The long-term goal of this project is to identify abiotic factors associated with increased onion maggot pressure and control failures and to evaluate how those factors may impact control measures, specifically seed treatments. To achieve this goal, I propose the following objectives:
1) Evaluate associations between local climate and soil conditions (temperature and moisture) on the occurrence and relative pressure of onion maggot across onion producing regions of New York. We hypothesize that regions with greater seasonal precipitation, higher soil moisture, and lower temperature maxima will have a greater relative abundance of onion maggot compared with fields that have lower precipitation and soil moisture and higher temperature maxima in the spring.
2) Assess uptake and dissipation of novel, reduced-risk seed treatments used in the control of onion maggot.
The purpose of this project is to evaluate how climate and soil conditions, specifically soil moisture, impact the abundance of onion maggot, Delia antiqua (Diptera: Anthomyiidae) and to assess the performance of insecticide seed treatments used for its control. The goal of this research is to improve prediction and management of this pest and to reduce grower reliance on chlorpyrifos, an organophosphate insecticide applied as a drench treatment at planting in an attempt to improve onion maggot control provided by insecticide seed treatments.
New York accounts for over 90% of production in the Northeast and ranks 6th in national onion production. With an annual value of 40-50 million dollars, onion is one of the most important vegetable crops grown in the state (NASS 2017). Closely related to other root feeding maggot species, including seedcorn maggot (Delia platura) and cabbage maggot (Delia radicum), onion maggot feeds on the below-ground portion of onions (roots and bulb). As adults, flies lay their eggs on or at the base of onion plants and once hatched, the larvae move into the root zone, enter the basal plate, and begin feeding. Onion seedlings are most susceptible to damage by onion maggot, which can result in crop losses greater than 50% (Taylor et al. 2001; Nault et al. 2006a). For this reason, protecting the crop against this pest is essential.
Growers manage onion maggot using a combination of cultural controls (e.g. crop sanitation) and insecticides applied at planting, primarily as seed treatments. Currently, the most widely adopted seed treatment package is Syngenta’s FarMore®FI500, which includes two active ingredients against onion maggot, thiamethoxam (neonicotinoid) and spinosad (spinosyn). Thiamethoxam alone is not effective against onion maggot, suggesting that spinosad is the most important of the two (Nault et al. 2006b). Spinosad, a reduced-risk insecticide, is labeled as a foliar spray on many fruit and vegetable crops but is labeled as a seed treatment exclusively on onion. For many growers, FarMore®FI500 is highly effective, and growers achieve >90% control of onion maggot. However, a subset of NY growers consistently experiences onion maggot control failures. This is surprising given that those with damage and those without plant onions in the same soil type (muck soils), employ similar management strategies, cultivate the same varieties, plant at the same seed density, and seldom rotate out of onions. Consequently, growers facing control failures often resort to augmenting seed treatments with in-furrow drenches of chlorpyrifos (Lorsban®), sometimes at rates far greater than those recommended. Field trials have shown that chlorpyrifos is not very effective against onion maggot (Nault et al. 2006c). Moreover, due to concerns regarding negative non-target environmental and health effects, resistance, and future availability, chlorpyrifos likely will be phased out of use. Therefore, research is needed to understand what factors are associated with high onion maggot pressure and failure of seed treatments to protect against the pest.
The information generated from this study can be used to inform more sustainable management recommendations for the control of this pest moving forward. For instance, understanding what factors put growers at risk for damage by onion maggot can inform prophylactic measures, such as crop rotation, and elucidating the uptake and dissipation dynamics of seed treatments can reveal the temporal window of protection offered by this control. These findings will lay the groundwork for better predictive abilities and more precise control measures against this devastating pest.
Objective 1: To assess the effect of abiotic factors (temperature and moisture) on adult abundance and larval damage by onion maggot.
Temperature and precipitation monitoring 2018
Beginning 14 May 2018 and ending 11 July 2018, soil and air temperature and weekly precipitation was monitored in 15 fields in central NY located across 6 counties: Oswego, Wayne, Steuben, Yates, Orleans, and Genesee. Fields can be grouped into three main regions, Oswego/Wayne in the east, which have historically reported severe damage by onion maggot, Orleans/Genesee in the west, which do not report significant losses from the pest, and Yates/Steuben, located within the Finger Lakes region and has historically reported variable damage. Soil and air temperature were monitored using iButton temperature probes (Model DS1922G#F50, Thermochron Temperature Solutions, New South Wales, Australia), which recorded temperature every 15min. Probes were placed in 50ml polypropylene conical centrifuge tubes (FalconTM, Thermo Fisher Scientific) filled with dry Turface MVP® (Profile Products LLC, Buffalo Grove, IL). Soil temperature was monitored by burying two probes, positioned 30m apart, in the top 5cm of soil in each field, and air temperature was monitored by one probe attached to a pole approximately 1m above the ground. Precipitation was monitored on a weekly basis using rain gauges positioned approximately 1.5 m above the ground.
