Louisiana Soybean Planting Update and Tips

David Moseley, LSU AgCenter Soybean Specialist

Topics Include:

• Projected number of soybean acres in Louisiana
• Soybean inoculation
• Other biological seed treatments
• Soybean plant populations and replanting

The United States Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) estimates Louisiana farmers will plant 1.05 million acres of soybean in 2025. This estimate is down 5% from 2024.

By March 30^th, farmers had planted 6% of the Louisiana soybean crop which is 2% more than the 5-year average, according to the USDA-NASS.

Figure 1. Soybean acres in Louisiana from 2006 – 2025 according to USDA-NASS.

Soybean Inoculation

Soybean plants, despite their high nitrogen requirement, typically don't need nitrogen fertilizer applications due to their symbiotic relationship with Bradyrhizobium japonicum bacteria. These bacteria fix atmospheric nitrogen into a plant-available form. Inoculation with Bradyrhizobium japonicum is crucial in fields with no recent soybean history. However, even in established soybean fields, research has indicated inoculation can increase yield at least slightly. Successful nodulation, and thus nitrogen fixation, can be negatively impacted by factors like extreme temperatures, soil pH imbalances, salinity, waterlogging or drought, nutrient deficiencies, and high soil nitrogen levels. To assess active nodulation, farmers should examine nodules during early vegetative growth (V1), with nitrogen fixation beginning around V2 - V3. Healthy, active nodules will exhibit a pink to red interior. If nodulation is inadequate, a corrective nitrogen application may be necessary. This information is from the fact sheet, “Soybean Inoculation and Nitrogen Fixation,” produced by the Science for Success team, a collaboration of university Extension soybean agronomists, and funded by the United Soybean Board. For specific management recommendations on soybean inoculum, refer to the Oklahoma State University article, Management of Soybean Inoculum.

Other Biological Seed Treatments

Funded by the United Soybean Board, the Science for Success team published a fact sheet, “Biological Seed Treatments on Soybean,” detailing a nationwide trial of various biostimulant seed treatments. The trial revealed no significant yield improvements. Potential reasons for this include unfavorable environmental conditions, inactive microbes within the treatments, or competition from native soil microbes. The fact sheet emphasizes that the study included only a selection of available products, and that proper handling and application are crucial. It recommends farmers collaborate with university Extension for on-farm testing of products.

Soybean Plant Population and Replanting

Soybean plants can achieve maximum yield across a range of plant populations. The LSU AgCenter's 2025 Soybean Variety Yields and Production Practices publication recommends a final stand of 78,000 to 130,000 plants per acre under normal situations. Because not all planted seeds germinate and thrive, the initial seeding rate must exceed the desired final population. Factors like cool, wet, dry, or crusted soils can hinder emergence and reduce plant productivity. For detailed information on low plant stand causes and replanting decisions, consult the recent Crop, Forage, and Turfgrass Management journal article, "Low soybean plant population: Is replanting necessary?"

Early-Season Insect Pest of Corn in Louisiana: Wireworms, Sugarcane Beetles, and Cutworms

James Villegas, LSU AgCenter Field Crop Entomologist

As corn planting is in full swing, it’s important to be aware of early-season pest based on reports from the past couple of years in Louisiana. Here are some of key pests to watch out for:

Wireworms

Wireworms, the larvae of click beetles, are slender, brown or yellowish-brown, and have rigid, cylindrical bodies with a wire-like appearance. These larvae can live in the soil for several years, feeding on plant roots and other organic matter. Depending on the species, it takes around 3 to 5 years for the larvae to mature into adult beetles. In corn, wireworms cause significant damage by feeding on the roots, leading to stunted growth and reduced yields. This damage is particularly severe in seedling corn, as wireworm feeding reduces the plant's ability to absorb water and nutrients, making them more susceptible to stress and disease. Effective management of wireworms requires long-term strategies, such as crop rotation, which can disrupt the pest's life cycle and reduce their populations over several years. Tillage can also disrupt wireworm habitats, though it may not be suitable for all farming operations, such as no-till or reduced-till systems. Producers should carefully evaluate these strategies when designing a comprehensive wireworm management plan tailored to their fields' specific conditions.

