Progress report for OS21-140
To combat heavy reliance on synthetic insecticides among conventional growers, and improve pest management options for organic growers, this project aims to evaluate the potential for biological control with beneficial entomopathogenic nematodes (EPNs) to help manage cucumber beetles and other pests of cucurbit crops. Biological control using EPNs can be part of an effective strategy for controlling many soil-dwelling insect pests, including cucumber beetles. However, despite promising results from previous studies, EPN biological control is still not widely used in U.S. agriculture and represents only a small fraction (about 0.03%) of the U.S. pest control market, indicating a critical need for continued research into EPN-based biocontrol strategies, as well as education and outreach to encourage greater use among U.S. producers. Research from our lab has revealed that applications of EPNs to plant roots can directly boost plant resistance to a variety of insect pests and pathogens, which suggests that growers can receive multiple benefits from EPN biological control, as EPNs both directly kill pest insects and boost plant resistance. We hypothesize that introducing EPNs will reduce insect damage and boost yield of cucurbit crops through two mechanisms, including both direct mortality of cucumber beetle larvae by EPNs and increased plant resistance against pests following plant exposure to EPNs. Furthermore, because EPNs will only be applied to soil near roots, we predict that they will not reduce numbers of beneficial insects visiting plants. We are evaluating EPN introductions for 3 different cucurbit crops, including cucumbers (Cucumis sativus), watermelons (Citrullus lanatus), and summer squash (Cucurbita pepo). This research will inform control potential in 3 important crops for our cooperator and the U.S. cucurbit market, and will particularly benefit growers on diversified farms seeking better management options.
We are evaluating the potential for entomopathogenic nematodes (EPNs) to provide biological control and boost plant resistance to improve pest management in cucurbit crops following two specific objectives:
- Determine the effectiveness of EPN biocontrol in cucurbit crops for reducing numbers of pest insects and plant damage, while preserving beneficial insect populations.
- Assess how introducing EPNs affects plant growth and yield.
- - Producer
Materials and Methods
This project is being conducted at Ronin Farm, which is a 15-acre diversified vegetable farm located in Bryan, TX. This project was developed in close collaboration with the owner, Mr. Brian Light, who expressed strong interest in improving pest management on his farm through sustainable strategies and incorporating biological control with beneficial nematodes as part of his management plan. Mr. Light selected the plant varieties for this project based on previous experience with produce quality and plant performance in Brazos county, TX. The entomopathogenic nematodes selected for this project are Heterorhabditis bacteriophora and Steinernema riobrave, which are suitable for southern climates and cucumber beetle control (Arbico Organics, USA).
This project will be conducted over two field seasons in 2021 and 2022, using randomized complete block design, similar to a previous EPN study (Ellers-Kirk et al., 2000). Each block will be divided into 2 rows and each row will receive one treatment: 1) plants treated with EPNs and 2) untreated control plants. Blocks will be replicated 4 times each for cucumbers, watermelons, and summer squash. Ronin Farm, and other growers in this area, typically plant the first cucurbit crops in March and make additional plantings through May. We will conduct our trials mid-season, starting in early April of each year. Plants will be grown and maintained following typical cultivation practices on Ronin Farm. Seeds will be planted directly into raised rows and thinned as needed. For cucumber, we will plant ~4 m long rows with 10 plants each, spaced 30 cm apart. For Summer squash, we will plant ~7 m long rows with 10 plants each, spaced 60 cm apart. For watermelons, we will plant ~9 m long rows with 5 plants each, spaced 1.5 m apart. Crops will be adjacent, and all rows will be 1 m apart. Cucumber vines will be trained onto trellises to promote airflow to leaves and facilitate easier surveys and harvest. Rows will be covered with straw mulch to suppress weeds and retain moisture and plants will be irrigated as needed.
EPN treatments will be applied twice per year to trigger plant resistance and target soil-dwelling pests like cucumber beetles. Plants will be treated with EPNs at 1 true leaf (~2 weeks after planting) and when they begin to flower and set fruit (~6 weeks). Each treatment plant will receive ~200,000 free-living EPNs in 100 mL water and control plants will each receive 100 mL water added to soil at the plant base.
