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Think you need to replant corn?

Corn planted early this spring faced something of a tough go getting started because of cool, wet weather that lasted a lot longer than normal. And since then, storms have raked through parts of corn country, leaving hail or wind damage. If you've got corn in either category, you may be facing a dilemma of whether or not to replant. And, this year, that's an even tougher decision to make because of the shortened window of decent planting conditions.

Start with a stand evaluation, through which you can find out both the stand you have remaining and whether or not that stand's been injured to the point of lower yield potential.

"To determine a plant stand for row crops, take several sample counts to represent the field or area under consideration. For ease of calculation, a sample size of 1/1000 acre is recommended. Measure off the distance appropriate for your row width, count the number of live plants, and multiply by 1,000 to obtain a reasonable estimate of plants/acre," according to a report from DuPont Pioneer. "Stand counts should be taken randomly across the entire area of the field being considered for replant; this may include the entire field or a limited area where damage occurred. The accuracy of your stand estimate will improve with the number of locations sampled within the damaged area."

Once you've taken a stand assessment, there are a couple of key things to consider for the stand you do have: First, what's the health of the remaining plants? How about the uniformity of those plants?

"Plants that survive but are severely injured or defoliated will have reduced photosynthetic capability and a lower yield potential," according to Pioneer. "Consider whether surviving plants are evenly distributed in the field or if the stand is uneven, with frequent long gaps in the rows. An uneven stand will yield less than a relatively even stand with the same number of plants."

Now, take that information and compare it with optimal planting dates for your area, when you planted, and what percentage of full yield potential remains in your crop based solely on those variables. Compare that with the results from what you gleaned from a stand assessment about your existing yield potential. Then, don't forget other variables to consider before you finally decide whether or not to replant.

"Even if replanting will increase yield, the yield increase must be sufficient to pay for all of the costs associated with replant such as: Extra herbicide or tillage costs (fuel, labor, equipment) to remove the old stand and prepare the new seedbed; planting costs (fuel, labor, seed, equipment); and increased grain drying costs," according to a Pioneer report. "Also consider these factors when making a replant decision: Probability of an autumn freeze prior to physiological maturity of replanted corn; and increased susceptibility of late-planted corn to summer drought or disease and insect pests such as gray leaf spot and European corn borer."

Emergence issues, too

What if your crop's not even up yet? There's still a lot of corn that was planted before the weather improved that may be struggling to break through. The same could be true of corn planted more recently that's in an area where conditions have again turned cool and damp.

The first step is finding out what you've got in the field. Is the seed still even there? If so, consider the following, says Ohio State University Extension corn production specialist Peter Thomison:

  • Coleoptile (shoot): It could be unfurled or leafing out underground, he says. "Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool and wet conditions, combinations of several of these factors, or it may be due to extended cool and wet conditions alone."

  • Poor radicle (root) development: "Dark, discolored roots and crowns, instead of a healthy creamish-white appearance, are typical symptoms of seedling diseases problems," Thomison says. "So, it is best to check these seedlings very closely for dark brown or soft areas on seedling roots and shoots. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet."

  • Seed swelling: "Often from poor seed-to-soil contact or shallow planting, seed swelled then dried out," he says. "Check seed furrow closure in no-till. Seed may also not be viable."

  • Herbicide damage: "Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants."

  • Uneven/poor emergence: "Uneven emergence may be due to soil moisture and temperature variability within the seed zone. Poor seed-to-soil contact caused by cloddy soils. Soil crusting. Shallow planting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species," Thomison says.

  • Production practices: "At times [patterns of poor emergence] are associated with a particular row, spray width, hybrid, field, or residue that may provide some additional clues to the cause," he adds. "Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing."

Even if you detect any of these issues in your fields, don't get in too big a hurry, as sometimes it can take seed up to a month to emerge in less-than-ideal conditions. Just know at what point you should draw the line between holding out in hopes that emergence will improve and deciding to replant your crop.

"Don’t forget that corn may take up to three to four weeks to emerge when soil conditions are not favorable," Thomison says. "As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential is often reduced."

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