Improving two spotted spider mite management in high tunnel cucumber production

Progress report for LNC20-438

Project Type: Research and Education
Funds awarded in 2020: $249,919.00
Projected End Date: 12/31/2023
Grant Recipient: Purdue University
Region: North Central
State: Indiana
Project Coordinator:
Dr. Laura Ingwell
Purdue University
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Project Information

Summary:

The work proposed here, entitled “Improving two-spotted spider mite management in high tunnel cucumber production” is broadly aimed at increasing the economic viability of crop diversification in high tunnel systems. High tunnels (HT) are a popular tool that increase the growing season in temperate climates and offer protection from environmental stressors, such as frost and excessive rain. High tunnels have been increasing in use across the US, in part due to the NRCS-EQIP program that offers financial assistance towards the investment in these structures. Some of the most economically viable crops currently grown in high tunnels include tomatoes, leafy greens and increasingly cucumbers; tomatoes are currently the dominant crop with little or no crop rotation. Furthermore, there are pest and disease challenges associated with high tunnels that need more effective, sustainable management strategies specifically developed for these production systems. Some of the pest and disease challenges also limit crop rotation. For cucumber production, exclusion-screening tactics were developed by Project Coordinator-Ingwell as a strategy to manage one of the most important pests: cucumber beetles and the bacterial pathogen they transmit. Two-spotted spider mites (TSSM) are the other major challenge because they are difficult to detect and monitor and there are few miticides available for high tunnel systems, none of which are permitted in certified organic production. The aim of this project is to develop an integrated pest management plan that minimizes the impacts of TSSM on cucumber, thus increasing the viability of producing cucumbers in HT. We aim to provide cultural and biological strategies including selection of more tolerant cultivars and the application of soil amendments to increase tolerance, develop an effective and easy to adopt scouting protocol, and establish recommendations based on the optimization of commercially available TSSM natural enemies for biological pest suppression. We will also evaluate the efficacy of biopesticides and application methods as an additional management strategy, recognizing that cultural and biological control may not be effective or appropriate in all situations. Relevance will be ensured by engaging with farmers and conducting on-farm research. We will disseminate information to farmers through demonstrations, print, and digital Extension media.

Project Objectives:

Learning outcomes:

Increased 1) understanding of pest susceptibility among cucumber cultivars and in relation to soil amendments; 2) farmer ability to detect and monitor TSSM; and improved 3) knowledge to implement biological control; 4) understanding of the efficacy of biopesticides in HTs.

Action outcomes:

HT farmers 1) select cucumber varieties less susceptible to TSSM; 2) apply soil amendments to reduce crop susceptibility; 3) scout for TSSM and train employees to do so; 4) implement biological control.

System outcomes:

Cucumber production in HTs becomes more economically viable, increases crop diversity and results in greater resiliency and viability of local food systems.

Introduction:

Within the context of food production, the attitudes and preferences of consumers often drive production practices. The demand for local and organic produce has supported growing networks of small, diversified farmers in communities throughout the United States. The North-Central region is no exception. To keep up with the demand many farmers are investing in season extension tools, such as high tunnels, which provide fresh local produce longer in temperate climates. High tunnels (HTs) are also proving to be a very important tool to combat a changing climate, offering protection from unpredictable precipitation, wind and frost. In the Midwest region, HT systems have become a widely adopted production practice on small and urban/peri-urban farms. In Indiana alone, close to 300 HTs have been constructed through the NRCS-EQIP grant since 2012 (NRCS 2017). This number does not account for those installed without the assistance program, therefore representing an underestimate. Farmers with HT production report improved farm economic stability and increased crop yields (Bruce et al. 2017). Other benefits like early yield, extended season and higher quality help producers strengthen local sales (Bruce et al. 2019a,b).

