With the cool, wet weather, soybean aphid development will be slow this spring. No soybean aphid colonies have been observed on their overwintering host, buckthorn, in the southern Red River Valley of North Dakota. In other north central states, Wisconsin has reported low numbers of colonies with only wingless adults and nymphs, no winged aphids, and few natural enemies on buckthorn. Dr. David Voegtlin, Illinois Natural History Survey, conducted his annual spring survey for soybean aphids on buckthorn in Indiana and Michigan. He found the majority of locations had no soybean aphids and only a few sites had low numbers of colonies.
Data from the North Central Regional Soybean Aphid Suction Trap Network provides the population density of soybean aphid fall-migrations to the public. These data provide an indication of spring flight from buckthorn to soybean in the spring. Low soybean aphid flight in the fall may correspond to low soybean aphid flights in the spring. However, several other factors are known to impact aphid populations in the spring and fall, such as weather entomopathogenic fungi and natural enemies (predators and parasitoids). Neighboring state's suction trap surveys (four traps in Minnesota and one in South Dakota) also reported very low numbers of soybean aphids captured last fall. These results are comparable to most of the other traps in the North Central Region. The Web site is here.
Although North Dakota is not included in the spring soybean aphid on buckthorn survey or suction trap netowrk, we are expecting low numbers of soybean aphids early in the season due to the low populations of overwintering soybean aphids. With the late planting of soybeans, we will need to scout for soybean aphids later in the season (early July through August) as local populations can build quickly if environmental conditions become more favorable (moderate temperatures in 70s and 80s F and dryer conditions) for aphid reproduction, and as migrants may be blown into North Dakota from southern states. But for now, this is good news for soybean producers.