Corn Crop Considerations after Record Rainfall

Corn Crop Considerations after Record Rainfall

by Daniel Hudson, Agronomist, UVM Extension

Every year offers particular challenges to corn growers.  In much of New England, the challenges of the 2011 planting season are tied to excessive precipitation; some areas received seven inches of rain in less than 36 hours!  Here are a few questions that farmers have in these circumstances, followed by brief answers.

1. How long can corn seed or seedlings be under water and still survive?

Seedlings need oxygen, but they can survive for a short period of time under water.  Exactly how long they can survive is somewhat temperature dependent.  The rates of the chemical reactions happening in plants are heavily influenced by temperature: the warmer it is, the faster the reactions are happening.  In general, the faster the chemical reactions, the higher the demand for oxygen, especially in the root zone.  Plants that are under water have very little access to oxygen, and whatever oxygen is there is quickly depleted.  Thus, it is not surprising that plants cannot tolerate being submerged for nearly as long in warm weather as they can in cooler weather.  During warm weather (above 77 ⁰F) corn seedlings younger than the six-leaf stage can die after 24 hours of being submerged.  If it is cool, they can survive for up to four days.  If the seeds are just germinating, the same principle applies, but the amount of time they can survive is not as precisely known, and it can vary with variety.  If you want to know whether your seedlings have survived or if they are “dead on their feet,” dig up some seedlings and cut lengthwise through the seedling and look at the growing point (which remains on the underground portion of the plant until the five- or six-leaf stage).  If it is brown or tan and mushy, the seedling is as good as dead.  The same applies to newly germinating seed.  A healthy germinating seed will have a firm cream-colored root and shoot.


Elmore, R. and L. Abendroth. 2007.   Corn Survival in Flooded or Saturated Fields. Iowa State University Extension.  Online:

2. What is the best way to decide whether to replant a field due to damage from hail or flooding?

This is an excellent question, but the answer is longer than I have space for here.  Instead, I will refer you to the article Corn Replant / Late-Plant Decisions in Wisconsin by University of Wisconsin agronomist Joe Lauer.   Granted, Wisconsin has a different environment than New England, but it is a northern tier state that shares many similarities with our climate, and many of the same challenges.  I know that it is late in the growing season, but my general observation is that it is very tempting for farmers to replant partially damaged stands, even in cases where it is not economically beneficial, so readingthe article referenced above might be a very profitable use of time.

3. My corn was 3” tall when the hail came, and the tops are basically gone on many of the plants.  Should I replant?

Corn at this stage can easily recover from complete defoliation.  The growing point (where the leaves and ear of the plant initiate their growth) of a corn seedling remains below the ground until the plant has five or six leaves with collars.  Replanting fields that were defoliated prior to that stage is not profitable unless there are some other unusual factors.

Those with concerns about hail damage and questions about replanting can also find excellent information in the article Growing Points of Interest by Purdue agronomist Bob Nielsen.

4. We got seven inches of rain in 36 hours. How much nitrogen did I lose?

Soils have been warm enough that much of the ammonium (NH4+) has already converted to nitrate (NO3).  Nitrate moves with water, regardless of whether it is from manure, or synthetic fertilizer. In sandy soils, one inch of rain can move nitrate six inches downward! One comforting fact in much of the affected area is that the rain came down so heavily that most of it left the fields flowing over the surface rather than moving through the soil profile.  More coarse textured soils often permit more water to move through the soil profile, depending on what is under them and on the slope of the field.  While there is some comfort in knowing that we did not lose as much nitrate from the soil as we would have if the rain came over the course of three days, it still leaves a lot open to the imagination.  If you have any question about whether you will need to sidedress more nitrogen than you planned, I strongly encourage you to take pre-sidedress nitrate tests (PSNT) from at least a couple of fields, just so you have an idea of how much nitrate is there.  These tests are not perfect, but they are much better than operating with no information whatsoever.   Information about how to take the samples and interpret the results can be found at:


Warncke, D. and C. Laboski.  2004.  Field Crop Advisory Team Alert: Nitrogen losses

due to excessive rainfall.  Michigan State University Extension.  Online:


5. Will all of this rain make my soil-applied herbicides ineffective or cause injury to my corn?

It is possible that with some products, the excessive rains we received could reduce efficacy or cause some injury.  Included among these products are Prowl, Prowl H2O, and Pendimax, where injury is more likely on sandier soils.  Basis, Resolve, and no doubt other herbicides can also cause some crop damage and/or have reduced weed control efficacy in saturated soils.  Check product labels for conditions under which herbicide injury or reduced efficacy may occur.

6. Should I re-apply my soil-applied herbicides?

Even if the corn still is not emerged or if you need to replant, the answer is not to re-apply more of the same product.  Just to be clear, the reasons for this are not environmental, but due to the fact that much of the product is probably still present and higher rates could injure your crop.  In many cases, weed control will still be excellent.  The best thing to do in this case is to wait and control weeds that appear later with cultivation and/or post-emergence herbicide applications, which means it will be necessary to scout fields of concern for weed issues.

If you do replant acres to which products such as Prowl or Pendimax were applied, do not re-till the soil.  In this case, try to disturb the soil as little as possible during the planting process, and try to plant the corn two inches deep (or even a bit deeper) to get it below the herbicide in surface soil in order to avoid crop injury.  Given how much rain some areas received, even if this is done, it seems to me that there is some risk of crop injury due to the herbicide moving down further in the soil than it usually would.

References (for questions 5 and 6):

Kells, J. 2004.  Field Crop Advisory Team Alert: Excessive rain and soil-applied corn herbicides.  Michigan State University Extension.  Online:

Schirmacher, K., and J. Kells, 2004.  Field Crop Advisory Team Alert: Herbicide considerations when replanting flooded corn.  Michigan State University Extension.  Online:


Many farmers are way behind where they would like to be, relative to planting and haylage harvest.  Being tired, frustrated, discouraged, and/or in a hurry generally increases the risk for farming-related injuries.  Keep perspective, and be safe!

If you do have particular questions or concerns about your crops and would like an objective opinion, do not hesitate to contact me or your local extension agronomist.

Daniel Hudson can be reached at or by calling 802-535-7922.

It is not the intention of the author or University of Vermont Extension to endorse or promote the use of any product over another.


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