Cropping Issues in Northwest Minnesota

Angie Peltier, UMN Extension crops educator; Bob Koch, UMN Extension soybean entomologist; and Bruce Potter, UMN IPM specialist Caterpillar identification 101.   The moths that lay eggs that eventually hatch into green cloverworms ( Figure 1 ) and thistle caterpillars ( Figure 2 ) migrated into some northwest Minnesota soybean fields this year and have been causing injury symptoms on leaves as they feed and progress through their larval stages towards pupation. Figure 1. Green cloverworm larva on a soybean leaf. Notice that the larva has three pairs of legs on its thorax (left) three pairs of pro-legs on its abdomen and one pair of pro-legs on its rear end (right). Photo: Bruce Potter, UMN Extension IPM specialist.   Figure 2 . Thistle caterpillar rolled up in a soybean leaf it uses for protection from predators while it feeds. Photo: Angie Peltier, UMN Extension While some may confuse soybean or alfalfa looper larvae for green cloverworm larvae and vice versa, there is a quick way t

  Figure 1 . Soybean plant exhibiting symptoms of Phyllosticta leaf spot and iron deficiency chlorosis. Photo: Angie Peltier   A mystery disease in northwest and west-central Minnesota soybeans. A couple of weeks ago now, unifoliate and the first trifoliate soybean leaves in research fields in Crookston and Barrett, MN (note: different varieties, different maturities) began exhibiting relatively uniform rounded brownish lesions. While not every plant had symptoms, the relative uniformity in symptoms across the field and small, brownish lesions led one to suspect an abiotic (not caused by a living organism) cause.  Fast forward a couple of weeks, and symptoms are no longer confined to unifoliate leaves or the first trifoliate leaf, but several trifoliate leaves are now showing symptoms ( Figure 1 ). Specifically, tan lesions that are bordered by larger leaf veins and ringed in a dark brown border.  While the symptoms can easily be confused with frogeye leaf spot lesions ( Figure 2 ), y