Replanting guidelines for corn

Many factors can cause unexpected stand loss or unevenness. Deciding whether or not to replant corn to achieve a desired plant population can be difficult. Before making a replant decision and incurring additional costs, it is important to evaluate the existing stand, its health, population, distribution, and yield potential versus replanting.

Evaluating Seed and Seedling Health

When corn is not germinating or emerging as it should, it is time to dig. If the seed is firm and looks healthy, it still has a good chance for germination and emergence. A water-soaked, mushy appearance indicates seed rot or decay. The same is true for the seedling. If the coleoptile (shoot), radicle (root) and seed tissue appear healthy, the seedling is in good condition.

It is important to check the stand every few days to evaluate growth. If an emerged stand is uneven or damaged, the potential for recovery and growth should be evaluated by examining the viability of the growing point. To locate the growing point, dig up a few plants, split them down the center and look for a triangular shaped structure at the point of nodal root growth, about ¾ to 1 inch below the soil surface. The growing point will remain below the soil surface until the five to six collared leaf stage (V5 to V6). A healthy growing point will have a light-coloured appearance with a firm texture. New leaves emerging every four to five days indicate normal growth. A damaged growing point will have a distinct yellow to brown, water-soaked appearance with a mushy texture.

Evaluating Stands: Plant Population and Distribution Counts

It is important to determine the plant population and distribution (uniformity) of the existing stands. Count the number of plants in 1/1000th of an acre and multiply by 1000 to obtain plant population per acre. Use the charts beside to assess population based on your row width. Take enough counts in the field to represent the existing stand, including areas that are bad and good. Sometimes, plants that are weak or questionable in growth should not be counted. Are plants evenly spaced in the row(s) or are there skips or gaps? Observe the general plant population pattern over the field. Is it low overall or just in spots? How big are the areas that are poor? The goal is to get an idea of the average stand in the field.

After plant population and health have been evaluated, yield potential of the current stand versus replanting can be determined. The table beside can be used to estimate yield potential based on your plant stand. The yield values (expressed as a percent of maximum) are based on uniform distribution of plants within the row(s), which is not always the case. If stand health is very questionable or regrowth can delay maturity, replanting may be the best option. Some hybrids can tolerate and compensate for lower stands better than others (example, hybrids with a flex ear). However, if the existing stand is lower than the adapted population range of a hybrid and calendar date is not an issue, replanting may be best.

Determine the Cause of the Poor Stand

There are many factors that can contribute to poor stands, and it is important to look at the entire field to get the “big picture”, and also to dig and closely examine individual plants to determine the cause. Some things to look for include: Weather conditions between planting and emergence, was it too cold, wet, or even too dry after planting? Are there any patterns in the field that would indicate compaction, herbicide injury, insect, or disease pressure, etc.? Check the planting depth of the corn to determine if it was planted too deep or too shallow, both of which can affect emergence. Look for any other planter related issue that may have caused stand losses.

Other Important Decision Guidelines

• Each field has a unique set of conditions and should be evaluated individually.
• Early replant decisions should be based on existing population and its potential, while later decisions are based more on calendar date and maturity.
• If replanting early, use adapted hybrids to maximize yield.
• After optimum planting dates, select earlier maturing hybrids.

When Is It Optimal to Switch Corn Maturities?

Careful thought must be taken when considering switching to an earlier corn hybrid. With delayed planting, calendar date, frost date, normal CHU accumulation/climate data, and the hybrid’s inherent ability to dry down must be considered. Delayed planting can reduce yield potential, increase moisture stress at pollination, and the timing of insect and disease pressure may influence the final yield. The urgency to jump to an earlier hybrid must be tempered. If replanting past the optimal planting window for your location, soybeans may be a better option unless herbicide(s) or other practices limit use. The table beside provides recommendations based on location in the province of Ontario (OMAFRA- Agronomy Guide for Field Crops- Switching to Shorter Season Hybrids).

Final Decision

Determine if the expected yield, cost of replanting, and risk associated with replanting the corn is more or less than the expected yield, cost, and risk associated with keeping the current stand. While the decision to replant is generally not easy, having a good average population from several stand counts of the current stand, along with the information around expected yields from keeping thin stands and the expected yields from replanting can help make that decision easier.

Speak to your local NK^® Seeds Agronomist for more information, or join the conversation online – connect with us at @NKSeedsCanada on Twitter and Facebook.

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