I recently wrote a news release that suggested thinking about replanting might be premature because the reports I had indicated the germinating seeds had roots and shoots that were firm, but growing very slowly. While not a heat wave, the temperatures have been warmer and corn is emerging. However, some corn seeds are rotting and I think growers need to look carefully now at the situation so they can replant if necessary.
Evaluating the Stand Potential
Dig out 10 consecutive seeds and evaluate their potential to emerge. Some coleoptiles may have ruptured that lets the seedling "leaf out" under ground. Count those as dead. Seeds that are soft or roots and shoots that are soft should be counted as dead. Determine the percent of the 10 seeds that are likely to emerge and determine the potential plant stand. For example, if 8 of the 10 seeds would emerge, then the stand should be 80% of the expected stand. If the desired stand is 30,000 plants per acre, then the stand should be 80% of that, or 24,000 plants per acre. Repeat this procedure several times to evaluate the stand for the "field".
Compare Yield Potential with Replant Yield Potential
There are yield and plant population tables in MNCN61 to make this comparison. For example, planting corn May 25 gives an 86% yield potential. This yield potential is comparable to a plant stand of 21,000 plants per acre. So if the expected stand is 21,000 plants per acre or higher, replanting will not produce a better yield. If the expected stand is less than 21,000 plants per acre, then the decision is more difficult. One needs to consider the cost to replant and recognize that maturity will be later and grain will be wetter which will cost more to dry. Given those facts, I would not replant unless the stand was lower than 17,000 plants per acre.
Surface Soil Condition
There may be some surface crusting, particularly in areas that have had an intense rainfall. If plants are not up and the evaluation is that seeds are germinating and still alive, then breaking up the surface crust will help emergence. The rotary hoe is the best piece of equipment to do this. Operate the rotary hoe with a good speed and inspect the job it is doing. Rotary hoeing can be done on corn anytime from before emergence to the seedling 4-leaf stage. If corn is just about to emerge, there may be an occasional plant that is injured because a tine hits the corn shoot, but this is not serious and rarely reduces the stand. With corn that has just spiked, it is probably best to rotary hoe in the afternoon when the seedlings are less turgid and less likely to snap off.
Drags will work, but one needs to use a drag with caution because there are several different kinds of drags and they do different things. If there is a wheel track depression, dragging will move soil into the low area. This covers the plant deeper, which would not be good for these stressed plants. And if a preemergent herbicide has been applied, this soil movement may increase the herbicide rate immediately above the seed. Drags also get trash in them, which may cause damage by gouging, as the drag moves across the soil. If a drag is used, operate it for a distance at the normal speed and then inspect the job the drag is doing. Then decide if the job can be improved by adjusting the drag or parking it.