Final report for GNC23-369
Project Information
Our project titled “Develop grower-appropriate plant residue management methods to reduce asparagus beetle damage” investigates sustainable agriculture management methods for a major pest of the Michigan asparagus industry, the common asparagus beetle. This beetle causes $1 million in economic losses annually for Michigan growers; 4% of crop value due to only one pest. To manage asparagus beetle populations during spear harvest, growers primarily rely on foliar insecticides with a 24-hour preharvest interval. These are sprayed frequently to remove adult beetles and deter eggs from spears that are picked daily for the fresh market. Reliance on insecticides is not sustainable and growers need alternative methods to suppress beetle populations during harvest. My research will target the overwintering stage of the asparagus beetle’s life cycle. Previous research in the MSU Vegetable Entomology Lab determined that adult asparagus beetles seek shelter mainly in asparagus residue in asparagus fields. My research project builds on this by examining the impact of various mowing methods and mow timing on asparagus beetle overwintering. The goal of this project is to create a sustainable, economical, and effective management method for asparagus beetles. I will establish a replicated trial in collaborating growers’ fields with four different mowing treatments. I will then evaluate overwintering asparagus beetle survival in the plant residue produced from these treatments using cage experiments and field observations. Learning how to manage plant residue to suppress beetle populations will reduce the number of insecticide applications and thereby costs of production. Outcomes will improve grower knowledge of integrated pest management, reduce input costs, and decrease pesticide residues. A decrease in insecticide use will promote environmental sustainability that generates better produce and healthier communities. To evaluate growers’ perceptions of plant residue management, I will conduct surveys and a focus group evaluation to better understand current management practices in addition to learning about viable avenues for incorporating new practices into crop management systems. From my research project, growers will learn that implementing residue management practices can lower asparagus beetle pressure. Growers who establish residue management practices in their asparagus production will increase their return on investment while decreasing asparagus beetle populations. By decreasing asparagus pest populations using sustainable agricultural practices, we can promote economic stability, healthy communities, and safer environmental practices in the asparagus industry.
From my project, growers will be able to learn about the importance of integrated pest management through the incorporation of cultural control methods in asparagus production. Growers will learn about how different mowing methods can control asparagus beetle populations prior to the harvest season. Growers will learn that there are economical and efficient means of controlling pest species besides utilizing pesticides. Additionally, my project will serve as an example of a successful cultural control method in vegetable production for extension specialists and related researchers.
In terms of action outcomes, growers will adjust their current asparagus beetle management from relying on insecticides to a cost-effective residue management practice. Presenting my findings at grower meetings and in publications will increase growers' awareness about new asparagus beetle management practices. I will measure these action outcomes by surveying and interviewing growers about their current asparagus beetle management practices, their willingness to alter their practices, if they have reduced insecticide applications, their economic perception of incorporating mowing as an asparagus beetle management practice, and their awareness of my project outcomes. My research project outcomes will establish sustainable asparagus beetle management practices among growers, and it will promote an economically viable cultural control method.
Research
Mowing Trial 1
To conduct our research project on how residue management affects asparagus beetle overwintering during 2023, our field site was mowed during the asparagus off-season in fall 2022 and spring 2023. A mature commercial asparagus field in Pentwater, MI (43°48'15"N 86°23'03"W) was selected as the primary research site based on grower engagement and a previous history of asparagus beetle pressure. An 8.5 acre section of the field was split into four 2 acre subsections, each representing one of the four mowing treatments. Our mowing treatments include mowing with a rotary mower twice in the fall (2fall), mowing with a rotary mower once in the fall and once in the spring (fall/spring), mowing with a rotary blade once in the fall and a flail mower once in the spring (fall/spring(flail)), and mowing with a rotary mower twice in the spring (2spring). Of the treatments, asparagus growers most commonly implement fall/spring mowing for residue management due. For this reason, fall/spring represents our grower standard and control for which we compare the performance of the other mowing treatments. 2spring was also included in our experiment based on its utilization by asparagus growers, but to a lesser extent than fall/spring. Treatments 2fall and fall/spring(flail) were introduced as novel mowing practices without prior use by growers. 2fall, like 2spring, limits mowing to one season, aiming to limit the amount of residue available to asparagus beetles by chopping it during the fall season. In contrast, fall/spring(flail) incorporates the use of a flail mower during the spring mowing. Unlike rotary mowers, which cut ferns horizontally and potentially creates stalks favorable for asparagus beetle overwintering, flail mowers feature vertically oriented blades. The integration of the flail mower into the treatment sought to prevent hollow stalks by halving ferns with the vertical blades. Treatments mowed in the fall were mowed on November 14, 2022 and treatments mowed in the spring were mowed on April 27, 2023. Residue was left in the field after mowing to simulate typical environmental conditions prior to use by overwintering beetles.
