Thu Jun 30, 2011 03:28 PM CDT
Dr. Dan Talks Agronomy 06/30 15:24 Scout Late-Planted Soybeans Scout everything from stand consistency and disease to insects and weeds to save soybean bushels. By Daniel Davidson DTN Contributing Agronomist OMAHA (DTN) -- With late-planted soybeans common this year in many areas of the Midwest, now is a good time to make your first scouting assessment. First, note the current crop growth stage: emergence (VE), unifoliate (VC), 1st trifoliate (V1), 2nd trifoliate (V2), etc. Then look for large gaps in stands. While soybeans can compensate, it makes sense to mind the gap and figure out how to head off a potential problem next year. If seed drop appears consistent along rows and across the field, then the gap was probably due to something else. Did the seed germinate? Cold, wet conditions are the primary causes of seed death during imbibition, which is when the seed absorbs water to initiate germination. Did the seed rot? Seed fungicides protect the seed and seedlings for about 30 to 40 days after planting, but can be overwhelmed by a pathogen if prolonged soil conditions are cool and wet. Did soil crusting occur? This happens when you till the field before planting and then a heavy rain compacts the soil surface. Soybeans are especially vulnerable to crusting since the hypocotyl stem structure may not have enough strength to break through a clay crust. Second, look for signs of seedling disease. Dig up plants and look at the roots for signs of seedling blight from fusarium, pythium, phytophthora or rhizoctonia, which appear as dark discoloration of the stem. Planting in the right soil conditions and using a fungicide seed treatment goes a long way in minimizing seedling diseases and lost plants. Third, look for signs of insect feeding or early infestations of aphids. Bean leaf beetle is the most common early season insect pest. It usually infests the earliest planted fields and causes the most damage because they feed as soon as the cotyledons emerge and can nip off the growing point. Soybean aphids generally aren't an early season threat. But in its home range of the northern Corn Belt, given a season of late planting, soybean aphids can appear early. Fourth, look at the first flush of weeds. Are they grasses or broadleaf weeds? Note the pressure (density) and size. Be sure to time your post application when weeds are four inches tall. Bob Hartzler, weed scientist at Iowa State University, states that a good way to estimate early-season competition is to determine the density of weeds after soybeans emerge. "If densities are greater than 3 to 5 weeds per square foot when soybeans are at the VE stage, there is a good likelihood that the critical period will occur early and that weeds should be controlled before the soybeans reach the V2 or V3 stage. At lower densities, applications can be delayed to the V4 or V5 stage with little risk of yield loss," he added. Young, small soybeans can lose a high percentage of yield potential when the crop has to compete with weeds. Fifth, look for early telltale signs of iron chlorosis and nodulation. Iron chlorosis slows the growth of soybean seedlings. Eventually, as soil warms and dries and the roots proliferate, the crop will grow out of the symptoms. Also, check for the formation of root nodules at V2 or V3. Healthy nodules should be pinkish white on the side. Pure white or brown nodules are not active and may be dead. Daniel Davidson can be reached at (KL/CZ/AG) Copyright 2011 DTN/The Progressive Farmer, A Telvent Brand. All rights reserved.