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David Moseley, Price, III, Paul P, Padgett, Guy B., Kerns, Shelly, Orfanou, Anna, Pavlou, Dimitrios, Ippolito, Stephen, Miller, Donnie K., Vieira, Leandro
Anna Orfanou & Dimitrios Pavlou, LSU AgCenter Scientists
One of the most common observations during the early growing season is uneven crop growth within the same field. While some areas emerge quickly and develop vigorous canopies, others appear delayed or less uniform. These differences can be frustrating for producers, especially when planting conditions seemed favorable and management practices were applied uniformly across the field.
The reality is that crops rarely experience uniform growing conditions. Early-season variability is often the result of multiple interacting factors, including soil properties, weather conditions, field history, and management practices. Understanding these factors can help producers better diagnose problems, interpret field conditions, and make informed management decisions throughout the season.
Many differences observed during the growing season begin below the soil surface. Even within a single field, soil texture can vary. Areas with higher clay content tend to hold more water but may remain saturated longer after rainfall events. In contrast, sandy areas drain more rapidly and can dry out quickly during periods without precipitation.
These differences influence seed germination, root development, nutrient availability, and early plant growth. Following a wet spring, heavier-textured portions of a field may experience delayed emergence due to saturated conditions and reduced soil oxygen. During drier periods, lighter-textured areas may begin showing signs of moisture stress sooner than surrounding portions of the field.
Compaction can further amplify these effects. Compacted layers restrict root growth, reduce water infiltration, and limit the crop's ability to access water and nutrients later in the season. Areas with repeated equipment traffic, turn rows, or historical tillage issues often become visible as distinct patterns of crop variability.
Weather conditions during planting and emergence play a critical role in determining crop uniformity. Differences in soil moisture and temperature can create differences in emergence timing.
A crop that emerges several days later than neighboring plants may struggle to fully recover its yield potential. Early-emerging plants often gain a competitive advantage by capturing more sunlight, water, and nutrients. As a result, variability that begins during emergence frequently persists throughout the season.
Rainfall patterns can also create localized variability. A field may receive the same total rainfall, yet differences in drainage, topography, and soil characteristics determine how much water is actually available to the crop. Heavy rainfall events may lead to ponding in some areas while leaving other portions relatively unaffected.
Nutrient uptake is closely linked to both soil moisture and root development. Saturated soils can slow root growth and reduce nutrient uptake, while excessively dry soils may limit nutrient movement toward the root system. In some cases, nutrient deficiencies are not caused by insufficient fertilizer application but by environmental conditions that temporarily restrict nutrient availability.
Similarly, variability in residue distribution from previous crops can influence soil temperature, moisture retention, and nutrient cycling. Areas with heavier residue may remain cooler and wetter during early spring, affecting emergence and early-season growth.
Scouting fields early and frequently remains one of the most important tasks. Identifying patterns of variability can help determine whether issues are related to soil type, drainage, planting conditions, pest pressure, nutrient availability, or irrigation management. Comparing healthy and affected areas, checking soil moisture conditions, and reviewing recent weather patterns can help identify the primary factors contributing to variability.
Many variability patterns become easier to observe with precision agriculture tools, particularly when field symptoms are not easily visible at ground level. Precision agriculture tools, such as soil moisture sensors, drone and satellite imagery, elevation and yield maps, can help producers better understand this variability and improve management decisions over time.
Not all early-season variability leads to yield loss. Crops can often compensate for minor differences in growth, particularly when favorable weather conditions occur later in the season. However, severe or persistent variability may indicate underlying issues that need attention.
Early-season observations provide valuable information about field performance and can help guide future management decisions. Areas that consistently exhibit poor growth may benefit from additional soil sampling, drainage improvements, compaction mitigation, or adjustments to fertility and irrigation strategies.
