Progress report for LNC21-451
Wheat is a preferred crop in water limited environments due to its water use efficiency, beneficial residue produced, and ability to produce good yields under a wide range of environmental conditions. Wheat residue can suppress weeds, reduce erosion, increase soil health, capture snow, and enhance precipitation storage efficiency. Production of wheat is being threatened by wheat stem sawfly which cuts the stem near the base and lodges the tiller holding the grain head before harvest. This reduces wheat yield, slows harvest, and greatly diminishes the benefit of the residue. Previous research has found that attributes of the wheat stem wall (thickness) mitigate the impact of the wheat stem sawfly. Even when sawfly pressure is low, increased stem wall thickness and composition increase standability of the wheat before and after harvest, and this could lead to longer-lasting residue and increased subsequent soil water storage and crop yields. This project will evaluate the stem thickness of wheat varieties and how that may reduce sawfly survival and lodging. Furthermore, the project will aim to understand how sawfly infestation may reduce wheat grain yield and quality, residue persistence/degradation, and soil water content and health. More broadly, the implications from understanding stem thickness and its potential impact on soil water can guide breeding and variety selections to impact cropping systems favorably through benefits of strong and persistence of wheat residue. It is anticipated that crop yields of the following crop can be increased when seeded behind a wheat that enhances soil water content. Lastly, the project will evaluate wheat residue characteristics through growing phases until harvest to see if any potential forage benefits exist. These results will be shared widely with wheat producers, wheat breeders, and industry personnel through Extension and outreach efforts.
Wheat producers, agronomists, and wheat breeders will gain insight and quantitative metrics into the value of selecting and using wheat varieties with beneficial stem characteristics that reduce susceptibility to wheat stem sawfly and enhance precipitation storage efficacy. Wheat producers who face yield losses from wheat stem sawfly will gain a greater understanding of the impact of the pest on grain yield, harvestability, and wheat residue degradation. Results will be shared through field days, conference presentations, Extension outlets, and peer-reviewed publications. Field days hosted at the on-farm locations will be especially impactful because we plan to include large plot demonstrations.
In many areas of the Northern Great Plains, wheat stem sawfly (WSS), Cephus cinctus, is threatening wheat production and lodging wheat. The impact this has on residue degradation and the subsequent crop is unknown. Wheat stem sawfly is an important pest of wheat throughout the Northern Great Plains. Wheat stem sawflies feed on hollow-stemmed grasses, such as most of our high-yielding wheat varieties. The wheat stem sawfly reduces grain yield while feeding inside the stem (Holmes 1977). Most notably, this insect also causes lodged wheat as it girdles the stem to form overwintering pupation chambers within the base of the stem. Harvesting these lodged wheat plants is very difficult or impossible, resulting in further yield loss. Wheat production practices that are beneficial to soil and moisture conservation (e.g., summer fallow, reduced or no-till) are also thought to encourage wheat stem sawfly survival. Over the past two decades, reduced tillage and no-till wheat has been widely adopted in wheat growing regions. The benefits of these tillage practices are clear; however, evidence from our western growing areas indicates that this environment is also favorable to this pest insect (Criddle 1922, Weiss and Morrill 1992). In severe years of sawfly lodging, crop losses from this insect in the Northern Plains have exceeded $25-$80 million dollars (Kappel et al. 1996). Recent efforts in Nebraska and other states have focused on breeding solid-stem traits into local wheat varieties.
When wheat stems are weakened or lodge prematurely, we hypothesize they will degrade more rapidly and provide fewer ecosystem services. The tradeoff with wheat varieties that have solid stems or more dense stems is that there is a secondary sink to photosynthate that is generally diverted from grain, thus reducing yield potential by up to 30% (Creech, personal observation). Using a whole rotation and systems approach, the losses to grain yield in the wheat crop may be made up for in other ways. Benefits from increased stem wall thickness and structure include reduced grain loss due to lodging from wheat stem sawfly pressure, significant weather events, or poor stand. After harvest, standing wheat residue typically helps capture snow and hold moisture at the surface and soil water content in the next year is subsequently increased. Wheat residue also plays a role in natural weed suppression, thus decreasing reliance on chemical weed control. Together, these advantages can provide benefits to system productivity, resilience, and long-term viability for producers in wheat producing areas.
The use of sawfly tolerant wheat will not only improve wheat yields but will enhance subsequent crop yields due to decreased rate of residue degradation.
Objective 1 - Wheat Residue Characteristics and Forage Quality
Research will be conducted at University and farmer cooperator locations near Hemingford, Sidney, and Grant, NE. In the early part of September 2021 and 2022, 12 hard red winter wheat varieties will be seeded using a no-till drill in 5ft by 30 ft plots. These plots will be arranged in a randomized complete block design with four replications. Seeding rate will be 800,000 PLS per acre based on optimal seeding recommendations for the region. Fertility will follow university recommendations and pest/diseases will be managed to limit impact on yield. The 12 varieties selected will represent different stem characteristics. These will include solid-, semi-, and hollow-stemmed varieties. Other characteristics that will be included are varieties classified as weak stemmed, strong stemmed, short, tall, and those with high grain yield and/or forage potential.
Each location will be monitored for the presence of wheat stem sawfly throughout the growing season. When the first sawflies are observed, sweep sampling will commence with sampling twice weekly throughout the flight period, which generally lasts 2-3 weeks At the onset, peak, end of the sawfly flight, and just prior to wheat harvest, wheat biomass samples will be collected from each plot by cutting half a meter of an inner row of wheat near the soil. At this point, the wheat stem sawfly has not caused damage to the wheat stem. After weighing the sample, five wheat stems will be selected and cut in the middle of the lowest, middle, and highest internode of the stem. At each cut, the stem wall thickness will be measured using a caliper with a 0.01 mm resolution. Biomass samples will then be composited by variety at each location. The plant material in each of these composited samples will then be divided into two subsamples consisting of stem only and leaf tissue and weighed. Subsamples will then be oven dried to constant weight and weighed again. These subsamples (24 total/location/sampling period) will be sent to Ward Labs for forage analysis to identify the amount of lignin, nitrate, and other forage metrics.
Stem wall thickness at different sampling periods, along with the forage analysis of the stems (specifically lignin), will be evaluated for correlations to wheat stem sawfly survival (Objective 2). Forage analysis will also be used to evaluate how forage quality changes over time with different wheat stem characteristics. These data will be analyzed using a combination of split-plot-in-time and multivariate statistical analysis methods as needed.
Objective 2 - Wheat Stem Sawfly Survival and Impact on Wheat Yield
The same locations and plots utilized for objective 1 will be used for Objective 2. To sample adult sawflies, sweep net samples will be taken biweekly from each plot as also described in Objective 1. More specifically, individual samples per site will consist of 10 sweeps that will be taken while walking parallel to the direction of the row and sweeping through the upper third of the wheat canopy with a 38-cm sweep net. A 180° arc across the rows will be considered one sweep. Sampling will begin in early May and continued through June, when sawflies were no longer present. Through this same method, sawfly parasitoids (i.e., Bracon spp.) will be sampled and counted to monitor their presence as high level of sawfly parasitoids can affect sawfly larval survival. All samples will be bagged and returned to the lab for counting and sex determination for sawflies.
Within each plot, two individual wheat stem samples will be randomly selected following the adult flight period and prior to harvest. Each stem sample will consist of all the wheat stems within 1 meter of a single wheat row. All stems from these samples will be split to check for sawfly larval presence and status. Visual confirmation of a larva, a larval cadaver, pupation chamber of a Bracon sp. (sawfly parasitoid), or larval frass trail will be counted as larval presence.
