Flooding and Ponding
As I gazed across my yard this morning, I couldn't believe the number of dandelion heads I saw popping up through the turf. Wait a minute - those are mushrooms! Torrential storms continue to sweep across large portions of Indiana and Illinois delaying the planting and replanting process well into the month of June.
Ponding of fields create problems for the corn crop that is now up and growing. Some university studies suggest that corn smaller than V6 may only survive being completely submerged under water for 2-4 days depending on the air/soil temperature. With high soil temperatures (77+ degrees) plants may not survive 24 hours. Once the water recedes, check the growing point (crown area). It will be firm and white if it is alive, or dark and soft if it is dead. Even if the corn in these ponded areas survive, it may continue to struggle all season. Seedling blight, crazy top and smut are just a few of the diseases that may invade these stressed plants. Corn roots need oxygen to maintain proper plant functions. Without oxygen (water-logged soils), plants will be weak, stunted and susceptible to other stresses and diseases.
Most likely much of the nitrogen in these areas will be lost due to denitrification or leaching. Once areas dry out, apply additional nitrogen preferably by sidedressing of NH3. Applicator shanks will also help open up the compacted soil allowing more oxygen to the roots.
Some farmers may opt to plant soybeans in place of the failed corn crop in these same fields that had atrazine applied earlier this spring. Soybeans are very sensitive to atrazine. There are no atrazine-tolerant soybean varieties. A farmer is at his own risk if he attempts to plant soybeans following an atrazine application in the same growing season. There are labs that will test for atrazine levels in the soil. For conventional tilled fields (6" sample), a residue level of 0.08 to 0.17 ppm of atrazine is considered "safe" to plant soybeans; any amount higher than 0.17 ppm could be injurious to the soybean crop. Consult your herbicide rep and chemical label for further directions.
Soybeans are a bit more tolerant of flooded conditions than corn. They can survive several days underwater if air temperatures stay below 90 degrees F. However, seedling diseases such as fusarium, pythium, and phytophthora can, and probably will, attack these stressed plants. Seed treatments, gene resistance, and the natural tolerance of the variety will offer some protection.
Hail Damage
Along with heavy rainfall, some storms also dropped large hail stones. Corn is relatively safe from hail damage in the younger growth stages as the growing point is protected below the soil surface. I recognize that freshly hailed corn fields look horrific at this young stage, but the plant does have the ability to push out new leaves and recover with little or no affect on yield. Once the growing point is above the soil line (around V6 stage), then increasing injury to the plant will occur up through the tassel stage as leaves are removed from hail or other defoliators. Consult the defoliation chart, "Estimated Percent Corn Grain Yield Loss Due to Defoliation at Various Growth Stages" in the Purdue Corn and Soybean Field Guide.
Have a dry weekend!
Dan Childs, Agronomist