In addition to temperature and precipitation, each week, onion plant growth parameters, including plant height, neck diameter, and leaf stage, were measured on 10 randomly selected plants. Along with planting date, these data will serve to distinguish plant phenology and development at each field site throughout the sampling period.
Fly monitoring and larval damage assessments 2018
In order to approximate adult fly abundance, three sticky cards, positioned 30 m apart, were mounted on stakes at plant height along one edge of each field site. Sticky cards were collected and replaced on a weekly basis. Beginning 4 June, fields were assessed for onion maggot damage; prior to this date, no damage was observed. Onion maggot damage was assessed each week by walking two 50 m transects within each field and identifying plants with symptoms of maggot damage (wilted leaves, entry wounds, and active feeding).
Soil characteristics 2018
Soil from each field was collected the week of 9 July. Soils were sampled from nine places in a 100m x 100m array at each field site. At each point in the array, a composite sample of five soil plugs, 6-10cm in depth and 5.5cm in diameter were collected. Samples were dried and stored, and will be analyzed for pH, moisture holding capacity, organic matter content, and texture in January and March 2019.
Management Survey 2018
In order to compare management practices at each field site, each participating grower was asked to provide information on planting date, onion variety, planting density, seed treatment, application of chlorpyrifos, and year since last crop rotation out of onion.
Objective 2: Assess uptake and dissipation of novel, reduced-risk seed treatments used in the control of onion maggot.
Spinosad uptake assay 2018/2019
In order to determine if and to what extent spinosad, the primary component of FarMore® FI500, is taken up by onion plants during plant growth, a greenhouse uptake study is taking place. Pelleted onion seeds with and without spinosad will be grown under greenhouse conditions in muck soil. At four and eight weeks, plants will be harvested, and spinosad content in aboveground tissue, belowground tissue, rhizosphere soil, and bulk soil will be measured using HPLC. In addition to analyzing uptake of spinosad in onions through time, larvacidal effects of these onions will also be assessed with a bioassay. First instar larvae will be exposed to onion plants grown from 4 and 8 week old spinosad treated or untreated seeds in no-choice and choice tests. Mortality will be evaluated after 24 and 48 hours.
In the spring of 2018, from mid May to Mid July, soil and air temperature, weekly precipitation, and weekly fly abundance and larval damage was monitored in 15 fields across central NY. Sticky cards are currently being assessed for adult fly abundance using visual identification as well as DNA barcoding. Data have not yet been analyzed for statistical significance, but relationships between precipitation, temperature, fly abundance, and larval damage will be evaluated. Preliminary results suggest that precipitation from mid-May to mid-July had no effect on larval damage observed in fields. However, in 2018, all growers reported using FarMore®FI500 seed treatments in their fields but chlorpyrifos was applied at various rates to fields, ranging from 0 to 5 qt/acre. For this reason, the damage observed in each field may not accurately reflect the efficacy of the seed treatment or the effects of precipitation, and consequently, the effects of abiotic factors on fly abundance rather than larval damage will be compared at each site. Another year of this data will be collected beginning in May 2019.
Plants are currently being grown in the greenhouse for the spinosad update assays and larval choice and no-choice bioassays. These data will be collected in January/March 2019.
Education & Outreach Activities and Participation Summary
On 22 August 2018, I presented at the Oswego Onion Growers Twilight Meeting, which took place in Oswego County and hosted approximately 60 growers from Oswego and other adjacent counties, industry representatives, and extension personnel. This meeting occurs annually and serves as a way to discuss the growing season and major findings from research conducted during the summer. Using a summary handout, I briefly explained the goal of the project and some of our preliminary findings regarding precipitation and larval damage and fielded questions from growers regarding the project. In March 2019, I will present the 2018 data at the Entomological Society of America Eastern Branch Meeting in Blacksburg, VA in the student talk section. This spring, I also plan to co-author an extension article for VegEdge, a Cornell Cooperative Extension newsletter from the Cornell Vegetable Program, which will outline recommendations for growers to rotate seed treatments on an annual basis.
In the summer and fall of 2018, the project outcomes were mainly in the form of grower contact. Working on this project, we met with growers sometimes on a weekly basis while monitoring their fields. These served as valuable opportunities to discuss the project with growers and to hear their concerns and management approaches. We were able to use these discussions to remind growers of the importance of rotating their fields and using different seed treatments.
Because this project is newly underway, we are still in the process of synthesizing our findings, adjusting our research approach, and understanding the implications for sustainable agriculture. Nevertheless, the damage reported this summer by some growers, about 30% by one grower, has highlighted the need to look for more sustainable and less chemically reliant approaches to managing onion maggot across the region. There is some interest in pursuing the sterile male technique used in Quebec for control of the pest and introducing entomopathogenic nematodes in the region. Our research, which seeks to determine conditions that favor onion maggot, can contribute to these long-term goals by identifying high risk regions that can be targeted with new approaches. Similarly, understanding the dissipation and uptake dynamics of spinosad can provide basic knowledge needed to understand how this approach works to control the pest and insight into how long this protection is effective during the growing season. In the spring of 2018, we applied for and received a $1000 grant to aid in the costs of HPLC analysis for the uptake studies.