When to Stop Irrigating Corn: A Practical Late‑Season Irrigation Guide

Dimitrios Pavlou and Anna Orfanou, LSU AgCenter Scientists

As corn approaches the end of grain fill, irrigation decisions become more about precision than volume. The crop’s water use declines sharply late in the season but stopping irrigation too early can still reduce kernel weight and final yield. The key to making confident termination decisions is understanding how grain fill progresses and how soil moisture interacts with late‑season weather.

Corn continues to accumulate dry matter through the milk and dough stages, even when the crop appears mature from a distance. Many fields reach dent earlier than growers expect, but dent alone is not the only indicator for irrigation shutdown. What matters is the milk line. To evaluate the milk line, break an ear in half and look at the cross‑section of the kernels (Figure 1). The milk line appears as a clear boundary between the hard, starchy portion at the top of the kernel and the softer, doughy portion near the base. If the line is difficult to see, gently press the kernel with your fingernail starting near the base and move upward until you feel the transition from soft to firm. This quick check gives you a reliable sense of how far grain fill has progressed. As the milk line moves downward, the crop steadily approaches physiological maturity.

Figure 1. Milk line stage of corn, used to assess remaining water needs and guide final irrigation decisions before physiological maturity.

Irrigation termination timeline

You can use the milk‑line position to estimate remaining water needs:

R5 – Early Dent (Milk Line at Top): Continue irrigation. Grain filling is still active.

R5 – Mid Dent (Milk Line at ½): Likely continue irrigation. Evaluate soil moisture carefully.

R5 – Late Dent (Milk Line at ¾): Consider terminating irrigation if soil moisture is adequate.

R6 – Black Layer (No Milk Line): Terminate irrigation. Kernel weight is set.

This timeline applies broadly across corn‑producing regions. Soil type influences how long moisture lasts, but the stages themselves are universal. Heavier silt loam and clay loam soils often retain enough moisture to terminate irrigation earlier, while lighter soil may require irrigation slightly longer. Weather also plays a major role, a stretch of hot, dry days can quickly deplete soil moisture, even late in the season, whereas timely rainfall may naturally carry the crop to maturity.

As these factors converge, avoid irrigating past physiological maturity. Once black layer forms, additional water does not increase kernel weight and may complicate harvest timing or increase lodging risk.

In summary, irrigation termination should be guided by milk line progression, soil moisture, and expected weather, not by dent alone. Paying attention to these factors ensures that the crop receives the water it needs during the final stages of grain fill and unnecessary irrigation is avoided once the crop has reached maturity.

Soybean Harvest Aid Best Practices

David Moseley, Daniel Stephenson, Donnie Miller, Stephen Ippolito, and James Villegas, LSU AgCenter Scientists

In Louisiana, using a harvest-aid is common for soybean growers to improve the efficiency of their harvest. However, there are a few critical points to consider before and during application:

• Read the label: Always follow the specific instructions and guidelines on the herbicide label.
• Timing is key: Applying a desiccant before the plant reaches the R6.5 growth stage can lead to smaller seeds. This stage is identifiable when the pod's inner membrane has separated from the soybean seed (figure 1).
• Pest management: Harvest aid applications can also assist with the desiccation of troublesome late-season weeds, helping improve harvest efficiency when applied according to label requirements. Red-banded stink bugs can continue to be a threat to the crop until harvest. Continue to scout for them and apply control measures if their numbers reach the action threshold.

Figure 1. A sequence of soybean pods moving from beginning pod to maturity. The second pod with red arrows represents the R6.5 growth stage which is a key growth stage where the inner pod membrane has fully separated from the soybean seed. At the R6.5 growth stage, the seed is no longer accumulating dry matter.

Table 1 shows the preharvest or harvest aid products listed in the 2026 Louisiana Suggested Chemical Weed Management Guide for Agronomic Crops.

Table 1: Preharvest or harvest aid products labeled for soybean

For more information, you can refer to the LSU AgCenter factsheet on Desiccating Soybean.

Harvest Aids for Corn and Grain Sorghum

Stephen Ippolito, Donnie Miller, and Shelly Pate Kerns, LSU AgCenter Scientists

We are quickly approaching corn and grain sorghum harvest dates. Harvest aids can help to desiccate weeds and crop material, thereby increasing harvest efficiency; however, harvest aids do not directly reduce the moisture content of the grain. There are a number of products available for use as harvest aids for corn and sorghum; however, it is important that they are not applied prior to the crop reaching physiological maturity (black layer). It is also important to ensure that you achieve adequate spray coverage of the vegetation.

For corn, black layer (30 to 35% grain moisture) usually occurs about two to three weeks after the kernel dents. When scouting to determine if corn has reached black layer it is important to remember that kernels near the tip of the ear develop black layer earlier than kernels near the base of the ear. Applying a harvest aid prior to black layer or when grain moisture content is greater than 35% may damage the grain. Similarly grain sorghum kernels at the top of the seed head will mature (25 to 35% grain moisture) before those at the bottom. If a harvest aid is applied prior to the grain reaching 30% or less moisture the grain may be damaged. Multiple samples should be collected to ensure that the grain has reached black layer and the specific moisture content required prior to application with a harvest aid.

Below are products labeled for use as harvest aids in Louisiana. Note that sodium chlorate, carfentrazone, and glyphosate are labeled for this use in corn and grain sorghum; however, paraquat is NOT labeled as a harvest aid in grain sorghum. Always read labels thoroughly prior to use for additional precautions and application guidelines to ensure maximum effectiveness.