At the Sidney location, we will set up sawfly exclusion cages in each plot. Prior research has indicated that there is a large enough wheat stem sawfly population at this location that un-infested wheat tillers are rare. Therefore, within each plot an ~ 1-m2 cage (Bioquip Collapsible Field Cage #1451D) will be installed. The cage frames will be covered with a sawfly-exclusion mesh before the onset of the flight period. This will ensure a sample of wheat from each plot with no or very low sawfly infestation for comparative analysis within a location, removing the confounding effects of site conditions and weather.
Grain yield will be performed at each location to assess the value of sawfly-resistant wheat using either plot or commercial combines as needed. Yield estimates will be adjusted based on final plot area and corrected to standard moisture.
At Sidney, we will assess individually the grain yield and grain count per wheat tiller between the infested and un-infested subplot area. Wheat heads from the 1-meter sawfly larval sampling above will be saved and compared to an equivalent number of wheat heads from sawfly-exclusion subplots. Comparison of grain mass and quality (as measured by grain protein and volumetric weight) between infested and un-infested tillers for resistant and susceptible varieties will inform the value of the sawfly resistant trait.
Objective 3 - Wheat Residue Degradation, Soil Water Content, and Soil Health, and Nutrient Cycling
Residue recovered from Objective 2 will be composited by variety for a residue degradation experiment. Using infested and un-infested wheat from the Sidney location, small samples of approximately 1 kg (12 varieties x infested vs un-infested = 24 treatments) will be weighed and placed evenly on a bare soil surface at Sidney. Each treatment will be replicated four times for each sampling period (24x2x4=144). These individual samples will each have an enclosure placed over the top to keep residue from blowing away. This enclosure is a 2x4 wood frame measuring approximately 30 cm by 30. The top is covered in a wire mesh to allow moisture and light in but keep the residue from escaping in order to simulate true degradation over time. Weighing and quality sampling will occur the following year when corn is normally planted (mid-May), and when corn matures (end of September). When collected, samples will be gently rinsed to remove soil, dried to constant weight, then weighed. This weight would then be compared to the beginning weight to estimate the rate of decomposition of the treatments.
The amount of standing and lodged residue will be monitored over time after wheat harvest until corn harvest the following year. Standing residue and lodged residue will be collected separately from a 1m by 1m area within each plot. Standing residue will be weighed. Lodged residue recovered from the soil surface will be lightly rinsed, dried until constant weight, then weighed. Weights will be compared to total biomass collected at harvest to determine rate of decomposition., Sampling interval will be August, October, March, May, July, September.
Soil Water Evaluation
To facilitate the impact of different residue characteristics on soil water, subsequent crop yield, soil health, and nutrient cycling, large plots are needed. To accomplish this, large 305-m2 exclusion cages will be set up over plots of solid-, semi-solid-, and hollow-stemmed wheat varieties alongside uncaged plots (6 total treatments) during the sawfly flight period. Each bulk plot (caged or uncaged) will be assessed for sawfly infestation using the above-mentioned method. Prior to harvest, wheat biomass production will be measured by cutting 3 half meter rows of wheat and weighing them. Grain will be harvested from these plots with a 32 ft stripper header to preserve a maximum amount of residue and reflect practices of progressive farmers in the region. These large plots will be established in Sidney in the fall of 2021 and 2022, monitored for sawfly in 2022 and 2023, and corn will be grown the following year after wheat harvest in 2023 and 2024 and harvested to measure yield differences.
Neutron access tubes will be placed in the center of each large wheat plot following establishment to measure soil water content over time at 15 cm intervals for up to 1.5 meter depth (total soil profile). Following corn emergence, access tubes will be placed within the corn row near the center of each plot. Soil water content would be measured at wheat planting, early spring, early May, and after wheat harvest. Following wheat harvest, measurements would occur once in October, and once in March. Once corn is planted and the tubes are re-installed, measurements would occur twice a month until the corn has reached maturity.