Arthropod pest management is one of the most stressful constraints; especially in high tunnels where less production experience and science-based pest management information is available and where the main pests are often different from those found in the field. Some pests are difficult to detect at low levels, but their symptoms are often diagnostic. Others are detectable but exert much higher damage than that experienced in open field production (Ingwell et al. 2017). Management tactics need to be tailored to the unique nature of HT production systems. Efficacy of traditional strategies may not translate to HTs. There is a need for integrated pest management recommendations developed and designed for HT systems. These recommendations need to be effective and provide diverse strategies with predictable results, empowering farmers to make informed decisions. For organic farmers in particular, there is not enough information about the efficacy of OMRI-approved pesticides and successful biological control for HT systems. Furthermore, there is a lack of understanding about the potential for development of pest resistance to biopesticides (Ingwell, personal communication). Resistance among many of the common HT pests can manifest as behavioral (avoidance) or physiological (detoxification) and therefore may develop in response to any kind of control strategy: cultural, organic or conventional. One goal of our project is to increase scientific understanding of the efficacy of biopesticides in HT systems, a timely and important knowledge gap reducing farmer success of pest management.

Soil health management is another constraint for farmers in HT systems. The intensity of production, often 10 months of the year, rarely allows for a fallow or recovery period. One way farmers can deal with this high-intensity production is through the addition of organic matter to the soil. Research at Purdue University by Hoagland has shown that organic fertility amendments can improve soil quality in HT systems, specifically using green manure of hairy vetch and dehydrated alfalfa meal (Rudisill et al. 2015), and these soils are more disease suppressive (Hoagland et al. 2017). There is still much work to be done in terms of farmer education about soil health management and the selection of soil amendments that are most beneficial to each system. For instance, previous studies have demonstrated relationships between soil nutrient availability, plant health and damage by herbivores (Altieri and Nicholls 2003, Rowen et al. 2019). Here, we aim to understand the role that one amendment, vermicompost, has on the relationship between soil health and plant tolerance to TSSM.

The investment costs into HT structures and benefits of growing through the extended season exhibits a high economic stress on what is grown within them. Fresh market tomatoes are the most popular high tunnel crop and represent a key economic commodity for diversified vegetable growers, securing a price premium for early- and late-season product. Due to the popularity and economic benefit, Indiana high tunnel growers have historically grown repeated tomato plantings in these structures, with little to no rotation. Resulting from these practices, growers are beginning to experience challenges related to soil health, the accumulation of soil borne disease and insect pests.

Farmers recognize the need to diversify and optimize production and move away from the traditional cash crop of tomatoes to alleviate these challenges and break the pest cycles (Bruce et al. 2019b). The search for an economically competitive crop that is desired by the market and can be produced during the extended season provided by HTs has been challenging. In addition to leafy greens, cucumbers are emerging as a profitable crop well suited for HT production (Maynard, unpublished). Cucumbers are trellised vertically to take advantage of the space available for production, have been bred for protected cultivation, and can be produced to provide product early and late to extend the season for market farmers. Research on cucumber production in HTs has been progressing rapidly; the proposed research here is timely and will contribute to the remaining needs of HT cucumber challenges.

In a previously funded SARE project, Improving Seedless Cucumber Production to Diversify High Tunnel Crops (LNC17-390), we identified varieties that are well suited for HTs, growing techniques to optimize yield, and some of the most prevalent insect and disease challenges (Ingwell and Kaplan 2019, Guan et al. 2019). However, Guan and collaborating farmers identified two-spotted spider mites (TSSM) as the single most important obstacle to viable production today. The main impact is the reduction in the length of the season when spider mite infestations cause production to be terminated. Economic losses have been detected as early as four weeks after infestation in glasshouse cucumbers (Park and Lee 2005). This threatens to limit the adoption of cucumbers as a HT crop. Through conversations with a diverse array of market farmers in the state of Indiana team members have been able to gauge current practices allowing us to identify likely avenues for reducing losses from TSSM, which we will address in this project. The work proposed here builds directly from the current momentum towards cucumber production in HTs to address the important challenges of TSSM. We will provide a variety of management tools to aid in the control of spider mite pests specifically designed for production in high tunnels. Some of these recommendations (monitoring protocol and soil amendments) will be transferable to other crops grown in high tunnels that are susceptible to TSSM (including tomato, the most commonly produced HT crop in IN (Bruce et al. 2019a), as well as field-produced cucumbers, where applicable.

