Progress report for GNC24-395
Project Information
Non-chemical pest management offers a variety of positive impacts on specialty crop production. In the Midwest, especially Ohio, where pepper production is economically significant and faces multiple pest threats, of which thrips are a prominent one, exploring alternative management methods is crucial. Current thrips management relies heavily on calendarized insecticide programs leading to excessive usage, fostering insecticide resistance, and raising production costs. Insect natural enemies provide a biological control alternative for managing insect pests in agricultural ecosystems. To date, beneficial organisms are frequently undervalued within pepper production, and, like the targeted pests, they are directly impacted by calendarized insecticide programs, causing a decline in their natural populations within the agroecosystem (Srivastava et al., 2014).
Previous research has identified that Integrated Pest Management (IPM) approaches, such as threshold-based insecticide applications, the integration of differently colored plastic mulches, and reduced fertility rates offer alternatives for thrips management compared to calendar-based insecticide programs. Thus, we propose to examine the impact of these management practices in a factorial experiment. We will examine the combined effect of different insecticide programs (weekly, threshold-based, untreated control) paired with different mulch types (reflective, black, and bare ground) and fertility regimes (grower fertilizer program, sufficiency-based fertilizer program, and an unfertilized control) first in a controlled trial and then followed by on-farm replications to evaluate most effective treatment combinations under more realistic production conditions.
The results of our study will be used to develop an IPM program that provides effective alternatives for controlling thrips in peppers. This program will reduce the dependence on insecticide, thereby promoting the natural enemy community responsible for natural pest control. We also anticipate reducing fertilizer rates which will slow pest populations and reduce fertility-associated pollution. The proposed IPM program is expected to help growers save on production costs, slow the onset of insecticide resistance, and promote more resilient agroecosystems better equipped to combat pest through synergies with other IPM tactics like biological control. Additionally, 3-D extension models and fact sheets will enhance grower’s abilities to identify thrips and the natural enemies associated with their biological control aimed at expanding their knowledge of these biological systems to encourage their conservation. We plan to disseminate the project's findings in the Northcentral region through presentations at grower/scientific conferences, as well as creating content for agricultural extension.
References:
M. Srivastava, et al. Fla. Entomol. 97(2), 337-348 (2014)
United States. U.S. National Agricultural Statistics Service. https://www.nas.usda.gov/ (2022)
- Evaluate the impact of combining different insecticide programs, fertility regimes, and plastic mulch types on:
- thrips densities, and marketable yield and
- natural enemy abundance
- Collaborate with regional pepper growers to apply best alternative pest management practices on-farm to improve production outcomes.
- Develop 3-D printed models to enhance extension material and disseminate research findings to Pepper stakeholder groups.
Research
The Year 1 field experiment was conducted at the North Central Agricultural Research Center in Fremont, Ohio.
Experimental Design
The study evaluated the interaction of: a. Insecticide program (weekly calendar-based spray vs. untreated control), b. Mulch type (black polyethylene mulch, diamond reflective mulch, bare soil) and, c. Fertility regime (high NPK, sufficiency-based NPK, unfertilized control).
Due to low thrips pressure in year 1 of the study, the threshold-based insecticide treatment, which originally meant to be evaluated, could not be implemented, as thrips densities never exceeded the economic threshold (6 thrips per flower). The final Year 1 experiment was conducted as a 2 X 3 x 3 factorial design arranged in a randomized complete block design with four replications resulting in 72 plots.
Each plot measured approximately 25 ft X 5 ft and contained 25 jalapeño plants.
Insecticide Treatments
Weekly insecticide applications were initiated at week 4 after transplant (which coincided with thrips infestation) and continued through week 12 for the calendar-based treatment. Untreated plots received no insecticide applications.
Mulch Treatments
-Black polyethylene plastic mulch (Poly Mulch, 2 mil thickness, 1.22 m wide, Farm Plastic Supply, Addison, IL).
-Diamond reflective mulch (96% reflective index, 100% light tight, 6 mil thick, 1.22 m wide, HTG Supply, Callery, PA).
-Bare soil as the no-mulch control.
Fertility Treatments
Fertility regimes were established based on pre-season soil testing:
-High NPK (grower-standard program exceeding recommended sufficiency levels by 1.5X)
-Sufficiency-based NPK (Midwest Vegetable Production Guide recommendations and Spectrum Analytic Inc recommendations per initial soil test results)
-Unfertilized control
Data Collection
Thrips assessments: Weekly thrips scouting was conducted beginning four weeks after transplant and continued for eight consecutive weeks. Two fully opened flowers and upper canopy leaves were sampled from 10 plants per plot. Adult and larval thrips were counted visually.
