Wheat Variety Performance and Production Practices in Louisiana

Boyd Padgett, Stephen Harrison, Noah DeWitt, and Trey Price, LSU AgCenter Scientists

Article Highlights:

• Variety selection considerations (vernalization/heading date, disease resistance, yield, test weight)
• Crop management (planting date, seeding rates, fertilization strategies)

To access the Variety Performance Trial publications, go to the following website:

Varieties

Variety selection:

Choice of varieties for planting is a crucial management decision that sets the stage for yield potential and input costs. While grain yield is the most important factor, test weight, disease resistance, and heading date are important considerations as they also impact economic return.

Test weight is important because low test weight results in dockage at the elevator. Heading day is a function of cold requirement (vernalization) and day length (photoperiod) response that determines when a variety heads out. Some varieties head very late or not at all in south Louisiana due to a long vernalization requirement or photoperiod response, while those same varieties may perform better in north Louisiana or Arkansas. Varieties that fully vernalize but head out late due to long photoperiod requirement perform poorly in south Louisiana due to grain fill during hot weather. By contrast, early heading varieties may yield poorly in north Louisiana due to late spring freeze damage. Vernalization and photoperiod response are the primary reasons for dividing Louisiana into North and South regions.

Early-heading and maturing varieties permit earlier harvest and more timely planting in a double-crop system, while later-heading varieties guard against damage from a late spring freeze and can be planted earlier in north Louisiana. Early-heading varieties should be planted in the second half of the recommended planting window to reduce the likelihood of spring freeze damage. Lodging resistance helps guard against reduction in test weight and yield loss that results when near-mature heads come in contact with the ground.

Disease resistance protects yield and reduces input costs. Disease susceptibility is very important in terms of yield and profitability. Reactions for naturally-occurring diseases are also listed for each variety in Variety Performance Trial publications. There are no varieties fully resistant to FHB, but some have high to moderately high to moderate levels of resistance. It should be noted that varieties less susceptible to disease may not always be the highest yielding, especially if disease pressure is not present. However, in high disease pressure situations, these varieties produce higher yields than susceptible varieties and enhance profitability by saving the costs of fungicide applications.

Crop management:

Planting dates for Louisiana wheat depend on location and variety. For southern and central Louisiana, optimum planting dates range from November 1 through November 30. The optimum planting for northern Louisiana is slightly earlier, ranging from October 15 through November 15. Early-heading varieties should generally be planted after the mid-date, while late-heading varieties can be pushed a little on the early side of the planting window. The weather in north Louisiana is cooler in the fall and early winter, which slows growth and prevents excess winter growth. It is important that the wheat crop be well-established and fully tillered before the coldest part of the winter. Additionally, because of the cooler conditions, the threat from fall pests (Hessian fly, army worms and rust) is decreased earlier in the fall compared to south and central Louisiana. While these dates are the optimum planting window averaged over years, the timing will vary in some years depending on weather patterns. Additionally, if wheat cannot be planted within these optimum windows, planting later than the optimum window is usually better than planting too early. Early planting can result in greater insect and fall rust establishment and also makes plants more prone to spring freeze injury due to excessive fall growth and development. Planting too late (more than 14 days after the optimum window) can result in significant yield loss due to slow emergence, poor stands from seed rotting and a decreased tillering period, which results in fewer and smaller heads.

Wheat can be planted by broadcasting seed and incorporation into the soil; however, it is preferred that the seed be drilled. Drilling the seed increases the uniformity of depth and uniform emergence. Use recommended planting rates for drilled wheat (60 to 90 lb/A) or broadcast wheat (90-120 lb/A) of quality seed into a good seedbed with adequate moisture. This higher seeding rate should be used under conditions in which good germination or emergence is not expected, as occurs with late-planted wheat or heavy, wet soils. Late-planted seed should be planted at a higher seeding rate using a drill to ensure rapid, adequate and uniform emergence.

Good surface drainage is critical to successful wheat production. Saturated fields lead to diseases such as root rots and downy mildew, reduced tillering and vegetative growth, and decreased root development and nutrient utilization. Yields in wheat fields suffering from waterlogging stress are greatly reduced. Fields with marginal drainage should be ditched to ensure that water stands for a minimum time after heavy rainfall.