Severe Weather and Corn Harvest Considerations

Shelly Kerns, LSU AgCenter Corn Specialist

With tropical storm Bertha expected to impact weather conditions this week, this is a timely refresher on how severe weather can impact corn harvest. Although the majority of the corn growing regions in Louisiana are not anticipated to be severely impacted, rain and severe gusts of wind may extend northward with the potential to affect the integrity of mature/maturing corn plants.

Current Corn Status

Some of the earliest planted acres of corn (that survived the March 17th freeze) have reached black layer and are very close to being ready to cut. Replanted acres, and all other acres planted after the freeze, are following close behind. One trend that has been observed in corn planted prior to the freeze is low ear placement. This low ear placement is a physiological response to early freeze stress.

Rainfall events throughout the season were generally good for vegetative growth of corn. However, on heavier soils, nutrient leaching became an issue because soils were constantly saturated. Multiple rainfall events were expected to lead to increased disease pressure. However, disease pressure remained moderate overall. Those fields planted with disease susceptible hybrids, and those fields that were planted in continuous corn seemed to have the heaviest presence of foliar diseases. With how moist and warm this season has been, ear rots have been observed in multiple hybrids in several parishes, these ear rots may lead to docking fees at local elevators due to physical damage of the kernel and/or mycotoxin development. In addition to the freeze, an estimated 32,602 acres of corn was impacted by tropical storm Arthur. Those acres that were impacted, and are still standing, face a potential water contamination issue which may lead to more potential ear rot and mycotoxin development.

Harvest Considerations-Severe Weather and Stressed Corn

Begin Harvesting Quickly

If corn has reached maturity and has become lodged as result of severe weather, begin harvesting quickly. Lodging can negatively impact harvest efficiency, often taking 5x longer to harvest. Not only can lodged plants make harvesting physically more difficult, the drying rate of the field will also decrease as aeration becomes an issue. Additionally, kernels on ears that contact the ground will begin to deteriorate in quality.

Adjust Combine Operation

Combining speeds in lodged corn should be greatly reduced in order to pick up as many ears as possible. Additionally, the combine should be driven in the opposite direction of whatever direction the stalks are laying. As a last resort in fields with severe lodging (nearly all corn is bent over completely or very near the ground), growers may want to consider using a soybean header to salvage what a traditional corn header may not be able to pick up.

Consideration for Storing Grain

As mentioned above, ear rots are already prevalent in Louisiana. Those ears on lodged corn that have prolonged contact with the ground could exacerbate these ear rots and lead to further colonization opportunities. For those growers planning to store grain, dry affected grain quickly. Even if you notice only a small percentage of ear rots/fungal growth in the grain you are planning to store. By drying the grain quickly, you are mitigating any further fungal growth and mycotoxin development. Do keep in mind, this drying process will not eliminate or reduce existing mycotoxin levels and/or kernel damage. If storing just over the winter, 15-15.5% moisture would be adequate. However, for longer term storage, which would extend into the hotter months of the year, it is recommended to dry down grain to less than 13% moisture. The later option may be best for early harvested corn in Louisiana, which will enter storage when outside temperatures remain high.

For any further questions regarding general corn harvest considerations or adverse conditions during harvest please contact Shelly Kerns at 731-592-2944 or skerns@agcenter.lsu.edu

Update on Flood Damage in Soybean from Tropical Storm Arthur

David Moseley and Boyd Padgett, LSU AgCenter Scientists

Tropical Storm Arthur brought historic rainfall to portions of Louisiana, with some areas reportedly receiving up to 30 inches of rain in a single day. The resulting flooding and prolonged saturated soil conditions caused widespread damage to soybean fields across the central Louisiana region. Preliminary estimates indicate that approximately 114,000 soybean acres were affected, including nearly 38,000 acres with complete crop loss. An additional 15,000 acres were prevented from being planted due to excessive rainfall and persistently wet field conditions. Many remaining fields suffered partial losses that may reduce yields below levels needed to cover production costs. Overall, the total economic loss to Louisiana soybean production is currently projected to be approximately $33 million. Following the flooding, many soybean fields developed extensive yellowing (chlorosis) and dead leaf tissue (necrosis), leading to concerns about disease outbreaks. However, much of this injury is more consistent with flood-related stress than with a primary foliar disease.

When soils remain saturated for several days, oxygen levels in the root zone decline rapidly, impairing respiration and limiting the plant’s ability to absorb water and nutrients. As root function deteriorates, plants commonly develop chlorosis, nutrient deficiency symptoms, and eventually necrosis as leaf tissue dies. In addition, the hot and sunny weather that followed the storm likely intensified plant stress. Flood-damaged root systems often cannot absorb enough water to meet plant demand, reducing the plant’s ability to cool leaves through transpiration. As a result, leaves may become more susceptible to heat and solar injury, resulting in a scorched appearance and additional necrosis. Unlike most foliar diseases, which typically produce distinct lesions or recognizable disease patterns, flood injury often appears as generalized yellowing and tissue death across large portions of plants and entire areas of a field, particularly in low-lying sections where water remained the longest. Although disease organisms may later colonize stressed or dying tissue, the symptoms observed in many Louisiana soybean fields following Tropical Storm Arthur are likely the direct result of oxygen deprivation, root injury, reduced nutrient uptake, and subsequent heat and solar stress associated with prolonged flooding rather than a primary disease outbreak.

Figure 1. (Left) Mr. Tommy Laborde shows how high the water was above the soybean plants. (Right) Corn cobs were found on the top of the soybean canopy.

Figure 2. Partial soybean damage was seen across entire fields with complete plant death in the lower lying areas.

Figure 3. Yellowing (Chlorosis) and leaf tissue death (necrosis) were seen on all plants across entire fields.

Figure 4. Chlorosis and necrosis symptoms on individual leaves.

Figure 5. Differences in flood tolerance were seen across varieties.

LSU AgCenter Specialists