Soil Quality and Nutrient Cycling
Soil samples will be collected using a handheld soil probe at 0-8 in to monitor nutrient cycling and soil health over time. At each sampling interval 12 cores will be collected from each plot area and composited. The soil samples will be analyzed for bulk density, compaction, soil chemistry including carbon, particulate organic matter, NPK, pH, electrical conductivity, cation exchange capacity, and soil biological properties, including respiration and microbial biomass and enzyme activity. Sampling intervals will occur following wheat harvest, at corn planting, and at corn harvest. Depending on results, the sampling may extend into the subsequent cropping season.
Objective 4 - Grower and Consultant Engagement and Knowledge Transfer
This project will be successful because growers and consultants are engaged in the research process and can use the conclusions from Objective 1-3 to increase knowledge to improve efficiency and sustainability. Much of these efforts are outlined in the output and outreach sections of this proposal. The High Plains Ag Lab advisory board consists of area farmers and ag professionals and helps guide our research and extension efforts. This group will be leveraged throughout this project to ensure we are achieving our objectives and reaching our target audiences. While this research was precipitated to address farmer needs in the Northern Great Plains and areas affected by wheat stem sawfly, the conclusions will also be able to guide wheat producers across North America and other wheat growing regions by thoroughly appraising how residue quality impacts productivity and changes over time. This type of comprehensive examination of wheat residue does not have a strong presence in academic/research literature or in Extension publications.
2022 Research Results
Small Exclusion Cage Experiment:
Soil Type: Duroc loam and Alliance loam in Field 16 of the High Plains Ag Lab
Previous Crop: Millet fallow
Tillage Method: No-Till
Planting Date: 09/16/2021
Harvest Date: 07/13/2022
Seeding Rate: 900,000 seeds per acre
- Wheat was harvested using a Zurn 150 plot combine. Yield, test weight, and moisture was collected in the field using a Harvest Master H2 Classic Grain Gauge.
- Smaller exclusion cages were built randomly within plots to allow for non-infested biomass and seed to be collected.
- Other study locations included in Box Butte County and at the Stumpf Memorial Farm in Grant, cages not replicated at other locations.
Understanding the Results
- No conclusions are available for this study yet, but the study is being repeated in the 2022/23 field season. We are currently splitting stems and quantifying sawfly infestation levels among the different varieties compared to un-infested stems.
Large Sawfly Exclusion Experiment
Soil Type: Duroc loam and Rosebud loam in Field 22 of the High Plains Ag Lab
Previous Crop: Fallowed corn
Tillage Method: No-Till
Planting Date: 09/15/2021
Biomass collected: 07/18/2022 (first round)
Seeding Rate: 60 lbs/A
- Three wheat varieties were used, a hollow stem, semi-solid stem, and solid stem to compare stubble quality and persistence over time.
- Varieties planted in 15-foot strips; cages were built across all three varieties in randomized locations within reps.
- Cages used exclusion netting intended to prevent sawfly entry to protect wheat growing under the canopy.
- Wheat was harvested using a Shelbourne stripper header and individual plot yields were not calculated but instead for biomass in subsequent experiment.
- Soil water will be monitored over the next year.
Residue Degradation Study:
Wheat sub samples have been collected and place in boxes to measure degradation over time. This was initiated in the fall and will be measured through the 2023 year.
Samples and measurements are still taking place. We hope to be finished in April 2023 before new samples start to arrive from the current year. As such, no analysis of results have taken place.
Educational & Outreach Activities
The annual wheat field day hosted on June 21, 2022 at the High Plains Ag Lab had 130 attendees who had the opportunity to view the new research plots and discuss the approach being taken to address the issue. We shared photos and demonstrated the exclusion cages being used. Discussion was had on the sawfly experiments related to this project and the amount of interest was high. Growers are looking forward to better understanding the impacts of this pest and how it may reduce crop yields. Presenters were Amanda Easterly, Jeff Bradshaw, and Katherine Frels.
The Research on the High Plains held on February 14, 2023 was attended by 55. Jeff Bradshaw presented and discussed our efforts related to sawfly and sustainability. Since we are still processing samples, limited data was shared. Mostly was discussion on what our efforts are and what we hope our outcomes will be.