The long-term goal of this collaborative and interdisciplinary project is to increase our understanding of two-spotted spider mite dynamics and management in high tunnel cucumber production systems, thus increasing the economic viability and production of high tunnels. Our overall objective is to develop a comprehensive integrated pest management plan for TSSM including cultivar selection, soil amendment application to increase plant tolerance, monitoring, biological and chemical control recommendations developed specifically for Midwest high tunnel production systems. This project builds off the previous work on high tunnel production of cucumbers, funded largely by NCR-SARE (LNC17-390) and USDA-NIFA (Grant 2016-67012-24719/project accession no. 1007989). It comes at a time where there is a great need and recognition among high tunnel farmers for diversification, integrating economically viable crop types instead of or in addition to tomatoes.

Research

Hypothesis:

Objective 1: Evaluate varietal susceptibility and the capacity of soil amendments to increase the tolerance of cucumbers to TSSM.

Hypothesis: Cucumber cultivars differ in their susceptibility to two-spotted spider mites.

Objective 2: Develop a monitoring plan to improve TSSM management in HT cucumbers.

Hypothesis: Prediction of the spatial distribution within the high tunnel crop can increase the efficiency of early detection of two-spotted spider mites.

Objective 3: Develop recommendations for TSSM control using commercially available natural enemies and selected biopesticides.

H1: Predatory mites differ in their ability to control TSSM in high tunnel growing systems.

H2:Biopesticide efficacy differs in the control of TSSM as a result of the environmental conditions and population densities when they are applied.

Materials and methods:

This project includes a combination of field research conducted at three Purdue Agriculture Centers (PPAC, SWPAC, Meigs) spanning the latitudinal gradient of IN and on-farm with participating farmers to evaluate the implementation and efficacy of recommendations stemming from research findings. Knowledge gained will be extended to farmers, their advisors, and scientists through educational events, publications, and videos.

At the onset we will form an advisory panel of farmers, including Nate Parks, Genesis McKiernan-Allen, and Bud Vogt. The panel will provide suggestions for varieties, scouting protocols and biopesticide products and be the first to evaluate the resulting recommendations.

Objective #1: Evaluate varietal susceptibility and the capacity of soil amendments to increase the tolerance of cucumbers to TSSM.

Our goal is to develop preventative strategies to reduce the risks that TSSM impart on HT cucumbers. Our hypothesis is that by reducing crop susceptibility to TSSM, the incidence and need for intervention later in the growing season will be reduced. The rationale is that when the risk for infestation is lower, farmers can cultivate a crop that is less susceptible and requires less intervention later in the season.

1.1 Evaluate seedless cucumber varieties for tolerance to TSSM.

In previous work (LNC17-390) we identified Japanese-type cultivars more tolerant to TSSM (Guan et al. 2019). We will expand the cultivar evaluation to include at least 10 additional varieties beyond the previous work. This is crucial for growers, as the information is not available from seed companies.

Variety trials will be carried out in years one and two at SWPAC, PPAC and Meigs. Co-PIs Guan, Maynard, and Langenhoven will oversee the trials; Ingwell and the graduate student will measure TSSM incidence and evaluate susceptibility. Varieties will be planted in one HT at each farm in a randomized complete block design. Plants will be vertically trellised using the one-leader method which reduces the spread of TSSM between plants (Guan, personal observation).

TSSM tolerance (ability of plants to yield in spite of pest presence) will be monitored by counting the number of mites on each of three leaves taken from the bottom, middle and top on one plant from each variety within each row weekly. Leaves will be destructively sampled and returned to the lab for mite quantification. TSSM will be monitored throughout the growing season with no intervention and yield will be tracked. This method has been implemented and successful (Guan and Ingwell, unpublished). TSSM population dynamics, length of harvest and total yield will be evaluated to score tolerance of each variety. One row in each high tunnel will be treated with a miticide to maintain a set of negative control plants to evaluate potential yield losses to TSSM.