Field surveys
Prior to residue collection, we conducted several field surveys at our research site to determine the intensity of asparagus beetle pressure in the field. Surveys took place on August 9th and 15th, 2023, with a third survey scheduled for August 22nd that did not occur due to pesticide applications made to the field. For both dates we surveyed individual plants for the presence of asparagus beetles, recording the number of adults, eggs, and larvae found in each treatment. Plants (25) were selected randomly by walking about 10 paces apart within a treatment row, this was repeated two times per survey with a total of 100 plants per treatment. At each plant we recorded the number of each life stage we could see at eye-level on the asparagus fern along with the plant number, treatment, and date. Additional data was collected on August 15th on the residue found in the field. At each location surveyed, we estimated the percent of residue coverage and size within a square meter quadrat between the rows of asparagus to determine differences in residue coverage across the four treatments. For adult, egg, and larvae counts, we calculated the average number of each life stage per plant per mowing treatment. Each life stage was modeled using a generalized linear mixed-effects model (glmer function from the lme4 package) with date and plant as random effects fitted in a binomial distribution. Furthermore, we performed pairwise comparisons (emmeans function from emmeans package) across the four treatments and adjusted the p-values using a false discovery rate. Additionally, we analyzed the average percent of residue coverage found within each mowing treatment using a beta regression model and preformed pairwise comparisons with the ‘emmeans’ package.
Residue collection
On August 15th, 18th, and 22nd, 2023 residue was collected from each treatment subsection. Residue was collected by hand, using rakes to carefully separate residue from the soil and was placed into brown paper bags labeled with the corresponding treatment and date. Because of prior insecticide application, residue collected on August 22nd was labeled stating it was treated with carbaryl. Residue collected from this day was separated into its own set of overwintering cages from residue collected on the previous days to ensure no significant differences were seen between either group. The residue collected was transported back to East Lansing, MI and stored at 4 ± 2°C until cages were assembled.
Mowing Trial 2
To further determine if there were differences in the residue across our four treatments, we conducted another mowing trial in 2023-2024 at the Asparagus Research Station in Hart, MI. Mowing treatments were reproduced from the previous year, this time in a randomized complete block design of 45 feet by 30 feet plots in a mature asparagus field. Each treatment was replicated 4 times throughout the field, with 16 plots in total. Prior to residue collection, we recorded the number of residue pieces < 6 inches within a square meter quadrant placed randomly within a plot and replicated three times. On May 9th, 2024, 4 quadrants of residue were collected from each plot in a similar way from the previous year. Bagged residue was transported back to East Lansing and stored at 4 ± 2°C until processed. Each bag of residue was sorted by measuring pieces of residue and placing them into a corresponding size class container. Each class of residue was weighed (kg) and recorded for every bag to be analyzed.
The number of pieces >6 inches per each mowing treatment was analyzed using a generalized linear model with a poisson distribution. Treatment means were compared using the 'emmeans' package with Tukey's adjustment method. The residue classes weighed for each treatment were analyzed with a generalized mixed model with gamma distribution and date as a random factor. Treatment means were compared using the package ‘emmeans’, applying the false discovery rate adjustment method.
Overwintering cages
To test how our mowing treatments from our first mowing trial affect asparagus beetle overwintering, we utilized overwintering cages (0.5 m x 0.5 m x 0.1524 m) from previous research to contain a simulation of beetle overwintering during fall 2023 and winter 2024. Cages were constructed of untreated pine wood planks (15.24 cm x 2.54 cm) creating the frame, and aluminum window screening (60.96 cm x 30.48 cm x 0.0635 cm) covered the top of the cages to prevent beetles from escaping. Any damage from previous research and caused by prolonged storage was repaired before our experiment began.