Nitrogen (N) fertilization of wheat can be a challenging aspect of production. Total N application should normally range from 90 to 120 pounds per acre, but this will vary depending on soil type and rainfall after applications. Timing of 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 and increased lodging potential, as well as a higher probability of spring freeze damage from early heading. If the wheat crop is following soybeans, soil residual or mineralized 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 20 pounds of N per acre would typically be beneficial. Where the wheat crop is planted later than optimum, 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 top dress N application can be made early to promote additional tillering. Early spring is when the majority of N for the wheat crop should be applied. 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 good color should not need N fertilization prior to erect leaf sheath (Feekes 5), usually sometime in 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. Crop N stress around jointing (Feekes 6) will result in yield losses. 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. 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 as soon as possible 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. Oftentimes, early spring sulfur (S) deficiencies are mistaken for N deficiencies and additional S is not applied. Because sulfur is mobile, similar to N, the application solely in the fall may not be adequate. Supplemental applications of S with spring N applications are often warranted.

For further questions or comments contact:

Steve Harrison, Small Grain Breeder, sharrison@agcenter.lsu.edu

Noah DeWitt, Small Grain Breeder, ndewitt@agcenter.lsu.edu

Boyd Padgett, Wheat Extension Specialist/Plant Pathologist, bpadgett@agcenter.lsu.edu

Trey Price, Extension Research Plant Pathologist, pprice@agcenter.lsu.edu

 

Optimizing Italian ryegrass control with fall applied residual herbicide and cover crop

Donnie Miller and Stephen Ippolito, LSU AgCenter Weed Scientists

Italian ryegrass has become a serious problem for Louisiana producers and if left uncontrolled can reduce crop yield. Ryegrass is currently the most troublesome winter species in corn, cotton, and soybean. If growers can’t control the grass, it becomes a tremendous competitor with crops, especially those planted early, such as corn, which reduces yield for producers. The weed may also host insect populations, which is doubly problematic. Often, attention is not focused on later-emerging spring populations or earlier misses in control until it’s too late. The size of later-emerging spring populations or earlier missed ryegrass, along with resistance development to once effective postemergence herbicide options, limits effective control at that time.

Research initiated in fall of 2022 and expanded in fall of 2023 and 2024 has shown that the use of cover crops and/or soil residual herbicides applied in the fall after harvest can be effective tools in combatting spread. Cereal rye at a seeding rate of 80 pounds per acre can effectively compete with emerging ryegrass and limit tiller and seedhead production. Ryegrass tiller number reduction in both years was good to moderate (43 and 81%) in spring with only cereal rye planted in fall and reduced 50 and 45% with only S-metolachlor applied in the fall at 1.33 pints. The combination of the two, however, resulted in a 95 and 97% reduction by spring. Seedhead production was only significantly reduced by the combination (93%) in spring of 2024 but was reduced by the cereal rye (81%) and S-metolachlor (41%) in 2025 in addition to the combination treatment (97%).

A second part of this approach is identifying optimum timing for herbicide application in relation to cover crop and ryegrass emergence. Unfortunately, these species often emerge simultaneously, so having the herbicide out as early as possible is most beneficial. Research initiated in the fall of 2023 and repeated in 2024 has shown that some residual herbicides, such as S-metolachlor or pyroxasulfone, can be applied at the spiking stage (80% or greater cereal rye or black oat plants emerged through soil), while others such as metribuzin and clomazone are much better tolerated when applied two weeks after emergence to one- to two-leaf plants. Plant injury with these two herbicides, however, is greater than with S-metolachor and pyroxasulfone at this timing as well.

A non-injureous soil residual herbicide applied soon after cover crop emergence in fall offers producers an effective program for managing ryegrass during winter and spring months ahead of planting. In addition to weed management, agronomic and soil benefits associated with cover crops are realized. This combination offers a one-two punch approach to ryegrass management, allowing the soil herbicide to eliminate or limit emergence of ryegrass during late fall and early winter months while the cover crops limit spring emergence and competition from plants not controlled in fall due to prolific biomass production in spring.