Sugarcane beetle

The sugarcane beetle is a sporadic pest affecting several crops, including corn. This beetle is common throughout the southeastern U.S. Only the adult stage of the beetle causes injury to crops. In corn, the adults feed on seedlings below the soil surface, targeting the roots or the growing point of the plant. The damage caused by the beetles includes ragged, bean-sized holes at the base of the plants. This feeding behavior often results in terminal leaves dying, leading to stunted and nonproductive plants. Individual beetles are capable of damaging multiple plants in a row and severe infestations can significantly reduce plant stands, sometimes necessitating replanting. Monitoring infested fields for stand recovery as the crop matures is advised to manage the impact of these pests. Additionally, avoiding planting corn into sod or grassy fields and using high rates of seed treatments can help minimize seedling injury when beetles arrive in the field. Foliar application is not recommended as the beetles are protected underground.

Cutworms

Cutworms are significant early-season pests of corn in the U.S. The larvae, which can grow up to 2 inches and are typically pale grey to black with a greasy texture, feed on plants at night or on overcast days and burrow into the soil during the day. Damage from smaller larvae causes “shot-hole” leaf feeding, while larger larvae can cut plants at or below soil level. Larvae may also sometimes bore into and tunnel within the stem. Mature larvae pupate in the soil. Effective management includes weed control before planting, as fields with heavy weed presence are at higher risk. Cutworms are usually problematic in reduced tillage or no-till fields that received a late burndown application, but clean fields should still be routinely scouted. Thresholds for cutworm damage in Louisiana corn are 6-8% for above-ground cutting or 2-4% for below-ground boring. Cooler weather keeps cutworms closer to the soil surface, while warmer weather drives them deeper into the soil, increasing the risk of injury to the growing point. Insecticide seed treatments and Bt technology may provide some protection, but large larvae are less susceptible. If necessary, a low label rate of a pyrethroid, such as bifenthrin, can reduce cutworm injury.

The 2025 Louisiana Field Crops Insect Pest Management Guide can be accessed using the link: https://www.lsuagcenter.com/portals/communications/publications/management_guides/insect_guide

Soil Organic Matter: Transforming Soil Physical Properties for Better Yields

Leandro O. Vieira II, LSU AgCenter Soil Fertility Specialist

Soil organic matter greatly improves soil physical properties in the soil, which includes the formation and stabilization of soil aggregates, and the improvement of soil aeration, water flow and water-holding capacity. Soil organic matter accumulation in the soil can also result in the reduction of erosion and runoff and the increase in soil temperature early in the growing season.

Soil aggregate formation and stability are likely the greatest benefits of organic matter on soil physical properties. Earthworms, insects, and microorganisms combine organic materials with mineral soil by feeding on plant residues and manure. These organisms' residue stabilizes soil aggregates by binding soil particles together. Additionally, bigger soil organisms (e.g., insects and earthworms) promote water movement and soil aeration by forming channels called soil biopores. In addition to creating tunnels, earthworms also keep them structurally sound by secreting mucus that fortifies the walls of those channels. Further increasing soil porosity, old root channels can stay open during root breakdown.

Moreover, organic matter greatly increases the soil's ability to retain water. By enhancing soil structure and total pore space, it will be able to store more water than mineral soil and indirectly affects how much water is accessible to plants (Figure 1). An extra 20,000 gallons of plant-available water may be retained in a single acre of soil by increasing soil organic matter by 1%. This will result in more spaced intervals for irrigation and, in consequence, lower expenditures due to the decreased time running water pumps. On the other hand, the loss of soil organic matter may significantly lower the soil's ability to retain water, which increases erosion, runoff and needs for irrigation.

Another advantage of better soil physical properties and the presence of organic matter covering the soil, such as plant residues, is the decrease in erosion and runoff. These organic materials have the potential to slow down water flow, improve infiltration, and reduce the effect of rainfall on the soil surface. By protecting the topsoil, the most fertile layer of the soil, this decrease in erosion and runoff can greatly boost crop yields.

