Sustainable pest management for Alfalfa mosaic virus in chile peppers in organic and conventional production

The research objectives of this project are to 1) investigate the effect of host plant resistance and consumptive and non-consumptive effects of predators on lowering AMV incidence and severity in organic and conventional fields; and 2) develop outreach and education programming to increase awareness of best management practices for AMV in chile peppers.  Research will be conducted in producers’ fields and at the Colorado State University Agricultural Research, Development, and Education Center (ARDEC). Mass releases of biological control agents combined with host plant resistance will be evaluated on two pepper farms in Pueblo, Colorado. The combination of host plant resistance and biological control on organic and conventional fields will be evaluated at ARDEC. The goal of these objectives is to quantify the benefit of using resistant varieties of peppers with and without releases of generalist predators in organic and conventional chile pepper fields, and to formulate management recommendations for farmers based on our findings.

Objective 1: Investigate the effect of host plant resistance and consumptive and non-consumptive effects of predators on lowering AMV incidence and severity in organic and conventional field:

Host plant resistance will be conducted at DiSanti Farms in Pueblo Colorado over the 2024, 2025, and 2026 growing season and the combination of host plant resistance and biological control will be conducted at Colorado State University’s Agricultural Research, Development, and Education Center (ARDEC) over two growing seasons in 2025 and 2026. Each growing season will start in mid-May and end in late September. DiSanti Farms is a family owned and operated farm. Two farms will be used in this project to evaluate host plant resistance on AMV infection and severity. ARDEC will provide organic and conventional fields to evaluate the combination of host plant resistance and biological control in two different cropping systems.

To investigate the effect of host plant resistance and predator effects on lowering AMV incidence and severity, a split-plot design will be implemented. Production system (organic, conventional) will be the whole plot factor, biological control will be the split-plot factor, and host plant resistance will be the split-split-plot factor. The chile pepper cultivars that will be used are ‘Masivo’ and ‘Joe Parker’. ‘Masivo’ is a cultivar that is grown by producers and has shown promising results in the field already. ‘Numex Joe Parker’ represents the broad class of New Mexico type long green chiles and is susceptible to AMV. The split-plot factor will consist of releasing minute pirate bugs, Orius insidiosus (Hemiptera: Anthocoridae), a known natural enemy of thrips and aphids. Each of these treatments will be replicated seven times, and each replicate will consist of ten plants. To account for the possible movement of minute pirate bugs from treatment plants, we will establish a 15-foot buffer space planted with corn (var. ‘Silver Queen’) to reduce the risk of spillover. To implement the biological control treatment, one to four minute pirate bugs (Kawai, 1994; Dumont et al., 2023) will be released on each plant depending on the plant size. Releases will take place for two consecutive weeks in mid-May. Plants will be inspected for predators following the releases and if none are found, additional minute pirate bugs will be released. To better understand the timing of aphid movement into pepper fields, pan traps will be placed in between rows starting in mid-May and continuing until the second week of June. We predict that the increased presence of natural enemies in treatment plots will threaten and deter aphids from transmitting AMV, resulting in decreased incidence and severity.

To assess AMV incidence, leaves from five plants in each replicate will be collected and brought back to the laboratory to determine AMV presence through enzyme-linked immunosorbent assays (ELISAs), resulting in OD (optical density) values. Leaves will be collected and analyzed two times throughout the growing season (once in mid-May and again in late July). To measure AMV severity, data will be collected on the estimated proportion of symptomatic leaves per plant, as well as overall fruit quality and yield data. Yield data will be collected at the end of each growing season. Fruit will be collected weekly after the peppers reach red-mature stage defined as 50% or more of the fruit turning red in color. Parameters measured for each pepper will be mass, length, and presence/absence of AMV symptoms. Analyses of variance (ANOVA) (R Core Team 2023) will be used to assess the effects of plant variety and predator releases on the percent of symptomatic leaves symptoms per plant, OD values (i.e., AMV titers), and yield. Means separation tests (Tukey’s Honestly Significant Differences test) will be performed where appropriate. Logistic regression will be used to assess whether the incidence rate of AMV (i.e., number of symptomatic plants divided by the total number of plants used in the experiment) is affected by host plant resistance and biological control in organic and conventional fields.

 To investigate host plant resistance in a more applied setting, DiSanti Family commercial chile pepper farms in Pueblo, CO will be used. Disease severity and incidence will be collected as previously described. 

Plan for objective 2: Develop outreach and education programming to increase awareness of best management practices for AMV in chile peppers.  

The overall educational objective for this project is to the develop outreach and educational programming to increase the awareness of best management practices for AMV in chile peppers. The goal of this objective is to 1) facilitate peer-to-peer education among chile pepper producers through field days hosted in locations where the research will be conducted, 2) create a factsheet for management of AMV in peppers in Colorado, and 3) communicate findings with peers through peer-reviewed publications.

To facilitate peer-to-peer education, we plan to host an annual field day each year of project. This field day will take place at the Arkansas Valley Research Center in Rocky Ford, Colorado, the closest research station to Pueblo, Colorado. A survey will be distributed to attendees to evaluate how they currently manage the vector and disease, and to voice their top concerns based on the previous growing season. Surveys will be issued during the following two growing seasons for comparison of management practices, and to measure any changes in tactics used and developing concerns amongst producers. The two field days that will be held in August of 2025 and August of 2026 will provide a space to communicate with farmers on the progress of the project, any patterns that we see in the system, and to communicate any adjustments made based on the previous growing season. Annual survey data and field day reports will be written and disseminated to collaborating producers after each growing season.

A factsheet with management recommendations will be created and housed on the Colorado State University Center for Sustainable Pest Management website (https://agsci.colostate.edu/agbio/ipm/). This webpage will include information about the vector and virus, the impact it has had on chile pepper production in the country and specifically in Colorado, and recommendations supported by this research. The webpage will be created at the end of the last growing season (Fall 2026).

References

Dumont, F., Solà, M., Provost, C., et al. (2023). The potential of Nabis americoferus and Orius insidiosus as biological control agents of Lygus lineolaris in strawberry fields. Insects, 14(4): 385.

Kawai, A. (1994). Control of Thrips palmi Karny (Thysanoptera: Thripidae) by Orius spp. (Heteroptera: Anthocoridae) on greenhouse eggplant. Applied Entomology and Zoology, 30(1): 1-7.