Results from this work and previous variety evaluations will be recorded in a database we will maintain online (https://extension.entm.purdue.edu/veg/) and make available through the Veg Crops Hotline. This resource will be offered to farmers and seed companies to increase the accessibility of cultivar tolerance to arthropod pests, which is difficult to find. The protocol used to measure tolerance will be posted so others may replicate and add to the information.   

1.2 Examine the impact of vermicompost and vermicompost tea amendments to increase tolerance of cucumber plants to TSSM.

There is accumulating evidence that biological soil amendments can inversely decrease development rates, increase mortality for arthropod pests (Razmjou et al. 2011, Arancon et a. 2005) and reduce damage by TSSM in particular (Edwards et al. 2010). The goal here is to explore the impact of vermicompost amendments on TSSM populations in HT cucumbers. Using the variety Corinto, we will evaluate the impact of two rates of vermicompost and vermicompost tea additions to cucumber plants in two HTs at Meigs in year one. Plants will be inoculated with TSSM from a lab-reared colony to ensure equal infestations across the soil treatments. We will quantify biological soil characteristics, TSSM population dynamics as described above and yield parameters. Hoagland and the graduate student will lead this effort.

Objective #2: Develop a monitoring plan to improve TSSM management in HT cucumbers.

TSSM are difficult to manage because their size makes them hard to find. They often go unnoticed until plant symptoms (chlorotic spots or webbing) appear. Our goal is to understand the spatial distribution and reproductive rates of TSSM in HTs to increase a farmers’ ability to detect and manage this pest. Our hypothesis is that by comparing binomial and enumerative sampling methods we will be able to develop a predictive and implementable TSSM monitoring protocol for farmers. The rationale is that increasing the ability of farmers to detect and monitor TSSM will lead to more timely and effective pest management decisions and increase adoption of HT cucumber production.

Our methodology will follow protocols found in Wilson et al. (1983), Raworth (1986), and Hepworth and MacFarlane (1992). The novelty of HT cucumber production is the environmental protection of the tunnel and the intensive growth and management to optimize production. Vertical structural complexity, accelerated growth and quick turn-over of plant material make it impossible to translate monitoring recommendations directly from other systems.

We will grow Corinto var. in two HTs at Meigs in year one. We will implement sampling methods across time and vertical space/age of the plant. Sampling methods include examining individual leaves with a hand lens (presence/absence and number) compared with counts from leaves collected and evaluated in the lab to get accurate estimates of TSSM populations and determine adjustments between protocols. Mite populations will not be treated with pesticides to understand the growth rate, with-in plant and with-in HT distribution and impact of intensive pruning and harvesting on TSSM dynamics.

Regression will identify the most reliable sampling method for farmers to implement, including measures of accuracy and precision (Iwao 1968, Ruesink 1980). We will measure time to conduct surveys and ease of training others to evaluate the economics of adoption. In years two-three collaborating farmers will implement and evaluate the sampling plan. Ingwell, Yaninek and the graduate student will lead this effort.

Objective #3: Develop recommendations for TSSM control using commercially available natural enemies and selected biopesticides.

Our goal is to identify the most efficacious and cost-effective methods to control TSSM.

3.1 Examine the efficacy of predatory mites for biological control of TSSM in HTs.

Natural enemies are used successfully in greenhouses to manage TSSM. Environmental constraints in high tunnels introduce challenges, such as emigration and variable temperature and humidity (Ingwell et al. 2018). Some of the most important factors to consider when implementing biological control include prey densities, plant architecture and environmental conditions. We hypothesize that depending on the time of year and plant development, pest suppression by natural enemies will vary depending on species. We will examine release rates, predator persistence and prey suppression to develop recommendations based on plant size, environmental conditions and level of infestation. The commercially available predatory mites in Table 1 will be evaluated.

Predator Species 

Generalist or Specialist 

Ideal Temp. (°F) 

Ideal Relative Humidity (%) 

Amblyseius andersoni 

Generalist 

42-100 

High at higher temps. 

