Wheat Fertilization, Vernalization, and Freeze Damage

Boyd Padgett, LSU AgCenter Small Grain Specialist, Noah DeWitt, LSU AgCenter Wheat Breeder, Steve Harrison, LSU AgCenter Wheat Breeder

Wheat Fertilization and Vernalization: Nitrogen (N) fertilization of wheat can be a challenging aspect of production. Total N application normally ranges from 90 to 120 pounds per acre, but this will vary depending on the previous crop, soil type and rainfall after application(s). Timing N application depends on several factors. The wheat crop needs adequate N in the fall and early winter to establish ground cover and properly tiller; however, excessive levels of fall N can result in rank growth which increases lodging potential and the risk of spring freeze damage due to early jointing or heading. If the wheat crop is following soybeans, soil residual or mineralizable N should be adequate for fall growth, and no pre-plant N is needed. However, if the wheat crop follows corn, sorghum, rice or cotton, the application of 15 to 30 pounds of N per acre would typically be beneficial. Where the wheat crop is planted later than the optimum date, additional N may be necessary to ensure adequate fall growth prior to winter conditions. If the wheat crop did not receive a fall application and appears to be suffering from N deficiency in January, the initial topdress N application can be made early to promote additional tillering. The majority of N for the wheat crop should be applied in early spring. There is no universal rule on how early spring N should be applied. Each field should be evaluated based on tillering, stage of development, environmental conditions, and crop color. A crop that has good growth and dark green color should not need N fertilization prior to erect leaf sheath (Feekes 5), usually sometime in early to mid-February. However, first spring fertilizer application should be applied prior to first node (Feekes 6) to ensure optimum head development, tiller retention and head size. If the plants are light green (chlorotic) in January it may be necessary to apply the first N in mid-January. If sulfur was not applied in the fall it may be necessary to include S with the first N application. Crop N stress around jointing (Feekes 6) will result in yield loss. Any additional N applied following flag leaf typically contributes very little to crop yield. Splitting topdress N into two or three applications is common in Louisiana production systems due to the increased risk of N losses often associated with heavy rainfall and our long growing season. Splitting N typically occurs by applying fertilizer N at or just prior to jointing with a second application occurring 14 to 28 days later when the first application has visibly greened up the crop. About 50 percent of the topdress N is normally applied with the first split, but this may be decreased if the first split is put out early and plants are not well enough developed to take up that much N.

Phosphorus, K, and micronutrients should be applied in the fall based on soil test reports. All fertilizers applied as well as lime should be incorporated into the soil prior to planting. Required lime should be applied pre-plant because it takes time for the lime to begin to neutralize the acidity of most soils. The application of sulfur is a growing concern in Louisiana production systems, with increasing deficiencies appearing every year. Early spring sulfur (S) deficiency is sometimes mistaken for N deficiency and additional S is not applied. Because sulfur is mobile, similar to N, the application solely in the fall will not be adequate. Supplemental applications of S with the first spring N applications are often warranted.

Wheat vernalization and freeze damage: Vernalization is the process whereby winter wheat develops the capacity to become a reproductive plant triggered by satisfying its requirement for a certain number of hours of cold accumulation. Vernalization occurs between 32 F and 45 F with maximum accumulation around 40 F. Most varieties require 3 to 6 weeks (504-1008 chill hours) to vernalize, but the requirement can be significantly more or fewer hours. Producers should be aware of the vernalization requirements for varieties they select. Vernalization requirement is part of the rationale in splitting the statewide wheat variety trial into north and south Louisiana regions. Some varieties suited to north Louisiana do not reliably vernalize in south Louisiana and should not be planted there.

Heading date can be an indicator of vernalization requirement but heading date is also influenced by photoperiod and some later-heading varieties have a low vernalization requirement. Heading date for each variety is published in the ‘Small Grains Performance Trials’ https://www.lsuagcenter.com/topics/crops/wheatoats/variety_trials_recommendations. In general, later-heading varieties can be planted a little on the early side of the recommend window and early-heading varieties should be planted on the late side. This information will aid producers when selecting adapted varieties. Wheat breeders in the region are actively developing varieties that have a lower vernalization requirement and rely more upon photoperiod to control heading date. This is because our weather patterns have become very unpredictable in recent years and photoperiod is constant across years.

