Progress report for GNE24-306
Project Information
Maggots (Delia spp.) are devastating below-ground pests of onions and cabbage in the Northeast. These crops are among the most valuable vegetable crops in this region, and damage can cause yield losses of up to 50%. Over one-third of the onion acreage and nearly all of the cabbage acreage are transplanted, and growers typically relied on at-planting applications of chlorpyrifos to control maggots. The EPA banned chlorpyrifos in 2022, and now there is a demand to identify effective insecticides that will protect transplanted onion and cabbage fields from maggots. Research is needed to identify reduced-risk insecticides that are effective against maggots as well as safe for pesticide applicators and the environment. Additionally, further research is needed to examine the impact of entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN) as insecticides for controlling maggots in transplanted crops. Anticipated benefits from this project include improving crop production by decreasing pest damage with safer pest management solutions for applicators and the environment and mitigating resistance development by identifying a series of insecticides that could be used in rotation strategies.
The goal of this project is to identify reduced-risk insecticides to protect onion and cabbage transplants from maggot pests that are also safe for pesticide applicators and sustainable for these cropping systems. To achieve this goal, I propose the following objectives:
- Identify reduced-risk insecticides applied as tray drenches to control onion maggots (D. antiqua) in onions. We hypothesize that all insecticides will provide an acceptable level of onion maggot protection.
- Identify reduced-risk insecticides applied as tray drenches to control cabbage maggot (D. radicum) in cabbage. We hypothesize that all insecticides will provide an acceptable level of cabbage maggot protection.
The purpose of this project is to evaluate the performance of reduced-risk insecticides for the control of maggot pests in onions and cabbage. Insecticides considered “reduced-risk” have a low impact on human health, lower toxicity to non-target organisms, and a low potential for groundwater contamination. The onion maggot (Delia antiqua) and cabbage maggot (Delia radicum) are among the most important early-season pests of transplanted onions and cabbage in the Northeast, respectively. Seedcorn maggot (Delia platura) also attacks both crops and has always been considered a secondary pest relative to D. antiqua and D. radicum (Salgado & Nault unpublished data, Savage et al., 2016). To protect these crops from all maggot species, chloryprifos was used at planting in transplanted onion and cabbage fields. However, the EPA banned chlorpyrifos from all food crops, including onions and cabbage, leaving growers with no known effective alternatives. Research is needed to identify insecticides that are effective for protecting onion and cabbage from maggots, especially products that are considered reduced-risk that are safer to the applicator and environment.
Onions and cabbage are two of the most important vegetable crops in the Northeast. Onion production in New York constitutes 97% of the production in the northeastern United States and ranks eighth in the country. Cabbage production in New York ranks in the top three nationally, with 5,000+ acres harvested per year (USDA NASS, 2023). Sales of both crops exceed USD 100 million annually (USDA NASS, 2023).
In the northeastern US, onions are primarily grown in soils drained from swamps called “mucks,” which are soils with high organic matter and nutrient content (Stephens, 1955). Onions are transplanted between April and early June in the Northeast. The two most common types of onion transplants are either bare root (imported from Arizona) or plugs (grown locally or imported from Canada). Cabbage is grown on mineral soils and is transplanted between late April and July. The two most common types of cabbage transplants are also either bare root (imported from Georgia and Florida) or plugs (grown locally). Because onions and cabbage are transplanted in the spring when soil conditions are typically cool and wet, maggots (Delia spp. [Diptera: Anthomyiidae]) are a serious pest problem for these growers. In the onion crop, onion maggot (D. antiqua) and seedcorn maggot (D. platura) occur throughout northern onion production regions in the US, but differ in abundance and pest status in each region. Preliminary results (Salgado & Nault unpublished data) showed that the onion maggot is more abundant than the seedcorn maggot in New York onion fields. In cabbage, the cabbage maggot (D. radicum) was reported to be the most abundant Delia species (Savage et al., 2016). For all maggot species, flies lay their eggs on or at the base of onion or cabbage plants, and larvae move into the root zone and begin feeding. Damage occurs mainly on the below-ground portion of plants, reducing yields by decreasing stand counts in heavy infestations (Nault et al., 2006; Salgado et al., 2023).
Onion growers have no effective insecticide options for protecting onion transplants from maggots. Cabbage growers can use directed foliar applications of pyrethroid insecticides (e.g., Mustang Maxx and Hero) when flies are active, but this approach has generated inconsistent results. Recently, preliminary field trials have shown that at-plant applications of cyantraniliprole (Verimark) and chlorantraniliprole (Coragen) can protect transplanted cabbage from D. radicum (Salgado et al., 2023). However, very little is known about the efficacy of reduced-risk insecticides and biological products for protecting onion and cabbage transplants from maggots.
Research is needed to identify insecticides that are effective against these maggot pests but are safe for pesticide applicators and sustainable for these cropping systems. This project will contribute to Northeast SARE’s outcome statement by finding actionable solutions by doing on-farm research that can help growers mitigate pest damage and maintain crop yields, gain more knowledge to reduce reliance on insecticides that are harmful to applicators and the environment, and indirectly support these agricultural businesses’ sustainability and profitability.
Cooperators
- (Educator and Researcher)
- (Educator and Researcher)
Research
Objective 1: Identify reduced-risk insecticides applied as tray drenches to control onion maggot (D. antiqua) in onions.
Treatments. The experiment included the following treatments: 1) No insecticide, 2) commercial formulation of spinosad, 3) commercial formulation of cyantraniliprole, 4) commercial formulation of Beauveria bassiana, 5) commercial formulation of Metarhizium sp., 6) commercial formulation of Steinernema feltiae and Heterorhabditis bacteriophora, and 7) commercial formulation of Bacillus thuringiensis, subsp. Israelensis (Table 1.) Table 1. List of treatments with rates for reduced-risk insecticides for onion.
|
Trt# |
Products |
Active ingredient(s) |
Rate of formulated product(s) |
Rate per plant |
Rate per tray |
|
1 |
Untreated control |
- |
- |
- |
- |
|
2 |
Entrust SC |
spinosad |
8 fl oz/acre |
0.0013 ml |
0.75 ml |
|
3 |
Verimark |
cyantraniliprole |
13.5 fl oz/acre |
0.0022 ml |
1.24 ml |
|
4 |
BoteGHA ES |
Beauveria bassiana Strain GHA, 11.3% |
64 fl oz/acre |
0.0103 ml |
5.93 ml |
|
5 |
LALGUARD M52 OD |
Metarhizium brunneum strain F52 |
80 fl oz/acre |
0.0128 ml |
7.37 ml |
|
6 |
NemAttack™ & NemaSeek™ Combo Pack Sf/Hb |
Steinernema feltiae & Heterorhabditis bacteriophora |
250,000,000 infective juveniles per acre |
1,356 infective juveniles |
781,056 infective juveniles |
|
7 |
Gnatrol WDG |
26 oz per 100 gallons of water |
Bacillus thuringiensis, subsp. israelensis, strain AM 65-52 |
3.38 mg |
1,947 mg |
Site selection and experimental design. Field trials were conducted on two commercial farms in Oswego, NY (Farm G and J). These sites were specifically selected based on grower reports of historically high maggot pressure, ensuring a robust challenge for insecticide treatments. While a Wayne County site was originally planned, we were unable to conduct a trial there because of weather conditions. Transplant plugs were transplanted on 21 May at both sites. Each plot had two rows (10 ft long) that were separated by 10 inches; plots were separated from each other within rows by a 5-ft alley of bare soil at both sites. There were no guard rows. Transplant plugs (var ‘Oneida’) were hand transplanted at a density of 2.5 plants per foot (50 plugs per plot). There were a total of six (Farm G) and seven treatments (Farm J) at each location, respectively (Table 2), including the no-insecticide control, that were arranged in a randomized complete block design and replicated 5 times.
One week after transplanting, and when onion maggot flies were active, the number of plants wilting and dying from onion maggot feeding was recorded. Each damaged onion plant was pulled to make sure that it was infested with onion maggot or recently had been infested with maggots. These data were taken at least once per week in both rows of each plot. At both locations, data were collected on 3, 12, 17, 24 June, and 1 and 8 July. The final damage assessment was made at the end of the first generation in early July, and a final plant stand count was also made. Phytotoxicity was observed in treatment #5 (LALGUARD M52 OD).
Because onion stand loss from abiotic factors (e.g., wind, drought, and heat) and biotic ones like seedling diseases (e.g., damping off, onion smut) could confound the assessment of the number of plants killed by maggot feeding, data were analyzed in the following manner. First, the cumulative number of seedlings killed by first-generation onion maggots was determined (= sum of all plants killed by maggots through 3 or 8 July). Next, this total was divided by the sum of all maggot-killed plants plus the final number of healthy plants recorded on 8 July. This quotient was the final percentage of plants killed by onion maggot.
Data were analyzed separately by location using a generalized linear mixed model using the adaptive quadrature method (PROC GLIMMIX, SAS® Institute 2013). The proportion of damaged plants was best fit using a beta distribution with a logit function. The model included insecticide tray drench as a fixed effect and replication as a random effect. Tukey’s Honest Significant Difference [HSD] (α=0.05) test was used for mean separations. Predicted values of least square means and standard errors converted from the logit or log scale to the data scale (ilink option) are presented.
Trials for 2026 will be transplanted in April/May and maintained by Salgado and temporary staff.
Performance Measure for Onion Trial 2026. We expect to identify insecticide(s) applied as a tray drench treatment that will effectively protect the onion crop from maggot damage. Treatments with ≤5% maggot damage plants will be considered commercially acceptable)
Objective 2: Identify reduced-risk insecticides applied as tray drenches to control cabbage maggot (D. radicum) in cabbage.
Treatments. The experiment included the same treatments as objective 1 (except Gnatrol), in addition to two insecticides suggested by the grower and extension agent collaborators, but at different rates adjusted to plant density (Table 3).
Table 3. List of treatments with rates for reduced-risk insecticides for cabbage.
|
Trt# |
Products |
Active ingredient(s) |
Rate of formulated product(s) |
Rate per plant |
Rate per tray |
|
1 |
Untreated control |
- |
- |
- |
- |
|
2 |
Entrust SC |
spinosad |
10 fl oz/acre |
0.0170 ml |
4.90 ml |
|
3 |
Verimark |
cyantraniliprole |
13.5 fl oz/acre |
0.0229 ml |
6.60 ml |
|
4 |
BoteGHA ES |
Beauveria bassiana Strain GHA, 11.3% |
64 fl oz/acre |
0.1086 ml |
31.28 ml |
|
5 |
LALGUARD M52 OD |
Metarhizium brunneum strain F52 |
80 fl oz/acre |
0.13578 ml |
39.11 ml |
|
6 |
NemAttack™ & NemaSeek™ Combo Pack Sf/Hb |
Steinernema feltiae & Heterorhabditis bacteriophora |
250,000,000 infective juveniles per acre |
14,349 infective juveniles |
4,132,512 infective juveniles |
|
7 |
Coragen |
chlorantraniliprole |
5 fl oz/acre |
0.0083 ml |
2.4 ml |
|
8 |
Capture LFR |
bifenthrin |
6.8 fl oz/ acre |
0.0118 ml |
3.4 ml |
Site selection and experimental design. This study was conducted in 2025 on one commercial cabbage farm in mineral soil near Oakfield, New York. Greenhouse-grown plug transplants of green cabbage (Variety Bourbon) were hand-transplanted on 28 April. Plots were 2 rows wide by 15 ft long. Row spacing was 32 inches, and plots were separated from each other within rows by 40 inches (101.6 cm). Plant spacing was 10 inches for a planting density of 17,424 plants/acre (43,056 plants/ ha). Eight treatments, including the non-treated control, were arranged in an RBCD and replicated 5 times. Tray drenches were applied evenly across all seedlings in 288-cell tray using a volume of 1 liter of solution/tray (33.81 fl oz/ tray). These applications were made using a CO2-pressurized backpack sprayer and a single Teejet flat fan VS 8004 nozzle at 30 PSI. Treatments were applied 24 hours before transplanting. Originally, we also had another farm in Ontario County, NY that was going to participate in this project, but due to weather conditions, the site had to be excluded.
Twenty plants per plot (excluding stunted plants) were sampled 38 days after transplant (5 June) to record the cabbage maggot damage per treatment. Plants were uprooted with a trowel and inspected for the presence of cabbage maggot larvae and pupae. Plant roots were rinsed in water to remove excess soil and inspected for cabbage maggot feeding damage, which was characterized by discoloration and galleries in the roots and lower stem. Phytotoxicity was observed in treatment #5 (LALGUARD M52 OD). The response variable was defined as the percentage of damaged plants, which consisted of the sum of all plants with the presence of cabbage maggot larvae and pupae, and/or signs of larval damage.
Data were analyzed using a generalized linear mixed model using the adaptive quadrature method (PROC GLIMMIX, SAS® