Links to these articles are strongly encouraged. Articles may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If articles are used in any other manner, permission from the author is required.
Drought conditions during most of the growing season in Iowa can have a profound impact on soil heath, just as when we have extreme wet conditions. The effect of drought can be noticed very clearly on crop performance when the lack of water availability is severe. This water stress can affect soil chemical, physical, and biological activities that are essential for plant and soil health.
It’s that time of year when corn yield estimations increase. The USDA NASS objective yield survey came out on August 17. This report indicates the third highest yield on record (behind 2016 and 2015) at 188 bushels per acre. Moderate to severe drought conditions are undoubtedly the cause for the reduced yields in Iowa this year. It should be expected that there will be large variation in yield within fields but also from one field to the next depending on hybrid selection, date of planting, and field uniformity.
Dry conditions this summer in some parts of Iowa will result in low and variable crop yield. Low or variable crop growth and yield significantly affect phosphorus (P) and potassium (K) uptake and removal with harvest. If dry conditions continue into the fall soil sampling season soil-test P, K, and pH results also may be affected complicating test interpretations.
A farmer in Osceola County recently found a single Palmer amaranth in a soybean field. He removed and burned the offending plant. This brings the ‘official’ ISU count of infested counties to 50. As we’ve stressed before, Palmer amaranth is likely in many more counties than reported to us.
As of July 20, the Iowa Department of Agriculture and Land Stewardship (IDALS) had received 142 cases of pesticide misuse, historically this number has ranged from 58-85 at this time of year. Dicamba was involved in 46 of these cases. Two of the dicamba cases involved use in non-crop areas, 10 involved applications on corn and 36 were related to applications to dicamba-resistant soybean (Xtend). The soybean cases were nearly evenly split between Xtendimax w/VGT and Engenia, there were no reports involving products not registered for use on soybean. Cases a
A few places in southern and northwestern Iowa have already reported twospotted spider mite populations with prolonged feeding in soybean this year. I recommend scouting corn and soybean fields for mite infestations because they thrive in hot and dry conditions. The U.S. Drought Monitor estimates about 80 percent of Iowa is abnormally dry or in a severe drought as of July 18, 2017.
Water is extremely important for crop production. When water becomes limiting to the plant it is important to understand how plants use water. We often hear the term evapotranspiration (ET) in relation to plant water demand. ET is a combination of soil water evaporation (E) and water used by the plant during transpiration (T). Soil evaporation is the major loss of water surface and typically is higher after rain and under high temperature conditions.
Dry conditions in some areas of Iowa this summer are resulting in quite variable corn growth and production potential. Some livestock producers are considering harvest of corn damaged by drought conditions for silage. Corn silage harvest results in more phosphorus (P) and potassium (K) removal than grain alone because almost the entire plant is harvested. The increased amount removed with silage differs for P and K because the relative amount of P and K is different in corn vegetative parts than in grain.
The 2017 growing season for much of Iowa so far has been characterized by low rainfall and high temperatures. This has generated concerns about water stress and yield reductions. In particular, 2017 maximum temperatures are 2-6 percent above average and precipitation 4-75 percent below average (equivalent to 0.3 to 5 inches deficit) from June 1 to July 15 (Figure 1). Radiation is 5-15 percent above average across Iowa. Minimum temperatures and growing degree days (GDD) are below average in northern parts of Iowa and above average in the central and southern parts of Iowa.
The problems experienced with off-target movement and injury in states south of Iowa, particularly Missouri, Arkansas and Tennessee have been well covered in the press, but there has been little discussion of problems in Iowa. Unfortunately, the lack of press does not mean everything has gone smoothly in the state. While I don’t know the percentage of Xtend soybean fields experiencing problems with off-target movement, in my mind the number is too high.