Boyd Padgett and Trey Price, LSU AgCenter Plant Pathologists
Foliar symptoms are usually not evident until soybean is in the mid to late reproductive growth stages. Initial symptoms are small chocolate brown lesions on the petioles near the leaflet (Figure 1). As the disease progresses, foliar symptoms are expressed as a reddish brown to tan discoloration on the upper leaf surface in the upper canopy (Figure 2). Leaves have a leathery appearance. The fungus can sporulate in older lesions (resemble ashes) (Figure 3). Advanced disease stages result in premature defoliation and discolored pods, and reduced seed quality. The seed phase is evidenced by purple-stained seed (Figure 4).
Figure 1. Petiole lesion.
Figure 2. Red to brown leathery symptoms in the upper canopy.
Figure 3. Advanced symptoms (ashy upper leaf surface).
Figure 4. Purple seed stain.
Symptoms occur predominately on the leaves, but may appear on the petioles, stems, and pods (Figure 5). Initially, small chocolate brown to purplish spots form on leaflets. If the disease continues to develop, mature lesions have light brown to gray centers with a reddish brown to purplish margin. Stem lesions are rare and are elliptical with red centers and dark brown to black margins. Pod lesions are circular to elliptical, sunken, and light gray to brown.Infected seed exhibit grayish to light purple lesions.
Figure 5. Foliar symptoms of frogeye leaf spot.
Caused by the same fungus causing sheath blight in rice. Initial symptoms appear as water-soaked greasy blotches on the leaflets (usually in the lower to mid canopy) (Figure 6). As the disease progresses, adjacent leaflets adhere together by white fungal mycelium. If favorable conditions persist, the foliage becomes brown, and pods will have reddish-brown lesions. Under high severity pod abortion can occur. The disease is usually evident during the early reproductive stages of growth and later.
Figure 6. Aerial blight in lower canopy. White fungal growth (mycelium), matted leaves, and blighted leaves.
Symptoms begin in the lower canopy as small brown to tan raised pustules (volcano-like) on the lower leaf surface (Figure 7). Young spores produced in the pustules resemble sand and are tan in color. Older spores are darker in color. Mature pustules can coalesce and cause the leaflets to defoliate. Symptoms are usually evident when soybean is in the mid (R3) to late (R6) reproductive growth stages. Pustules can occur on petioles and pods when disease is severe.
Figure 7. Soybean rust raised pustules on lower leaflet surface.
A fungal disease affecting the leaves, stems, pods, seeds, hypocotyls, and roots. Foliar symptoms usually initiate in the lower canopy and appear as small reddish-brown specks. Mature lesions are round to elongate with brown centers (zonate pattern) and dull green to yellow-green halos (Figure 8). Pod lesions are usually circular with purple-brown centers and brown margins. Dark reddish-brown lesions can form on the hypocotyl, taproot, and lateral roots. These lesions turn dark violet-brown when the fungus produces spores.
Figure 8. Target spot lesion.
Caused by a bacterium and is not a major disease in Louisiana. Symptoms are very similar to soybean rust. Symptoms begin as small pale green, water-soaked spots with elevated centers on the upper and lower leaf surface. Mature lesions are dark brown with elevated volcano-like pustules on the lower leaf surface (easily confused with rust) (Figure 9). Pustules are dry in appearance. Pustules can be found on the pods in susceptible varieties.
Figure 9. Bacterial pustule.
David Moseley, LSU AgCenter Soybean Specialist
Recent rainfall and flooding have resulted in stand loss in some Louisiana soybean fields, forcing producers to consider replanting in late June. When planting is delayed beyond the optimal window, soybeans have less time to develop canopy, branch, and compensate for low plant populations. As a result, achieving an adequate final stand becomes critical, and one of the most effective management adjustments is increasing seeding rate.
Figure 1 indicates that higher seeding rates may help increase yield when planting outside the optimum window. The data in Figure 1 was collected from a population × planting date trial conducted at the LSU AgCenter Dean Lee Research and Extension Center in 2025. The results are based on a March planting date, as it was the only planting date harvested. Although this represents an early planting date, the results may still be relevant to late June conditions. In both cases, shorter daylength leads to reduced vegetative growth and earlier flowering compared to soybeans planted within the optimal window. Based on the data, lower seeding rates (50,000–100,000 plants per acre) are more likely to result in reduced yield under late planting conditions, while higher populations (200,000–250,000 plants per acre) may help improve yield.
