Crop residues are typically conserved in the field following harvest to improve soil health. However, such residues allow microorganisms to survive between cropping seasons and cause plant diseases. For example, on wheat, the fungus causing tan spot (Adee and Pfender 1989) has been shown to infect the crop planted after wheat if wheat residues are left in the field following harvest. Out of 16 million acres of total crops planted in North Dakota, over 7 million acres are under no-till or conservation till practices (USDA 2017). In no-till systems, post-harvest residues generally accumulate up to 10 Mg ha-1 are observed. Because of ND’s long winter conditions, decomposition of residues can be generally limited and provide conditions for microorganisms causing diseases to survive between cropping seasons. Although cultural management practices have been explored for other crops (e.g., wheat), we have limited data on the impact of such practices on the incidence of seedling pathogens, such as Fusarium, which has a broad host range. For the proposed study, we will establish trials in Carrington in the 2024 to 2026 field seasons where we have long-term studies on tillage practices and residue management. The proposed research is the first field study to evaluate the impact of tillage and residue management on seedling diseases under North Dakota soil conditions. The findings from this study will provide farmers with information on whether tillage and residue management regimes can provide an opportunity to reduce the levels of seedling pathogens such as Fusarium in the soil.

• Determine what tillage practices (no-till, reduced-till) will reduce the pathogen levels (with a focus on Fusarium).
• Determine whether management of crop residues will reduce the pathogen levels (with a focus on Fusarium)

• Information on whether crop residues left on the soil surface (e.g., corn stover) can be an inoculum source for Fusarium and compromise soybean health.
• Information on how tillage practices and residue management can reduce Fusarium levels.

Updated November 27, 2024:
Mid-year report for North Dakota Soybean Council (July 1, 2024 to November 30, 2024)

a. Research Project Title, Principal and Co-Investigators

Title: Exploring Tillage and Residue Management Options for Fusarium Disease in North Dakota.

Principal Investigator: Febina Mathew (North Dakota State University, Department of Plant Pathology

Co-Investigators: Nitha Rafi North Dakota State University, Department of Plant Pathology
and Mike Ostlie (NDSU REC, Carrington, ND)

b. Research Overview and Objectives

Crop residues are typically conserved in the field after harvest to improve soil health. However, these residues can also support the survival of microorganisms between cropping seasons, which may lead to plant diseases. In North Dakota, of the 16 million acres planted with crops, over 7 million acres are managed using no-till or conservation tillage practices (USDA 2017). Due to the state's extended winter conditions and the high carbon-to-nitrogen ratio of post-harvest crop residues, decomposition is generally limited. This creates an environment that favors the survival of disease-causing microorganisms during the off-season. Although residue management practices have been studied for various crops, such as wheat, there is insufficient data on how these practices affect the incidence of pathogens responsible for stem and root diseases in soybeans. To address this gap, we will conduct trials in Carrington during the 2024 to 2026 growing seasons, where we are already investigating tillage practices (no-till and minimum till) and residue management. This research aims to provide farmers with insights into whether tillage and residue management strategies can effectively control pathogen populations and reduce the severity of soybean diseases. The research objectives were to determine (1) evaluate the effect of tillage practices on the species diversity and abundance of Fusarium; and (2) determine the effect of crop residues (e.g., corn stover) on the species diversity and abundance of Fusarium under field conditions.

c. Completed Work: Deliverables and/or Milestones.

There were no significant differences in stand count and yield among the various tillage treatments and corn stover treatments in the respective trials.

d. Progress of Work and Results to Date

Objective 1. Evaluate the effect of tillage practices on the species diversity and abundance of Fusarium.