Insect surveys and damage assessments
To quantify numbers of pest insects, we will conduct weekly visual surveys of all experiment plants from germination until final harvest (Skidmore et al., 2019). Each plant will be observed for 60 seconds to search for insects. If detected, insects will be sight identified (to species, family, or order as possible) and counted. Examples of insects in surveys include striped (Acalymma vittatum), spotted (Diabrotica undecimpunctata howardi), and banded (Diabrotica balteata) cucumber beetles, melon aphids (Aphis gossypii), squash bugs (Anasa tristis), squash vine borers (Melittia cucurbitae), leaf footed bugs (Leptoglossus zonatus), and silverleaf whiteflies (Bemisia tabaci). We will also assess cucumber beetle control using traps to monitor adult beetle emergence from soil. Traps (25 cm2, 12 cm tall) will be placed on the soil surface between plants in each row (4 per row for each plant species) 5 weeks after planting, allowing time for any adult beetles to lay eggs, and will be monitored twice weekly for 4 weeks (Ellers-Kirk et al., 2000).
During surveys, we will also quantify numbers of beneficial insects present on plants, allowing us to determine whether EPN introductions influence the beneficial insect community. Examples of insects to be surveyed (sight identification) include pollinators like honey bees (Apis mellifera), squash bees (Peponapis pruinosa), and other native bees (Osmia, Agapostemon, Bombus, Megachile sp., etc.), as well as natural enemies like wasps (e.g. Ichneumonidae, Braconidae, Vespidae, etc.), flies (Syrphidae), and beetles (e.g. Coccinellidae, Carabidae, etc.).
In separate weekly surveys, we will estimate % damage (insect or pathogen) area on leaves, flowers, and fruits.
Plant growth and yield data
To determine the effects of EPN introduction on plant biomass, we will quantify root length density following previously described methods (Ellers-Kirk et al., 2000). Briefly, soil cores will be taken near plant stems during the final week of harvest and cm root length per mm soil will be calculated. This will be replicated three times per row for all plant species. We will also record plant heights, numbers of leaves, and numbers of male and female flowers.
Yield data will be collected throughout the season as fruits are harvested. Fruits will be graded for marketability and total weight and fruit number recorded. The estimated harvest durations are: ~6 for weeks cucumber, ~6 weeks for squash, ~4 weeks for watermelon (Skidmore et al., 2019).
Data will be analyzed using the software program R. Data on insect numbers, damage estimates, plant growth, and yield will be analyzed using generalized liner mixed models. Additionally, to characterize the insect pest and beneficial communities present on each treatment, we will use multivariate community analyses, including Permutational Multivariate Analysis of Variance and non-metric multidimensional scaling ordination (Oksanen et al., 2019).
In the 2021 trials, we observed a slight (non-significant) reduction in cumulative pest damage for cucumbers and no effect in summer squash or watermelons for plots treated with EPNs. In the summer squash plots, we observed a severe infestation of squash vine borer (Melittia satyriniformis) that resulted in stunting and mortality across both treatments. Additional vine borer management tools will be implemented during the 2022 season. We also experienced a heavy, late-season infestation of leaffooted bugs (Leptoglossus zonatus) in all plots of cucumbers that resulted in some plant mortality. We are exploring additional management tools for this pest that can be incorporated in 2022. Similar numbers of cucumber beetle adults were observed EPN-treated and control plots for summer squash and cucumbers, but no beetles were detected in our emergence traps in any plots. Overall, similar numbers of pest and beneficial arthropod species were observed for EPN-treated and control plots for all three crops.
Plant growth traits (height or vine length and leaf number) were similar across treatments for all three crops. Notably, we observed higher yield in summer squash (~33% increase) and cucumber (~138% increase) and no difference in watermelon plots treated with EPNs compared to our control plots.
Educational & Outreach Activities
In 2021, our lab participated in the Ronin Spring Farm Day event, where we shared an exhibit on biological pest control and sustainable agriculture. Three graduate students and three undergraduate students from my research team participated in coordinating the exhibit and volunteering at the event. We met with over 200 members of the local community, including 2 local vegetable producers, who were very receptive to the research. We prepared and distributed 3 different educational materials/fact sheets on relevant topics, including 1) pests of cucurbit crops, 2) local pollinators, and 3) local natural enemies. We also led an on-farm demonstration of our research.
In 2021-2022, PI Helms also presented results from this project in 4 research seminars. She also met with members of the vegetable IPM team from Cornell University to discuss strategies for implementing EPNs for controlling cucurbit pests in upcoming trials.