Figure 1. Relationship between soybean planting rates (seeds/A) and soybean yield (Bu/A) for a March planting date. The data indicates yield increases with planting rate for a planting date outside of the optimum planting window.
Figures 2–4 illustrate yield response to planting date across the Northeast, Central, and Southwest regions of Louisiana. Across all regions, peak yields occur from mid-April to mid-May, followed by a steady decline as planting is delayed into June. By late June, yield potential is substantially reduced. However, these figures provide realistic expectations and reinforce the importance of management decisions that minimize losses. Increasing seeding rate in late June plantings can improve stand establishment, accelerate canopy closure, and help maximize remaining yield potential.
Figure 2. Based on the quadratic response, the optimum soybean planting date for the Northeast region is April 7. Planting either before or after this date results in reduced yield. The yield potential for a late June planting date is expected to be approximately 33% lower compared to an April 7 planting.
Figure 3. Based on quadratic responses, optimum soybean planting date windows for the Central region occur from mid-April to early-May, depending on maturity group. Planting either before or after this window resulted in reduced yield. Yield potential for a late-June planting date is expected to be approximately 40% lower compared to planting within the optimum window.
Figure 4. Based on quadratic responses, optimum soybean planting dates for the Southwest region occur from late-April to May, depending on maturity group. Planting either before or after this window results in reduced yield. Yield potential declines steadily with a June planting date, and late-June planting dates are expected to produce approximately 40% lower yields compared to planting within the optimum window.
Dimitrios Pavlou and Anna Orfanou, LSU AgCenter
Water stress is often described in simple terms, either the crop “needs water” or it does not. However, in Louisiana row crop systems, where soils vary and weather conditions can change quickly, water stress is rarely caused by a single factor. Instead, it develops through the interaction of soil properties, weather conditions, crop growth stage and field variability. Understanding these interactions is essential for making informed irrigation decisions and for explaining the variability commonly observed across fields.
Two fields may receive the same rainfall but respond differently depending on whether soils are dominated by sand, silt, or clay. Sandy soils drain quickly and hold relatively little water, meaning crops can move from adequate moisture to stress within only a few days. Clay soils retain water longer but are more prone to saturation, which can limit oxygen availability and restrict root growth. Silt loam soils often provide high productivity but can become vulnerable to compaction and surface sealing, which may restrict water infiltration and root development. As a result, rainfall totals alone do not fully determine crop water availability. Soil texture largely controls how long water remains accessible within the root zone.
Louisiana weather patterns further complicate water management decisions. Sudden heavy rainfall events, prolonged dry periods, high humidity, heat waves, and windy conditions all influence evapotranspiration, canopy development, and soil drying rates. In some situations, field conditions may shift from saturated to moisture stressed within only a few days during periods of high temperature and wind. In other situations, soils may remain saturated for extended periods following slow-moving rainfall events.
When irrigation decisions rely only on fixed schedules rather than current soil and weather conditions, the risk of both under-irrigation and over-irrigation increases.
Water stress does not affect crops equally throughout the growing season. Some growth stages are considerably more sensitive than others. Corn is particularly sensitive during the late vegetative to early reproductive stages, while soybean is more vulnerable during pod set and seed fill (R3-R6). Cotton is highly sensitive during squaring and early bloom. Even relatively short periods of moisture stress during these stages might reduce yield potential. Because of this, irrigation timing is often just as important as the total amount of water applied.
Figure 1. Leaf rolling is a common response of corn to moisture stress and high evaporative demand.
Production fields might contain multiple soil types, drainage patterns, and compaction zones. These differences create field variability in water availability and crop response. One area of the field may show signs of wilting, another may remain saturated, while another area may appear unaffected. Many of these patterns become easier to identify through frequent scouting, soil moisture monitoring, drone imagery, or yield maps. For instance, soil moisture sensors can provide information about soil moisture conditions throughout the growing season, while remote sensing imagery can show stress patterns through vegetative and water status indices.