Natural enemy assessments: Populations of key natural enemies were monitored using yellow sticky cards (12.7 X 17.8 cm, ARBICO Organics®). One sticky card was placed at the center of each plot on a bamboo stake positioned at plant canopy height. Sticky cards were replaced every two weeks, with each exposed side representing one week of sampling. Cards were collected, wrapped to prevent contamination, stored at -20°C, and later examined under a stereomicroscope. Primary natural enemies recorded included: a. Minute pirate bugs (Anthocoridae), b. Lady beetles (Coccinellidae) and, c. Lacewings (Chrysopidae and Hemerobiidae)
Plant health metrics and yield assessment: Plant growth was monitored/measured twice during the growing season at two key crop developmental stages representing pre-bloom and post-bloom periods. Within each plot, five plants were randomly selected from the innermost 20 plants to avoid edge effects. Height was measured from the soil surface at the stem base to the apical meristem.
Leaf chlorophyll content was also assessed twice during the season at corresponding developmental stages. Five plants per plot were randomly selected from the 20 innermost plants. From each selected plant, two fully expanded and mature leaves from the upper canopy and from different stem branches were measured using a handheld chlorophyll concentration meter (MC-100, Apogee Instruments, North Logan, UT). The two readings were averaged to represent chlorophyll content per plant. Chlorophyll measurements were used as an indicator of plant nutritional status and vegetative vigor under different fertility and mulch treatments.
Following final harvest, soil samples were collected to evaluate treatment-level differences in nutrient availability. Six soil cores were collected from each plot, composited into a single sample per plot, and submitted for nitrogen (N), phosphorus (P), and potassium (K) analysis to a commercial soil testing laboratory (Spectrum Analytic Inc, Washington Court House, OH). Soil nutrient analysis was used to verify separation among fertility treatments and assess residual nutrient levels following the growing season.
Peppers were harvested between September 5 and September 26. Fruits were graded according to USDA market standards for non-sweet peppers.
For each plot, the following were recorded: a. Total fruit number, b. Number of marketable fruit, c. Total marketable fruit weight, d. Number of fruit exhibiting bronzing caused by thrips feeding
Bronzing was defined as cosmetic scarring affecting more than 5% of the fruit surface. The proportion of damaged fruit relative to total harvested fruit was calculated as an indicator of thrips-related injury.
Statistical Analysis
All analyses were conducted using R statistical software. Treatment effects of insecticide program, mulch type, fertility regime, and their interactions were evaluated using mixed-effects models. Block was included as a random effect to account for spatial variability in the field. Linear mixed models were used for plant height, chlorophyll concentration, yield, and proportion of damaged fruit. Generalized linear mixed models were used when response variables required non-normal error structures. Seasonal averages were calculated for thrips densities and natural enemy captures. Model assumptions were evaluated using residual diagnostics, and significant treatment effects were followed by pairwise comparisons with Tukey-adjusted tests at α = 0.05.
Soil Nutrient Status
Soil nutrient concentrations differed predictably among fertility treatments, confirming successful separation among high NPK, sufficiency-based NPK, and unfertilized plots. This indicates that fertility treatments were implemented effectively and maintained throughout the season.
Plant Height
Plant height was influenced by the interaction between mulch type and fertility regime. Under black plastic and diamond-reflective mulch, plants receiving sufficient or high NPK were generally taller than unfertilized plants. Across fertility levels, plants grown under plastic mulches were consistently taller than those grown under bare soil.
These findings suggest that mulch-mediated microclimate and fertility inputs interact to influence vegetative growth.
Leaf Chlorophyll
Leaf chlorophyll concentration was strongly influenced by mulch and fertility as independent factors. Plants grown under black plastic and diamond-reflective mulches exhibited higher chlorophyll concentrations compared to bare soil. Fertilized plants (high and sufficient NPK) had substantially greater chlorophyll concentrations than unfertilized plants.
No insecticide effects or significant three-way interactions were detected for chlorophyll.
Chlorophyll measurements indicate that fertility and mulch management directly influenced plant vigor and nutritional status during year 1.
Western Flower Thrips Densities
Thrips densities differed among insecticide treatments, mulch types, and fertility regimes.