Amblyseius cucumeris 

Specialist on thrips, will eat mites

66-80 

65-72 

Neoseiulus californicus 

Generalist 

50-105 

40-60 

Neoseiulus fallacis 

Specialist on mites 

Above 64 

> 50 

Phytoseiulus persimilis 

Specialist 

68-90 

60-90 

Table 1: Predatory mite species to be evaluated in HT cucumbers.

Predators will be evaluated in HTs on Corinto var. at SWPAC, PPAC and Meigs in year two, Meigs only in year three. TSSM will be inoculated to ensure even distributions. Three days post-inoculation each predatory species (Amblyseius andersoni, A. cucumeris, Neoseiulus californicus, N. fallacis) will be released simultaneously in each tunnel (one species per row). We will evaluate predatory mite persistence and changes in population of TSSM every three days for two weeks.

Phytoseiulus persimilis is a specialist species demonstrated to be effective at suppressing large TSSM populations, but they do not persist. We will evaluate their efficacy independent of other predators in a HT at Meigs. We will establish three levels of infestation of TSSM across rows, release the same number of P. persimilis across rows and measure reductions in TSSM populations seven days post-release. Leaves will be destructively sampled and rinsed in a hypochlorite solution to accurately count TSSM and predators following Wilson et al. (1983).

In all biocontrol trials a conventional miticide will be applied to eliminate mite populations between evaluations. We plan to re-inoculate and evaluate five times each year. This allows us to evaluate predator efficacy across the growing season, capturing changes in plant architecture and the environment.

3.2 Examine the efficacy of biopesticides to control TSSM in high tunnels.

There may be times when biological control is not feasible. As an alternative, we aim to provide evaluations on the efficacy of biopesticides in HT systems. Many of these products are oil or pathogen-based and can underperform or injure the plant when applied under high temperatures typical of HTs. Additionally, breakdown of the compound can be hindered by the filtration of UV-rays through the plastic covering or accelerated by the temperatures inside the HT. Therefore, it is crucial to perform efficacy trials in the environment under which they will be used. We will evaluate seven different products using two application methods, an electro-static sprayer and a backpack sprayer. The products are derived from the following active ingredients: neem; rosemary, geraniol and peppermint oil; cottonseed, clove and garlic oil; pyrethrin; potassium silicate; Chromobacterium subtsugae; Burkholderia spp. Efficacy trials will be conducted at PPAC and SWPAC in year one, at Meigs farm and on-farm with collaborators across all three years of the granting period. Ingwell, Yaninek and the graduate student will lead this effort.

Objective #4: Host field days, produce and disseminate new materials of IPM recommendations for TSSM control in HT cucumbers through Purdue Extension.

Field days will be hosted at PAC farms. Videos detailing sampling protocols, application of products or natural enemies and post-treatment evaluations will be produced and available on the Entomology Extension YouTube channel. Articles will be written throughout the project providing updates and published in Purdue Veg Crops Hotline. Results will be presented at conferences, including the Indiana Small Farm Conference and the Entomological Society of America.

We recognize the crucial role that the early adopters on our panel serve in the dissemination and adoption of new practices. We will include farmer experiences in our outputs, such as filming for the instructional videos incorporating their testimonies and presenting at meetings and field days. Participating farmers and researchers will host train-the-trainer events to disseminate findings to Extension educators throughout IN. Ingwell, Guan, Langenhoven, Maynard, Yaninek have Extension appointments and will contribute to this objective along with help from the graduate student.

References

Razmjou et al. (2011) Effect of vermicompost and cucumber cultivar on population growth attributes of the melon aphid (Hemiptera: Aphididae). J. Econ. Ent. 104(4): 1379-1383.

Edwards et al. (2010) Suppression of green peach aphid (Myzus persicae) (Sulz.), citrus mealybug (Planococcus citri) (Risso), and two-spotted spider mite (Tetranychus urticae) (Koch.) attacks on tomatoes and cucumbers by aqueous extracts from vermicomposts. Crop Prot. 29(1): 80-93.

Arancon et al. (2005) Suppression of insect pest populations and damage to plants by vermicomposts. Biores. Tech. 96(10): 1137-1142.

Wilson et al. (1983) Within-plant distribution of spider mites (Acari: Tetranychidae) on cotton: A developing implementable monitoring program. Environ. Ent. 12(1): 128-134.