Taking a systems approach to water stress allows growers to move beyond simple rainfall totals and toward more precise, field-specific management decisions. When soil properties, weather conditions and crop growth stage are considered together, irrigation decisions become more effective and better aligned with actual crop needs. Improving the understanding of these interactions can help increase irrigation efficiency, reduce production risk, and improve yield stability.
Leandro O. Vieira II and Shelly Kerns, LSU AgCenter Scientists
Potassium (K) is one of the three most important yield-limiting nutrients for corn. It plays a key role in activating more than 80 enzymes and helps regulate plant water relations. In other words, plants well-nourished with potassium are better able to withstand stresses such as drought and low temperatures.
Unlike nitrogen and phosphorus, potassium is not primarily bound in organic matter and is mainly associated with the mineral fraction of the soil. Aside from fertilizer applications, plant-available K is released through the weathering of soil minerals. Therefore, performing regular soil testing is essential to monitor soil pH and potassium levels and to maintain them within optimal ranges.
Corn takes up approximately 1.36 lb of K per bushel of grain produced. However, only about 0.22 lb K per bushel is removed in the grain. For example, a 150-bushel corn crop removes approximately 33 lb K per acre in grain. The remainder, which is about 77 lb K per acre is taken up into the stover (assuming 4-4.5 tons of residue per acre). This potassium will return to the soil if the residue is left in the field. Because of the large seasonal demand for K, regular soil testing is critical to prevent deficiencies.
Potassium deficiency in corn typically appears as chlorosis at the tips and margins of older leaves, progressing to ‘burning’ along the leaf margins (Figure 1). These symptoms develop first on older leaves because K is highly mobile within the plant, allowing it to be redistributed to support new growth. As deficiency becomes more severe, plants may exhibit reduced growth, poorly developed root systems, increased susceptibility to diseases, weak stalks, and greater risk of lodging.
Figure 1. Potassium deficiency in corn plants at early vegetative (left) and reproductive stages (right).
Although potassium availability is often limited by low soil pH or low soil-test K levels, another important factor is soil compaction. Compacted soils restrict root growth, reducing the volume of soil explored by roots (Figure 2). As a result, plants may experience nutrient deficiencies, particularly for nutrients with limited mobility in the soil.
In summary, ensuring adequate potassium nutrition requires regular soil testing, proper fertilization, and management practices that minimize soil compaction.
Figure 2. Corn roots in compacted soil (left) versus non-compacted soil (right). Roots in non-compacted soil are deeper and more expanded horizontally.
Stephen Ippolito and Donnie Miller, LSU AgCenter Weed Scientists
Acetyl CoA Carboxylase (ACCase) inhibitors such as clethodim, fluazifop, quizalofop, and sethoxydim are excellent herbicides for controlling troublesome grasses in soybean and cotton. Below are best practices to improve effectiveness when applying these herbicides.
Please read labels thoroughly prior to use for additional precautions and application guidelines not included in this article.
| Specialty | Crop Responsibilities | Name | Phone |
| Soybeans | Agronomic | David Moseley | 318-473-6520 |
| Wheat | Agronomic | Boyd Padgett | 318-614-4354 |
| Pathology | Cotton, grain sorghum, soybeans | Boyd Padgett | 318-614-4354 |
| Pathology | Corn, cotton, grain sorghum, soybeans, wheat | Trey Price | 318-235-9805 |
| Entomology | Corn, cotton, grain sorghum, soybeans, wheat | James Villegas |
225-266-3805 |
| Weed science | Corn, cotton, grain sorghum, soybeans | Stephen Ippolito | 318-473-6520 |
| Nematodes | Agronomic | Tristan Watson | 225-578-1464 |
| Irrigation | Corn, cotton, grain sorghum, soybeans | Stacia Davis Conger | 904-891-1103 |
| Ag economics | Cotton, feed grains, soybeans | Kurt Guidry | 225-578-3282 |
| Soil fertility | Corn, cotton, grain sorghum, soybeans | Leandro Vieira | 225-578-2110 |
| Corn, Cotton, and Grain Sorghum | Agronomic |
Shelly Pate Kerns | 318-435-2908 |
| Entomology | Field Crops | Dawson Kerns | 806-474-7220 |
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