A Fresh Look at Soil Testing: LSU AgCenter’s New Report Format

Leandro O. Vieira, LSU AgCenter Soil Fertility Specialist

The LSU Ag Center Soil Testing and Plant Analysis Laboratory has released an updated format for its soil test report (Figure 1). This effort was led by Dr. Ted Gauthier, Interim Soil Lab Director and Head of the Agricultural Chemistry Department. To accomplish this, a company was contracted to design a new system for the lab and a new template for the soil test report. I also serve as a Technical Advisor to the Soil Testing Lab and had the opportunity to contribute to this initiative.

Figure 1. The old (left) vs. the new (right) soil test report template from the LSU AgCenter Soil Testing and Plant Analysis Laboratory.

To improve visualization of soil nutrient levels, the new report features colored bars representing each level: red for very low, orange for low, light green for medium, dark green for optimum, and blue for above optimum. A change was also made to the nomenclature of the nutrient levels, in which high was replaced with optimum and very high with above optimum (Figure 2). This adjustment reflects current understanding: there is not enough data to confirm that nutrient levels in the high and very high range can cause environmental or plant health issues. In practice, the high level indicate sufficient nutrient levels for plant growth, and very high means the nutrient level is above plant needs but likely not causing yield reduction.

Figure 2. New nutrient level nomenclature: “High” was replaced with “Optimum”, and “Very High” was replaced with “Above Optimum”.

At no additional cost, the Soil Testing Lab now includes three additional micronutrients in the routine soil test report: boron (B), iron (Fe) and manganese (Mn). Soil pH and concentrations of phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), zinc (Zn) and copper (Cu) continue to be provided, as in the previous report. Sodium (Na) concentration is also in the new report. While sodium is not a nutrient for most cultivated plants, when in high concentrations, it can limit plant growth and reduce yields. Another addition to the results table is buffer pH, which will be used for future liming recommendations. Efforts are currently underway to calibrate this methodology to Louisiana soil conditions.

In response to customer requests, several new features have been added to the updated report: calculated cation exchange capacity (CEC), percentage saturation of potassium, calcium, magnesium, hydrogen and sodium in the calculated CEC, as well as potassium/magnesium and calcium/magnesium ratios. Although these features are not typically used to generate fertilizer recommendations, they can explain certain crop responses to fertilizer applications.

The LSU AgCenter Soil Testing Lab, located at 125 M.B. Sturgis Hall on the Baton Rouge campus, offers soil analysis and interpretation services for a small fee. Take advantage of soil testing to ensure your crops receive the nutrients they need to thrive: https://www.lsuagcenter.com/portals/our_offices/departments/spess/servicelabs/soil_testing_lab. If you have questions about soil sampling or interpreting soil test reports, please contact your local extension agent.

2025 Cotton Harvest Update

Shelly Kerns, LSU AgCenter Corn, Cotton and Grain Sorghum Specialist

Cotton harvest has been well underway in Louisiana for a few weeks now. Most of our state’s cotton is expected to be harvested by the end of October, with the exception of a some later planted acres. So far growers have reported picking around 1,200-1,600 lbs., with some reports nearing 2,000 lbs of raw cotton per acre. Most growers have not received reports from their gins yet, so we will have a better estimate on a state lint yield average once turnout numbers start rolling in. Regardless, we are looking well on track to smash the state yield average from the last few years.

Although we are at an all-time low for cotton acreage in Louisiana (just under 100,000 acres), our quality looks better than last year so far. The quality of the crop has many cotton growers in good spirits and looking forward to growing cotton again next year. With an overabundance of corn grown in Louisiana this year, and with increasing fertilizer and input costs, it will be interesting to see how crop trends flux again next growing season. With new incentives recently passed in the one big, beautiful bill act (OBBBA), growing cotton is becoming more favorable as the risks are being better managed through new federal programs and crop insurance options (see summary here: https://www.farmprogress.com/farm-policy/ncc-holds-meetings-to-help-farmers-understand-new-reconciliation-bill). In conjunction with these new incentives, if the markets shine in our favor as we move into next growing season, I hope to see an increase in cotton acreage next year.

