There has been growing concern over uneven emergence during the last few days.
1) Will we see yield loss from uneven emergence? There is a possibility that uneven emergence could result in a few to several bushels of yield loss. We would stress the word “could”, and we would also note that does not mean that a field should be scrapped. Stand reduction (at least three percent and often more) should trigger replants – and we honestly do not believe that uneven emergence is always going to translate into stand reduction at this point.
2) While there is a benefit to digging up slow emerging seeds in the most serious portions of the field, we would recommend that you walk a diagonal pattern path through the field – stopping every 75 steps. At the 75the step, stop – dig up ten seeds/seedlings and take some notes on what you see. If the coleoptile sheath (the part pushing to the soil surface), looks pretty healthy (solid, plump, not soft or discolored), then it is probably just a matter of time before it pushes through (so long as we are not dealing with crusting). Even if the coleoptile sheath is just beginning to emerge from the seed (while other plants have emerged) – we are still in great shape for seedling to emerge and for the stand to even out. Potential issues that should be counted as stand reduction would be soft brown rots or brown discoloration of the radical (emerging root) or coleoptile sheath. Keep a tally of what you see and use that to estimate stand. Burrus provides an easy to use replant chart in their 2014 Growing “pocket” Guide on page 18. This replant chart can also be found at the Burrus website, (www.burrusseed.com), by choosing the Resources tab, then clicking on Reference Materials, and clicking on “Should I replant my corn?"
3) We suspect that the underlying issue is cold temperatures. We hit frigid soil conditions late last week (40s in some cases). Those temperatures brought plant development to a screeching halt. Subtle differences in plant development (differences that would have been masked given warm temps), appear dramatically in such conditions. We also think there were some underlying issues revolving around cold imbibition. Drawing cold water into the seed can cause all sorts of issues within the plant. In a few cases, we have noticed that the coleoptile sheath appears to be opening slightly while the plant is below the soil surface. This would indicate that plant growth regulators (PGRs) are getting out of whack (the sheath should open at the soil surface to release leaf tissue – not below ground). PGRs going out of whack is consistent with what we often see when the plant draws in cold water. Does that imply some damage, yes – do we think that will result in severe, stand-reducing damage – no. The underlying issue really appears to be cold temps in the majority of cases and that problem could be corrected this week.
Issues dealing with cold injury and cold imbibition were addressed in the following:
(Matt Montgomery and Stephanie Porter)