings (Figure 2).

In the Crookston/Fisher fields, winged females were observed depositing nymphs on leaves and small colonies of several aphids were found on the top trifoliates of several plants (Figure 3). Populations are small at the moment but the weather conditions are conducive for aphid reproduction, and we are expecting these 'good aphid temperatures' to continue for at least the next week.

Remember, at this time of year all soybean aphids are females and reproduction is parthenogenic - asexual reproduction where female aphids are born 'pregnant' and when they mature, give birth to live daughters. These nymphs (young aphids) will mature in 3-10 days and then start having daughters of their own. Aphid populations are usually partially controlled by predation and by fungal diseases. However, our recent hot spell may have negatively impacted the fungal diseases that help keep these pests in check and the lack of rain may impair their ability to get established (like any other fungus, these insect killers need some humidity to establish and grow) We'll have to wait and see if this is the case.

Bottom line, it's not time to break out the spray rig yet but it is time to think about scouting your fields and keeping an eye on developing aphid populations. For information on early scouting for soybean aphids, go to the web at:

http://nwroc.umn.edu/ent/archives/early_sba2005.pdf