Raworth (1986) Sampling statistics and a sampling scheme for the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) on strawberries. Can. Ent. 118(8): 807-814.

Hepworth and MacFarlane (1992) Systematic presence-absence sampling method applied to two-spotted spider mite (Acari: Tetranychidae) on strawberries in Victoria, Australia. J. Econ. Ent. 85(6): 2234-2239.

Iwao (1986) A new regression method for analyzing the aggregation pattern of animal populations. Res. Pop. Ecol. 10: 1-20.

Ruesink (1980) Introduction to sampling theory. Springer, New York, NY.

Ingwell et al. (2018) Tailoring insect biocontrol for high tunnels. Biol. Con. 123: 76-86.

 

Participation Summary

Education

Educational approach:

This project aims to engage and educate growers through a combination of presentations at Extension events, on-farm demonstrations provided at field days and the development of video training tools. A graduate student has been employed through this grant and is taking the lead on the research as well as aiding in the development of the educational tools. In August of 2020 a graduate student, Leslie Alejandro Aviles Lopez, was hired as the PhD student heading up this project in Dr. Ingwell's lab . We began our education approach with the aim to raise awareness of the pest and the project aimed at creating better strategies to manage this pest. Given the COVID situation, this has materialized in the form of virtual presentations at Extension events. In February 2021, Leslie presented a poster at the Indiana Small Farm Conference, which was held virtually. The poster, titled "Working to improve spider mite management in high tunnel cucumbers (Cucumis sativa L.), provided the opportunity to present the pest, cropping system, basic management information that we have available at the moment, objectives of the project and an opportunity for growers to become involved. In addition, at the in-person Small Farm Education Field day, held at the Purdue Student Farm in West Lafayette, IN on July 29, 2021 we hosted a station for participants to learn about the project and trained them to identify early signs and symptoms of spider mite infestation on cucumbers. There were 62 attendees at this field day. The Pinney Purdue Agriculture Farm, located in Wanatah, IN,  hosted a Vegetable Field Day on August 10, 2021. At this event the cucumbers that were part of our on-farm variety and efficacy trial were integrated into the event. Leslie and I taught participants how to identify spider mite damage, along with other insect pests and pathogens. We also had the opportunity to introduce the participants to the 10 varieties of cucumbers that we were evaluating in the research. The event attracted 23 attendees.

Project Activities

Pinney Purdue Vegetable Field Day
Small Farm Education Field Day
Indiana Small Farm Conference Poster Presentation

Educational & Outreach Activities

3 Curricula, factsheets or educational tools
1 Webinars / talks / presentations
2 Workshop field days
2 Other educational activities: Poster presentations at both the Entomological Society of America Annual Meeting and the International IPM Symposium. These events target researchers, Extension professionals, educators and students aspiring to work on IPM/Entomological topics.

Participation Summary:

459 Farmers
112 Ag professionals participated
Education/outreach description:

To date, we have had the opportunity to introduce the project and train individuals to identify two-spotted spider mites on cucumbers through one virtual poster presentation and two field days.

In 2022 we aim to increase farmer participation in the project. We have increased the advertisement of our survey to recruit on-farm collaborators and am directly contacting growers who have expressed support and interest in working on the project.

At professional society meetings, Leslie Aviles won second place for her poster presentation on the project at the Entomological Society of America Annual Meeting.

Learning Outcomes

Key areas taught:
  • Increased understanding of pest susceptibility among cucumber cultivars
  • Increased farmer ability to detect and monitor TSSM
  • Improved knowledge to implement biological control
  • Improved understanding of the efficacy of biopesticides in HTs

Project Outcomes

Key practices changed:
  • HT farmers select cucumber varieties more tolerant to TSSM

  • HT farmers scout for TSSM and train employees to identify early signs and symptoms

  • HT farmers implement biological control in a timely manner to suppress TSSM populations

  • HT farmers confidently select pesticides shown to manage TSSM in high tunnel cucumber production, and can apply them in a manner that achieves the desired level of control

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.