Cropping Issues in Northwest Minnesota

One of my favorite times of the year is when I get to spend some 'quality time' in northwest Minnesota corn fields looking for European corn borer injury and checking stalk strength. Corn harvest will be delayed with the rainy weather. As you are waiting for soil to dry a bit before resuming harvest, time spent checking stalk strength will be time well spent. Kernels demand sugars. Developing corn kernels place a very high demand on the plant for sugars. Stress reduces the rate of photosynthesis, thereby reducing the amount of sugars that the plant is able to produce. Many different stresses can reduce the rate of photosynthesis: too much or too little moisture, nutrient imbalances, plant injury (ex.: hail, insects, diseases), excessive plant populations, and even long-periods of cloudy weather. In northwest Minnesota in 2023 these stresses from May 1 through September 15 included average daily high temperatures 2 to 4 degrees warmer than normal ( Figure 1 ), average

A survey trip last week of soybean fields in Red Lake, Pennington, Marshall, Roseau and Kittson Counties found the soybean tentiform leafminer (STL), a pest that until recently was only known to feed on two native plants in the same plant family as soybean, American hog peanut and slickseed fuzzybean. The survey trip focused on examining soybeans growing near trees as it is thought that this may be where STL survives the winter.  Figure 1. The bottom of a soybean leaf with soybean tentiform leafminer mines on one leaflet.   While STL was found in Crookston at the Northwest Research & Outreach Center several weeks ago, during last week's survey, mines of STL ( Figure 1 ) were found not in soybeans growing near trees in field windbreaks or shelter belts, but rather only in two soybean fields that were immediately (within 5 feet or less) adjacent to larger wooded areas. Figure 2 shows what the top side of the leaf mines in Figure 1 look like; this did have the 'tented' o

Figure 1. Linear stem lesion and girdling of the stem, characteristic of Phytophthora stem rot. Photo courtesy of A. E. Dorrance; Reproduced, by permission, from Hartman, G. L., et al., eds. 2015. Compendium of Soybean Diseases and Pests. 5th ed. American Phytopathological Society, St. Paul, MN. Phytophthora root and stem rot In the last couple of weeks, I have visited a couple of soybean fields in northwest Minnesota in the Red River Valley that were suffering from Phytophthora root and stem rot (PRR). This particular disease is caused by a soil-borne, fungus-like organism ( Phytophthora sojae, Ps ) called an oomycete, that produces spores that swim in the soil toward soybean roots. The disease is favored by compacted, poorly drained and saturated soils, rain and warm temperatures.  PRR can occur as soon as the crop is planted, resulting in rotted seeds or seedlings. Other plants that are infected by Ps don't exhibit severe symptoms until later in the growing season. Symptoms char

Figure 1. Two-spotted spider mites (red arrows) and eggs (blue arrows) on a soybean leaf. Note the 'stippling' injury symptoms on the leaf which result when a spider mite sucks the green contents out of individual cells when feeding. Stippled cells will no longer contribute to the plant's growth and development. Photo: Angie Peltier, UMN Extension Spider mites Two-spotted spider mites ( Figure 1 ) are currently being observed in some northwest Minnesota soybean fields that missed some of this summer's rains and are suffering from water stress. This is because the vegetation on field edges on which the spider mites begin the growing season feeding, decreases in quality as the summer progressed and dry conditions set up. Initial spider mite infestations in soybean fields begin on field edges.