Fall and Spring Options for Controlling Ragweed Parthenium

Stephen Ippolito, LSU AgCenter Weed Scientist

Most fall and spring burndown programs are centered around either 2,4-D or paraquat based applications for their broad-spectrum postemergent weed control. 2,4-D can provide control of small ragweed parthenium; however, once the plant has bolted it can be more difficult to control. Paraquat does not provide sufficient control of ragweed parthenium alone. Saflufenacil (Sharpen) at 1-2 fluid oz/a plus 1% v/v methylated seed oil can provide excellent control of ragweed parthenium; thus, is an option for fall and spring burndown.

Research conducted in 2025 found that tiafenacil (Reviton), a new PPO inhibitor, also has activity on ragweed parthenium when applied with 1% v/v methylated seed oil. Preliminary data indicates that fall applied postemergent burndown applications of tiafenacil provide excellent control of 6 inch tall ragweed parthenium, 1 week after treatment. In addition, preliminary data indicates 2 fluid oz/a of tiafenacil provides good control of 10 to 12 inch tall volunteer corn, 1 week after treatment.

Tiafenacil may be a good addition to fall or spring burndown programs for ragweed parthenium control, however, there is some potential for it to regrow. Research is ongoing to evaluate the use of residual herbicides in addition to tiafenacil for ragweed parthenium control. The maximum rotation crop interval for field corn, soybean, and cotton is 0, 7, and 14 days, respectively. Therefore, it may be especially useful for controlling ragweed parthenium before planting in the spring. For more information about products and product specific use sites please refer to the product label as well as the Louisiana Suggested Chemical Weed Control Guide for Agronomic Crops. It is the responsibility of the applicator to read in entirety and follow the label’s instructions.

Figure 1. Control 1 week after treatment, from saflufenacil at 1 fluid oz/a (A) and tiafenacil applied at 1-3 fluid oz/a (B-D) to 6 inch tall ragweed parthenium, compared to a nontreated check (E). 1% v/v methylated seed oil was included for all herbicide treatments. Photo by Stephen Ippolito

LSU AgCenter Conducts Soybean Variety Trials at Research Stations and Farms

David Moseley and Tristan Watson, LSU AgCenter Scientists

Article Highlights:

• The LSU AgCenter evaluates soybean varieties through both replicated research station trials and on-farm demonstrations to provide regionally relevant performance data.
• Farmers are encouraged to select varieties that perform consistently across multiple environments and years to improve yield stability.
• In 2025, variety testing included evaluations for yield and abiotic/biotic stress resistance across diverse Louisiana environments and soil types.

Selecting the most well-adapted and high-yielding soybean varieties is one of the most critical decisions a farmer makes each year. To support this decision, the LSU AgCenter conducts Official Variety Trials (OVT) and on-farm Core-block demonstration plots, providing unbiased performance data to aid in variety selection. These trials are planted across multiple research stations and producer farms throughout the state, allowing data collection in diverse environmental conditions.

When choosing a variety, it is important for farmers to consider how it performs in environments similar to their own, as well as across a range of conditions. Varieties that consistently perform well across multiple locations and years are generally considered to have greater performance stability.

Official Variety Trial

The 2025 OVT included varieties with maturity groups ranging from 4.0 – 5.7. The maturity groups are divided into sections including 4.0 – 4.4; 4.5 – 4.7; 4.8 – 4.9; 5.0 – 5.3; and 5.4 – 5.7, and there were 10, 19, 28, 4, and 7 varieties submitted to the maturity group sections, respectively. Ten seed companies and one soybean breeding program participated in the 2025 OVT. The varieties consisted of several different herbicide technologies. The trial was replicated at seven research stations across the state in different soil types including fine sandy loam, silt loam, and silty clay. At each location, the varieties were replicated four times.

On-farm Core-block Demonstration Plots

In addition to the OVT, the LSU AgCenter collaborates with soybean farmers to evaluate soybean varieties directly on farms. For the Core-block demonstration program, the LSU AgCenter parish agents cooperate with farmers to plant, maintain, and harvest strip trials submitted by seed companies and university soybean breeding programs. These demonstrations provide valuable data from across the state and in local growing conditions and agronomic practices.