Plots receiving weekly insecticide applications had lower thrips densities compared to untreated plots. Across mulch treatments, black mulch supported higher thrips densities relative to diamond-reflective mulch and bare soil. Fertilized plots supported moderately higher thrips densities compared to unfertilized plots. Although treatment effects were measurable, overall thrips pressure during year 1 season was low and did not reach economic threshold levels. As a result, Year 1 results should be interpreted cautiously and validated under potentially higher pest pressure conditions in Year 2.
Natural Enemy Densities on Sticky Card Captures
Sticky card captures showed varying responses among natural enemy taxa.
Minute pirate bugs and lacewings were not strongly influenced by treatment factors during year 1. Lady beetle captures varied among mulch types and insecticide treatments. Bare soil plots generally supported higher lady beetle captures, while diamond-reflective mulch supported fewer captures. Overall, natural enemy responses appeared more closely associated with habitat conditions (mulch type and plant vigor) than with insecticide treatment under low thrips pressure.
Yield and Fruit Quality
Marketable yield varied among treatment combinations and was strongly influenced by mulch type. Across fertility and insecticide programs, diamond-reflective mulch consistently produced the highest marketable yield, exceeding yields under bare soil by approximately 60%. Black mulch produced intermediate yields.
Fruit bronzing caused by thrips feeding differed among mulch treatments, with diamond-reflective mulch associated with lower proportions of damaged fruit compared to bare soil. While these results indicate promising treatment combinations, multi-year data are necessary to determine consistency of yield responses under varying pest and environmental conditions.
Educational & Outreach Activities
Participation summary:
Year 1 findings were widely disseminated through regional grower meetings, state and regional commodity conferences, and national scientific forums.
Across all outreach venues, approximately 190 farmers, 10 agricultural service providers, and 250 additional participants (including academic scientists, graduate students, industry representatives, and extension professionals) were reached.
Grower-focused presentations were delivered at the Muck School Grower Meeting (January), the Ohio Produce Growers and Marketers Association (OPGMA) meeting, and the Greenstar Grower Cooperative Annual Meeting in Canfield, Ohio. These presentations emphasized practical implications of fertility optimization, reflective mulch adoption, and risk reduction strategies in pest management.
In addition to in-person presentations, a newsletter article summarizing preliminary Year 1 results was published through Vegetable Growers News, extending outreach beyond meeting attendees and increasing awareness among vegetable producers across the region.
Scientific presentations were delivered at the Ohio Valley Entomological Society Association (OVEA), and the Entomological Society of America (ESA) regional and national meetings. These presentations expanded the scientific visibility of the project and strengthened collaborative engagement within the research community.
In addition to oral presentations, multiple scientific posters showcasing Year 1 results were presented at:
-Great Lakes Fruit and Vegetable Expo (GLEXPO)
-The College of Food, Agricultural, and Environmental Sciences (CFAES) Annual Plant Science Symposium at The Ohio State University
-The North Central Branch Meeting of the Entomological Society of America
-The DeLong Student Competition within the Department of Entomology
Approximately 50 printed brochures summarizing preliminary Year 1 findings were distributed during extension events. Informal consultations frequently followed presentations, allowing growers to discuss potential implementation of sufficiency-based fertility programs and reflective mulch systems within their own operations.
Project Outcomes
Year 1 findings suggest potential benefits for sustainability in multiple dimensions.
Economic
Reflective mulch combined with sufficiency-based fertility maintained strong yield performance. Input optimization may reduce unnecessary fertilizer use and mitigate financial risk associated with preventive insecticide applications.
Environmental
Reduced fertilizer inputs may decrease nutrient runoff risk. Habitat-mediated influences on natural enemies suggest that agronomic practices can contribute to biological control conservation.
Social
Grower engagement increased awareness of systems-based IPM approaches that balance productivity and environmental stewardship. Continued outreach in Year 2 will evaluate behavioral adoption more formally.
Because year 1 represented a low-thrips year, year 2 replication is essential before drawing definitive conclusions regarding pest suppression efficacy.
Year 1 results reinforced the importance of evaluating pest management within a systems framework. Strong mulch X fertility effects on plant vigor and pest dynamics highlight the complexity of crop-pest-environment interactions.
Unexpectedly, natural enemy abundance appeared more influenced by habitat and plant vigor than insecticide treatment under low pest pressure conditions. This improved our understanding of ecological drivers of biological control in specialty crops.
The need to adapt experimental design due to low thrips pressure strengthened our capacity for flexible and realistic field research in IPM systems.
Multi-year evaluation is critical to account for variability in pest pressure. Future work should further explore the mechanisms by which mulch and fertility influence natural enemy dynamics.
Year 2 on-farm validation trials will be essential to assess scalability and adoption potential under commercial production conditions.