The field trial was conducted at the Carrington Research Extension Center in North Dakota. The trial followed a randomized complete block design with three treatments: no-till, minimum till, and conventional till. It was planted on May 20, 2024, with each treatment consisting of three 1.3-acre plots planted with a susceptible soybean variety (AG03X7) at a planting rate of 120,000 seeds per acre. Herbicides were applied on May 15, 2024 (Roundup PowerMAX-3 and Sharpen powered by Koxor), June 12, 2024 (Roundup PowerMAX-3, Select Max, and Engenia), and August 19, 2024 (Roundup PowerMAX-3). Five weeks after planting (June 20, 2024), stand count data was recorded. Additionally, soil samples were collected three times during the growing season (June 20, July 22, and August 21, 2024) from five to six spots in each plot. The collected soil samples will be used to extract DNA directly for Fusarium-specific qPCR analysis, with results to be assessed before the next planting season. The trial was harvested on October 8, 2024, and the yield and stand count data from the three tillage treatments were analyzed using ANOVA to determine if significant differences existed between the systems at a = 0.05. The results showed no significant differences in yield or stand count among the tillage treatments (Table 1 and Table 2).

Table 1: Stand Count

Df Sum Sq Mean Sq value Pr(>F)
Treatment 3 1.11E+09 552452269 1.871 0.234
Replicate 2 5.90E+08 196742261 0.666 0.603
Residue 6 1.77E+09 295225815

Table 2: Yield
Df Sum Sq Mean Sq value Pr(>F)
Treatment 3 318 159.2 2.457 0.166
Replicate 2 934 311.17 4.803 0.049*
Residue 6 389 64.79

Objective 2. Determine the effect of crop residues (e.g., corn stover) on the species diversity and abundance of Fusarium under field conditions.

The trial was established at the Carrington Research Extension Centre in North Dakota on May 29, 2024, using a randomized complete block design with three replicates per treatment (0%, 50%, and 90% of corn stover). Each plot measured approximately 25 feet long by 10 feet wide, consisting of four rows per plot at a seeding rate of 120,000 plants per acre, and was planted with a commercial soybean variety. Before spreading the corn stover on May 29, 2024, soil samples were collected to a depth of 1 meter in 10 cm increments using a hand probe (e.g., SCN soil probe) from the field trial site. During the growing season, herbicide was applied on June 25, 2024; a stand count was conducted on June 20, 2024; and additional soil samples were collected three times (June 20, July 22, and August 21, 2024) from 5 to 6 spots within each plot. These samples will be used for DNA extraction targeted at Fusarium-specific qPCR analysis before the next planting season. The trial was harvested on October 8, 2024, and yield and stand count across the three stover treatments were analyzed using ANOVA to evaluate whether the rates of stover harvest (0%, 50%, and 90%) led to significant differences. The results (Tables 3 and 4) indicated no significant differences in yield among treatments at a = 0.05, suggesting that the stover rates did not influence the cropping system's performance under the experimental conditions.

Table 3: Stand Count
Df Sum Sq Mean Sq value Pr(>F)
Treatment 3 2602 1301 0.885 0.46
Replicate 2 3802 1267 0.862 0.51
Residue 6 8821 1470

Table 4: Yield
Df Sum Sq Mean Sq value Pr(>F)
Treatment 3 56 28.2 0.246 0.79
Replicate 2 266 88.78 0.774 0.55
Residue 6 689 114.77

e. Work to be Completed.

Mathew’s lab will complete the DNA extraction directly from a total of 84 soil samples collected multiple times (Objective 1: 36 and Objective 2: 48) and subject them to the Fusarium and Pythium-specific qPCR assay to identify species of Fusarium and Pythium in the next six months.

f. Other relevant information: potential barriers to achieving objectives, risk mitigation strategies, or breakthroughs.

The trial for Objective 1 was lost due to hail damage in Carrington (hail was observed during the week of 07/21/2024); thus, the data collected from this trial is not reliable. The trial will be repeated in 2026.

g. Summary
The tillage practice and residue management trials did not demonstrate significant differences in stand count and yield among the treatments. This indicates a necessity for further research, particularly given that the tillage practice trials were adversely impacted by hail during the growing season, which substantially reduced the overall yield.

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Soybean is an important crop for ND farmers. From the 2023 survey for soybean diseases, we observed yield-limiting diseases caused by pathogens (e.g., Fusarium) that are known to survive in crop residues. At this time there is limited literature on whether tillage practices and residue management can affect the Fusarium population causing diseases in soybeans. Through this research, farmers will obtain information on how tillage practices and residue management can affect the development of Fusarium diseases.