Replanting goes with the territory. Farm long enough and you're going to be faced with the gut wrenching decision of replanting roe laving a field alone. This year's cool, wet spell in the middle of the planting season nearly guarantees that more people than normal may face this decision this year, perhaps as early as this week.
Last week a crop insurance adjustor reported that one farmer in central Indiana had several hundred acres of soybeans that could well need replanting. Soybeans are usually able to fight through cool weather as well or better than corn, as research in the past two decades has proven, but apparently the timing was just wrong in this case. Soybeans are also typically able to compensate for thin stands, as long as the remaining stand is relatively even and weed control is in hand. But there comes a point where thin is too thin.
The Purdue University Corn & Soybean Field Guide, published by the Purdue Crop Diagnostic Training Center, contains helpful information for making decisions on both corn and soybean replant issues. Let's consider corn.
According to the table in the guide, if you planted April 30, but have 20,000 plants per acre, you can expect about 92% of top potential if the final estimated stand was 28,000 plants per acre or higher. Please note that the table is based upon final stand, not what you planted or what you see today, especially if some plants are suspect or far behind the others already. Very late emergers, especially if surrounded by plants that emerged on time, often become weeds, sapping moisture and nutrients without contributing much, if anything, to final yield.
If you were shooting for 200 bushels per acre, you could still expect 184 bushels per acre, at least in theory. In reality, you're likely to have 24,000 in some spots and 16,000 in others. Be sure to do several stand counts at random, and weigh whether the thinner spots make up a majority of minority of the field. In some fields, stands seem to be better on high ground, which wasn't as wet and cool for as long, especially in fields that are not naturally well-drained or equipped with a modern tiling system.
If you replant May 30 and obtain 28,000 plants per acre, the table indicates you can expect only 81% of original potential, based on much later planting date. That would pencil out to 162 bushels per acre.
Bottom line is that even if a corn stand isn't up to your standards, it may not pay to replant. Part of the decision may rest upon how much of the replant cost your seed company will bear. Companies vary in replant policies. If you have the type of crop insurance coverage that will pay in replant situations, be sure to contact your agent before you tear up the field.
Look for help on soybean replant decisions on our Website tomorrow.