Ryegrass control four weeks prior to soybean planting in spring with a cereal rye cover crop treated over-the-top with Dual Magnum (S-metolachlor) two weeks after emergence in the fall. Photo by Donnie Miller

Ryegrass population four weeks before soybean planting with no treatment or cover crop used in the fall. Photo by Donnie Miller

 

Cleaning Equipment to Prevent the Spread of Weed Seed

Stephen Ippolito and Donnie Miller, LSU AgCenter Weed Scientists

Following mowing, disking, spraying, and harvest operations, weed seed can “hitch a ride” on farm equipment, allowing populations to infest new locations (Image 1). Routine cleaning of farm implements prior to relocation is especially important for preventing the spread of troublesome and herbicide-resistant weeds in Louisiana including prickly sida (teaweed), johnsongrass and Palmer amaranth. This practice should include all equipment that enters the field, even smaller equipment such as pickup trucks and ATV’s (Image 2). With harvest underway here are some mitigation practices which can help to prevent the spread of weed seed.

Mitigation practices:

• Harvest order: If possible, consider harvesting fields in order from lower to higher weed densities. It is important to harvest fields which are suspected to have herbicide resistant populations last.
• Sanitation: Whether planting, spraying, harvesting or performing any other activity in the field; before moving to a new field, clean all equipment that entered the field.

Figure 1. Palmer amaranth and yellow foxtail growing from mulch on the back of a rotary cutter. Photo by Stephen Ippolito

Figure 2. Weed seeds on the bumper of a pickup truck. Photo by Stephen Ippolito

Image 3. (A-G) Below shows examples of cleaning equipment and where machinery should be cleaned. Photos by Stephen Ippolito

(A) Equipment should be cleaned in the field it was used in. A leaf blower or compressed air can be used to clean equipment. With the amount of dust and debris, wearing a dust mask and eye protection is recommended. Before cleaning, allow the combine to run for a few minutes to clear as much debris as possible. To prevent the seed from naturally dispersing through wind or water, residue should be contained as best as possible and destroyed.

(B) Clean top to bottom, starting with the hopper and then working down.

(C) Open all side panels to blow off the exterior of the combine.

(D) Clean the combines’ header of all debris. When time allows, it may be a good idea to remove the header for a more thorough cleaning.

(E) Open the side panels on both sides to blow out both the rotor and below it.

(F) Open both elevators and blow out any debris.

(G) Make sure to check the entirety of the combines exterior.

 

Green Stem in Soybean

David Moseley and Stephen Ippolito, LSU AgCenter Scientists

There have been several cases of green stem reported in mature (R8) soybean fields. A Science for Success factsheet (Understanding Green Stem in Soybeans) explains that green stem is a disorder where the stems of a soybean plant stay green after the pods have fully matured. The exact cause of green stem is unknown. However, it is generally associated with any factor that reduces pod and seed development. This is because the developing seeds are the "sinks" that draw nutrients from the plant's "sources" like the leaves and stems. When the seed production is reduced, nutrients can be retained in the stems and the stems can remain green. One of the commonly associated factors is environmental stress, which can lead to premature loss of pods and seeds. Generally, green stem does not appear to limit yield however it can severely reduce harvest efficiency. The green stems can clog or choke harvesting equipment. Operators may need to decrease combine speed if there are too many green stems. However, in some cases it has been observed where environmental stresses have seemed to cause green stem and a severe loss of yield.

Additional information can be found in this Crop, Forage, & Turfgrass Management article. A self-study CEU is available from Crops & Soils magazine where CCAs can earn credit on green stem if they read the Crop, Forage, & Turfgrass Management diagnostic guide and answer the quiz questions found at this Crops & Soils magazine link.

Figure 1. Leaves remaining on mature soybean plants after applying a harvest aid.

Figure 2. Soybean stems remain green after the pods have matured.

Figure 3. Green pods and stems can cause issues in harvesting.

Figure 4. Variety differences in green stem were observed on a farm.

Figure 5. Soybean plants that have been at the R8 growth stage for several weeks, but their stems and branches have remained green. In addition, although there are several pods per plant, the seed count per pod is very low.

 

LSU AgCenter Specialists

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	Daniel Stephenson	318-308-7225
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