We separated the residue collected into two groups, ‘non-carbaryl treated residue’ and ‘carbaryl-treated’ residue. For both groups we weighed out the residue for all four mowing treatments, calculating an average weight from each treatment. Non-carbaryl asparagus residue (1 kg) of one of the four mowing treatments was placed into an overwintering cage, each was replicated 8 times for a total of 32 cages. Carbaryl-treated residue (1.4 kg) of one of the four treatments was placed into each cage, each mowing treatment was replicated 4 times for a total of 16 cages. We assembled 48 cages, arranging the carbaryl-treated and untreated groups into a separate randomized complete block designs between two asparagus fields at the Michigan State Horticulture Farm, Holt, MI. Carbaryl-treated cages were arranged in a 4 by 4 block design in a grassy lane between asparagus fields and non-carbaryl treated cages were organized in a 4 cage by 8 cage block design.
Asparagus beetles were collected from a commercial field in Shelby, MI (43°34'56.9"N 86°24'26.3"W) and kept in the lab on freshly picked untreated asparagus from the Michigan State University Horticulture Farm. Beetles were transported to the field on August 25, 2023, where each cage received 20 adult asparagus beetles. Asparagus beetles were kept in cages by securing vinyl screen on the top and landscape fabric on the bottom of cages, allowing for natural water drainage throughout the winter. The window screening side faced up towards the sky to allow for air to circulate throughout the cages. All cages were left out in the field over the remaining fall and winter seasons until April 18th, 2024 when temperatures began to rise.
Emergence counts from overwintering cages
On April 18th, 2024, residue from overwintering cages was removed and placed into plastic bags labeled with the corresponding cage number and date. Residue bags were transported back to campus where bags were opened and placed into individual cages to allow for beetle emergence. Emergence cages were kept at 24 °C with 24 hours of ambient lighting to ensure overwintering beetles emerge. Emergence cages were checked every other day and emerging beetles were counted and recorded with the cage number, treatment number, residue group, and date every two days starting April 19th until May 21st. After data was recorded, beetles collected from the emergence cages were subsequently frozen to prevent double counts. The emerging beetle count data was analyzed with a generalized linear mixed model with a binomial distribution with mowing treatment as a fixed factor and date as a random factor. Our two residue groups, carbaryl and no carbaryl, were analyzed separately yet there was no difference of the individual groups compared to the combined emergence results. Treatment means were compared using ‘emmeans’ with the false discovery rate adjustment method.
Grower Surveys
We surveyed asparagus growers who attended the Oceana Asparagus Day on February 22nd, 2024. Asparagus growers who attended the meeting were asked to complete an electronic survey with several questions about their current asparagus beetle management, current residue management, and demographic information. Questions asked to growers included: “What best describes your role in the vegetable industry?”, “How frequently do you spray for asparagus beetles during harvest?”, “How many spray applications do you apply for beetles during harvest season?”, “How frequently do you spray for asparagus beetles during the fern season?”, “How satisfied are you with the level of asparagus beetle control you currently achieve?”, and “When do you typically mow asparagus fern?”. Several responses were available for growers to select and were recorded for each question using an electronic survey program.
Mowing Trial 1
Field surveys
Field surveys conducted in summer 2023 indicated differences in the average number of life stages across treatments. The 2fall mowing treatment had a significantly higher average of adult beetles (z= 4.496, p<.0001) compared to the other three treatments. Plants in the fall/spring(flail) and 2spring mowing treatments had a higher average of eggs (z=-3.092, p= 0.0060) compared to 2fall and fall/spring treatments. The 2spring mowing treatment had a significantly higher average number of larvae on the plants than all other treatments (z=-5.477, p <.0001), and 2fall and fall/spring(flail) treatments had a higher average number of larvae compared to fall/spring mowing treatment (z=3.682, p=0.0007). Treatments were similar in the average amount of residue found within a square meter (z=0.326, p=0.9880).