In 2025, six seed companies submitted varieties to be evaluated in the Core-block demonstrations. Twenty-five demonstrations were planted across 11 parishes. The number of demonstrations for each MG section were 5, 12, and 8 for the MG sections of 4.1 to 4.4; 4.5 to 4.9, and 5.0 to 5.5, respectively. The number of varieties submitted for each MG were five (MG 4.1 to 4.4), eleven (MG 4.5 to 4.9) and five (MG 5.0 to 5.5).

In addition to on-farm variety trials that focus on yield, a total of eight varieties (seven entered as resistant and one susceptible) from three companies were entered into the nematode resistance screening trial. The varieties were planted in three parishes (Franklin, Tensas, and Bossier) in fields known to have nematode pressure. Data included nematode assays and yield. To complement this trial, a replicated small-plot trial was also planted. Several soil and plant samples as well as greenhouse trials were conducted to determine the level of resistance for each variety.

Figure 1: A soybean variety showing early senescence due to root-knot nematode feeding in a field near Bossier City, LA during the 2025 growing season. Photo credit: Tristan Watson.

Figure 2: A soybean variety showing a patchy stand, stunting of growth, and early chlorosis at a root-knot nematode infested field near Bossier City, LA during the 2025 growing season. Photo credit: Tristan Watson.

Figure 3: A mature root-knot nematode female excised from within soybean roots showing galling symptoms at a root-knot nematode infested field near Bossier City, LA during the 2025 growing season. Photo credit: Tristan Watson.

Variety Testing and On-farm Demonstration Results

The performance data from the soybean OVT and on-farm demonstrations will be published by the LSU AgCenter in the annual soybean variety testing summary. Maturity date, height, lodging, and disease reaction information from the OVT will also be included. The 2025 OVT results will be published following harvest to assist with 2026 variety selections and planting decisions.

The variety publication for previous growing seasons (and the 2025 growing season when available) can be found at LSU AgCenter Soybean Variety Data.

For more information on soybean variety testing and selection, please read the article Using Variety Testing Data to Select Soybean Varieties: Guidelines for Practitioners, published in Crop, Forage & Turfgrass Management. This article presents practical methods for evaluating soybean varieties through both replicated small-plot trials and unreplicated on-farm demonstrations. It highlights the value of assessing variety performance across a range of environmental conditions and features examples from Louisiana-based trials. Additionally, it discusses key stress tolerance traits, including chloride toxicity and resistance to nematodes.

Cotton Jassid Update – October 2025

James Villegas and Dawson Kerns, LSU AgCenter Field Crop Entomologists

Cotton jassids have now been confirmed in multiple locations across Louisiana, expanding beyond the initial detections in Tensas Parish. In addition to the two cotton fields in Tensas, cotton jassids have also been found in cotton regrowths in Franklin, West Carroll, Rapides, and Pointe Coupee Parishes, as well as in okra plants in Tangipahoa Parish. These findings suggest a broader distribution of the pest across the state.

These small (2 mm), pale green insects with translucent wings and distinct black spots on each wing tip feed on the undersides of leaves. Their piercing-sucking mouthparts inject toxins that cause “hopperburn” in cotton, a condition marked by yellowing, curling, and browning of leaves. Symptoms often appear first on field edges and may be mistaken for potassium deficiency. Severe infestations can result in leaf drop, stunted growth, and reduced yields.

Cotton jassids are native to the Indian subcontinent and were first detected on the U.S. mainland in Florida in 2024. They feed on a wide range of host plants including cotton, okra, eggplant, hibiscus, and other solanaceous and ornamental species. In endemic regions, uncontrolled infestations have led to yield losses of up to 50% in cotton.

In response to these detections, monitoring efforts were initiated to track the spread across the state. We will know more about success of cotton jassid overwintering in the spring. Early detection and coordinated response will be key to control this pest.

Anyone who suspects the presence of cotton jassids in their crops or garden plants should contact their local extension agent or reach out directly to LSU AgCenter Field Crop Entomologists James Villegas (jvillegas@agcenter.lsu.edu, 225-266-3805) or Dawson Kerns (ddkerns@agcenter.lsu.edu, 806-474-7220).

Close up photo of cotton jassid adult (left) and nymph (right). Photos by J. Villegas.

