Last week I received several reports of abnormal corn emergence. Often the problems were associated with corn seedlings leafing out underground and it’s likely weather and seedbed conditions were responsible for the occurrence of the abnormal growth. Seedlings exhibiting abnormal emergence may have a twisted appearance because internal leaves start expanding before the seeding has elongated. “Corkscrewed” mesocotyl/coleoptile development may occur when the coleoptile encounters resistance (like soil crusting or a dense soil surface) as the mesocotyl elongates. Several factors (or combination of factors) may be responsible for this abnormal growth. These factors may be characterized as environmental, chemical, or mechanical. Environmental conditions associated with underground leafing include light penetration, cold soils, or heavy rains soon after planting. When plants unfurl below the soil surface, they usually turn yellow and die.
In a cloddy field where soil coverage of seed is poor and irregular, sunlight can reach the germinating seedling and induce leaf emergence beneath the soil surface. Also, heavy rains after planting can cause a hard crust, which makes emergence of small seedlings very difficult (this seemed to be the most likely factor causing problems this year). As a result, bending and twisting of the seedling below the crusted layer often occurs. Planting the seed too deep has also been associated with premature unfurling of the corn.
Certain herbicides, such as cell growth inhibitors like acetochlor, and various premixes that contain their active ingredients can show similar symptoms (i.e. twisting, abnormal growth) when excessive rates are applied pre-emergence. Besides excessive rates, improperly closed seed furrows can allow the pre-emergence herbicide to come in direct contact with the seed.
In a 2015 article concerning corn emergence problems (URL: http://www.kingcorn.org/news/timeless/CorkScrews.html), Dr. Bob Nielsen at Purdue University notes that cold soils and/or wide fluctuations in soil temperatures throughout the day during the emergence process may be a major contributing factor for the development of corkscrewed mesocotyl. In recent weeks, we have also encountered some swings in soil temperatures during emergence in areas where problems occurred.
Corn seedlings that exhibit abnormal unfurling symptoms during emergence will be unable to penetrate any but the loosest soil even if the crust is broken mechanically or softened by rain. Prompt treatment with a rotary hoe, weeder, spiketooth harrow or cultipacker may help break the crust and improve emergence. However, even when used carefully, these salvage operations can cause some damage to seedlings, which are emerging normally. To minimize poor seedling emergence due to unfurling below the soil surface, watch for cloddy seedbeds, open seed furrows, and crusting surface soils after rains.