Percent residue
During our field surveys, we visually estimated the percentage of residue coverage and size of residue at every data point within a given mowing treatment. Using that data, we sought to determine differences in the composition of our mowing treatments residue. There was significantly more mixed residue in our fall/spring treatment compared to the 2spring treatment (z= 3.826, p= 0.0125). However, no other size class comparison between our treatments resulted in significant differences. Although there seems to be noticeable differences in our treatments based on the graph results, we can attribute the lack of significant values based on inadequate replication of the survey.
Grower survey
Responses from the grower survey were recorded using an electronic survey system which automatically calculated the percentage a response was selected. For our first question, “What best describes your role in the vegetable industry?” 58% responses indicated that attendees were established growers (>10 years experience) and 32% were beginner growers (<10 years experience). The remaining 10% of the responses indicated that attendees were affiliated with the industry but not growers. Our second question “How frequently do you have to spray for asparagus beetles during harvest?” 57% of attendees reported that they spray insecticides for the common asparagus beetle every year, while 40% responded they spray some years. Following that question, we asked attendees “How many sprays do you typically apply for beetles during harvest?” 76% of our participates responded that they make 1-2 applications, 21% responded with 3-4 applications, and the remaining 3% responded 2-3 applications. For our third question we asked “How frequently do you have to spray for asparagus beetle during the fern season (post-harvest)?” with 100% of our participates spraying for beetles every year post harvest. Next we asked growers “How satisfied are you with the level of asparagus beetle control you currently achieve?” Of the responses, 58% reported that they were somewhat satisfied with their current management and 39% were very satisfied. Only 3% of attendees were not satisfied with their management of the asparagus beetle. Our final question pertained to attendee’s mowing practices, asking “When do you typically mow asparagus fern?” 87% of participates responded that they mow once in the fall and once in the spring, 6% mow twice in the spring, and 6% use other mowing methods.
Mowing Trial 2
Residue characteristics
We conducted an additional experiment in 2023-2024 to determine characteristic differences between our mowing treatments. We first counted the number of pieces >6 inches to examine visible differences in our residue. Only one statistical difference was found between 2fall and 2spring, with 2fall having significantly more pieces >6 inches within its plots (z= 3.821, p= 0.008). The fall/spring and fall/spring(flail) treatments were statistically similar to 2fall (z= 2.238, p= 0.1131) and 2spring (z= 1.667, p= 0.3414) treatments. After our initial analysis, we sorted the residue collected from our field plots for a comprehensive analysis. Like our first mowing trials in 2022-23, there was few statistical differences in the composition of our mowing treatments. Fall/spring, fall/spring(flail), and 2spring had significantly more pieces >25cm compared to our 2fall treatment (z= 2.601, p= 0.0188). Yet of the 5 other size classes sorted, there was no other statistical differences found between the mowing treatments.
Emergence counts
Of the data collected on the emerging beetle counts from the overwintering trial, our analyses did not suggest any treatments suppressed beetle populations better than one another. We analyzed our emergence counts collectively and in their respective groups (carbaryl and no carbaryl). For the combined emergence counts, we found no significant differences in the average number of emerged beetles across treatments (z= 1.290, p= 0.4967). When separately analyzed by groups, neither carbaryl (z= 1.773, p= 0.2289) and no carbaryl (z= 1.773, p= 0.2289) groups showed any significant difference in the average number of emerged asparagus beetles. For all three analyses, we found that each treatment averaged less than one beetle per cage. However, we cannot confidently attribute the low emergence number to the effectiveness of our trials, as a mild winter in Michigan may have prevented beetle overwintering.
Educational & Outreach Activities
Participation Summary:
We shared our results with growers at the Great Lakes Expo, in the MSU E-Newsletter for agriculture, in extension presentations at fall field days organized at the asparagus research station, and at the Oceana Asparagus Day. We also shared our findings with growers in research and extension presentations in a meeting when British growers were visiting the Michigan asparagus industry.
Project Outcomes
Our project contributes to decreasing the need for pesticide applications. This will be achieved through more effective management of asparagus residue, which is the place where asparagus beetles overwinter. By reducing large residue pieces through mowing, beetle mortality will increase during the winter and there will be fewer beetles to damage the crop the following year.
We learned more about growers' perceptions of sustainable agriculture. Growers are motivated to try new methods and better understand the usefulness of currently deployed methods in order to make their pest management more economical and successful.