Dry conditions causing crop stress, herbicide carryover and drift, nutrient deficiencies induced by the dry conditions, armyworms in forages, and a frost event in NE Iowa were some of the common or big issues or questions ISU Extension and Outreach Field Agronomists heard about or received this past week. Read on for more specifics about what’s happening around the state.
North Central Iowa
A common sight across the state this summer has been yellow or white patches of soybean in otherwise green fields. This ICM Blog will review several possible causes of yellow soybean and provide resources regarding each phenomenon.
Iron Deficiency Chlorosis (IDC)
Corn tassels began showing in some Iowa fields this past week and in the next week corn in most fields will be at the R1 stage (silking). Most soybean fields are at R2 or will be at the R2 to R3 growth stage soon. Nutrient concentrations vary greatly with crop growth stage and plant part sampled. Calibrations of tissue tests based on field response trials for corn and soybean in Iowa and other states have been for leaves at the R1 growth stage in corn and the R2 to R3 growth stage in soybean.
Since early August, soybean in several fields began showing typical potassium (K) deficiency symptoms on leaves located in the middle to upper canopy. This is not surprising in fields or portions of fields with soil-test values in the very low or low K soil-test interpretation categories that did not receive adequate preplant K fertilization. Potassium deficiency symptoms are well-known and very common in older leaves during early growth stages.
In-season plant tissue testing can be useful in diagnosing nutrient deficiencies in field crops, but it must be used with caution. Extra care is needed this year given the unusual crop planting and growing conditions.
