Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
I have seen several instances now where foliar fertilizers have been mixed with fungicides and insecticides and this mixture has caused considerable injury on flag leaves in wheat. The labels of the fungicides involved state that there is potential for injury when mixing with fertilizers. Each material would likely be perfectly safe if applied alone, but together, they interacted to cause the phytotoxicity (plant damage). Applicators should be cautious when mixing materials that may cause potential crop injury. Weather conditions, time of day, and plant conditions can all have an influence on whether or not injury will occur. Hot, sunny days and tender plants will increase the risk of injury. When in doubt, leave the foliar fertilizer out of fungicide/insecticide applications in small grains when applied near or at heading. Alternatively, apply the fertilizer in a separate application. It is important to note that 2/3 of the yield potential in small grain is dependent on the flag leaf and any injury will have the potential to reduce yields.