What is Plant-Growth Promoting Bacteria and why should its addition be investigated?

Saulo Augusto Quassi de Castro, LSU AgCenter, Sugarcane & Soybean Agronomist and David Moseley - LSU AgCenter, Soybean Specialist

Biotic (e.g., diseases, pests, and weeds) and abiotic stress (e.g., drought, and heating) are commonly faced by crops in Louisiana. While some of them can be attenuated by using agrochemicals, such as fungicides, insecticides, and herbicides, abiotic stresses are harder to bypass and have no products that can mitigate the damage promoted in the plant. To improve plant resilience and help plants recover from abiotic and biotic stress, respectively, biostimulant have been used by farmers and successful cases have been reported worldwide.

Biostimulant is, as it is in the name, any product (chemical or biological) that stimulates plant growth. The mechanisms of action are not well described, triggering science. However, benefits have been reported in crop yield and quality, nutrient use efficiency, and plant tolerance to abiotic and biotic stress among others (Carillo et al., 2025; Khoso et al., 2024). Due to this broad spectrum, farmers are adopting this technology and the biostimulant market has become a huge industry in the last few years. Among several types of biostimulant, Plant-Growth Promoting Bacteria (PGPB) has an important position.

Plant-Growth Promoting Bacteria colonizes the rhizosphere, that is, the soil which surrounds the roots of the plants stimulating plant and, mainly, root growth. Their benefits also include phytohormone production, plant pathogen control, abiotic stress tolerance, and increased nutrient availability, including biological nitrogen fixation (BNF) and phosphate solubilization (Figure 1). PGPB also acts in the mineralization of organic matter, transforming nutrients present in organic sources into inorganic forms that are absorbable by plants.

Figure 1. Plant-Growth Promoting Bacteria functions in enhancing plant growth and stress resistance. Source: Etesami et al. (2025).

Among several PGPB genera, Azospirillum spp and Bacillus spp are widely studied aiming to improve root growth (Figure 2). A vigorous and high-yielding crop relies on the health, size, and activity of the plant root. With a robust root system, plants can grow and develop well because roots will explore the soil profile more, increasing the water and ions available to the plant and resulting in great potential yield and quality.

Figure 2. Root biomass of grass Marandu palisade inoculated with Azospirillum brasilense (AB), Bacillus sp. (EB) or with both microorganisms (MIX) compared to non-inoculated plants (C). Source: Terra et al. (2024).

Aiming to get the previously mentioned benefits and bypass adverse climate features, root growth must be improved which can be promoted by PGPB. To investigate these effects in soybean cultivated in Louisiana, field trials were carried out at Dean Lee Research and Extension Center with different soybean maturity groups and in clay and silty loam soil. Trials were also carried out at Iberia Research Station with one soybean maturity group. The trials were harvested in October, and data will be presented in the next Louisiana Crops Newsletter.

References

Carillo, P., Avice, J.-C., Vasconcelos, M.W., du Jardin, P. and Brown, P.H. (2025) Biostimulants in Agriculture: Editorial. Physiologia Plantarum, 177: e70046. https://doi.org/10.1111/ppl.70046

Etesami, H. (2025) The dual nature of plant growth-promoting bacteria: Benefits, risks, and pathways to sustainable deployment. Current Research in Microbial Sciences, 9, 200421. https://doi.org/10.1016/j.crmicr.2025.100421

Khoso, M.A., Wagan, S., Alam, I., Hussain, A., Ali, Q., Saha, S., Poudel, T.R., Manghwar, H., Liu, F. Impact of plant growth-promoting rhizobacteria (PGPR) on plant nutrition and root characteristics: Current perspective. Plant Stress, 11, 100341. https://doi.org/10.1016/j.stress.2023.100341

Terra, L.E.d.M., Santos, M.M.d., Lopes, M.C.S., Pinheiro, D.A., Lopes, É.M.G., Soares, A.S., Braz, T.G.d.S., Nietsche, S., Cota, J. (2024) Co-Inoculation of Azospirillum brasilense and Bacillus sp. Enhances Biomass and Photosynthetic Efficiency in Urochloa brizantha. Agriculture, 14, 2349. https://doi.org/10.3390/agriculture14122349

LSU AgCenter Specialists