Last but not least, the buildup of organic matter can cause the topsoil to darken, which is advantageous in the early growing season. Soil microbial activity, seed germination, and seedling growth can all be benefited by a warmer soil. Furthermore, organic matter may operate as a buffer against temperature fluctuations in the soil, preserving a more favorable temperature for microbial activity and crop development.

Figure 1. Each 1% of soil organic matter can hold up to 20,000 gallons of water per acre.

Early season management considerations for thrips in cotton

Dawson Kerns

Thrips are the number one pest of seedling cotton in Louisiana. Tobacco thrips are the primary species that infests cotton with western flower thrips present at lower numbers. These insects feed on cotton seedling leaves resulting in crinkling and upward cupping of leaves, stunting, and delays in maturity. Preventative treatments (ISTs and in-furrow) typically provide protection against thrips up to the second leaf stage. Supplemental foliar treatments may be required to maintain control. Treat when an average of one or more immature thrips are found per plant or when large numbers of adults are present and there are signs of damage to new leaves. Under ideal growing conditions, treatment for thrips is not recommended once cotton reaches fourth leaf stage.

Moderate thrips injury that would warrant treatment.

ThryvOn: ThryvOn is a Bt cotton trait with activity against thrips and plant bugs. The ThryvOn trait provides excellent control of thrips and should not require supplemental insecticides to manage thrips infestations. The ThryvOn trait provides protection against thrips by deterring feeding and egg-laying, therefore it is not unexpected to see adult and immature thrips on ThryvOn cotton plants, and it is not recommended to use in-furrow or foliar treatments with ThryvOn cotton for thrips management. It is important to consider that ThryvOn cotton can still show signs of thrips damage, and the addition of seed treatments, in-furrow insecticides, or foliar applications to ThryvOn cotton can visually reduce thrips damage, but the damage is only cosmetic and not economically significant. However, additional seed treatments or in-furrow insecticides may be desired for managing other early season pests.

Insecticide Seed Treatments (ISTs): ISTs are the most common method for managing thrips in cotton. Standard rates of imidacloprid seed treatments (0.375 mg ai/seed) are the minimum required for insect control in cotton. Cotton seed treated with anything less, such as the base seed treatment packages do not control thrips and will likely require supplemental foliar or in-furrow insecticides to maintain adequate thrips control. IST performance can be highly variable under adverse weather conditions that stunt seedling growth or heavy thrips infestations, and in such cases, foliar insecticide applications may be warranted.

In-furrow: In-furrow insecticides can replace or supplement ISTs for management of thrips, and in many cases are more effective than seed treatments. However, using in-furrow products requires specialized equipment, additional calibration, and more time when planting. In-furrow applications of imidacloprid at the highest labelled rate can provide good control against thrips but may still require a supplemental foliar spray. Another in-furrow option is the granular product, Aglogic 15G (aldicarb), which provides excellent control of thrips and has activity against nematodes.

Foliar sprays: Resistance monitoring to organophosphates across the mid-south has been ongoing for several years and resistant tobacco thrips populations have been found in Louisiana. This limits the effectiveness of acephate and Bidrin against thrips infestations in cotton. Currently, the recommended foliar treatment for thrips is Intrepid Edge at 3.0 fl oz/a. This product is more expensive than organophosphates but is less prone to flaring aphids or spider mites. One of its active ingredients, spinetoram, also provides better control of western flower thrips than western flower thrips. It is recommended to apply Intrepid Edge surfactant to improve efficacy (surfactants in herbicides will work if co-applied).

A few final considerations, ideally foliar applications should be made by the second leaf stage to prevent excessive damage. Under adverse weather conditions to stunt cotton growth, it may be necessary to apply foliar insecticides at later growth stages. Keep in mind that the presence of a few adult thrips is not a sign that control method is not working. In many cases, those individuals have just migrated into the field and haven’t been exposed yet. The presence of immatures is a key sign of control failure because they indicate that adults have survived and successfully reproduced. Avoid spraying on signs of plant injury alone and instead look for presence of thrips and injury to new leaves. Some damage may be non-thrips injury or old.

LSU AgCenter Specialists