Agronomy Blog

Western Iowa and Northwest Missouri Crop Progress

by Greg Peters | Jul 10, 2017

The recent drought monitor map tells the story in western Iowa and northwest Missouri.  Dry weather has been an issue all spring while the areas that were classified as a moderate drought  early are now considered normal after recent high rainfall events and areas that were considered normal through May have moved into the abnormally dry category to moderate drought category.  A new map comes out today from the University of Nebraska and the dry areas are expected to grow and the growth will continue as a high pressure ridge is forecast to limit rainfall into the extended forecast with temperatures into mid to 90’s.  This forecast is concerning as the corn crop is in the V12 to early blister stage, depending on the area and planting date, and is moving into a high moisture demand period of .3 to .4 inches per day.  

If the corn plants are showing stress throughout the day, the potential yield loss can range from 3 percent per day at V12, 7 to 8 percent per day at tassel and 4 to 6 percent per day in the early reproductive stages after pollination through the dough stage.  The yield loss at pollination is high because the silks are primarily water and dry conditions affect their growth for pollination.  The other factor is that pollen shed is hastened and complete pollen shed can occur in a few days vs up to 2 weeks when high yields are achieved.  We are seeing sporadic areas for tasseling in the fields from the effects of the cold, wet spring.  One positive from this uneven growth is that it will allow for pollen to be present in the field for a longer period of time to help with pollination. 

Soybeans are not considered to be at a critical stage yet as long as the plant shows recovery at night although their moisture demand is high right now at approximately .26 inches per day.  The soybeans are anywhere from V5 to the R2.  Although we like to maintain as many flowers as we can, it seems that August is the most important month for soybean yields as well as rainfall. 

Despite the overall dryness the crops in general look good for all the challenges that they have encountered this season.  Some concern has been expressed at the plant height of both corn and soybeans.  As long as the plant looks normal, except for the height, there is no correlation between height and yield.  The height reduction was caused by several factors.  The cool, wet weather in general resulted in shortened internodes along with seedling disease and slow root development from the excessive temperatures in June drying the seed furrows out.  Soybeans have been slow to grow as well with many questioning if 30 inch rows will close.  Compacted soils from wet planting have slowed down their growth along with seedling disease.   We have been seeing more Rhizoctonia than I have seen in several years.  Seed treatments have come a long way in helping reduce Rhizoctonia but the time of protection is limited.  The increase use of pre-plant herbicides will potentially lead to an increase to this pathogen in stressful environments.  Low areas and areas that we consider IDC soils have shown more yellow flash and in most cases Rhizoctonia has been the primary issue.  Cultivation can help reduce the effects from Rhizoctonia by promoting new root growth from auxiliary buds at the base of the plant.   

Producers will need to scout fields for insects that become more of an issue in dry weather.  In corn, insects such as Japanese Beetles and Adult Corn Rootworms or any insect that will reduce silk emergence will need to be scouted for.  There need to be at least a half inch of silk at the tip of the ear to successfully pollinate.  Soybeans will need to be scouted for defoliators that this year including: Thistle caterpillars, Japanese Beetles, Grasshoppers,  and Bean Leaf Beetles to mention a few.  Spider mites  and Soybean Aphids may become an issue as well and if producers spray insecticides (pyrethroids) with fungicides these fields will need to be monitored because of the loss of beneficial insects. 

I hope by the time of the next writing that I am writing about the benefits from all the rain that has fallen across our area.    


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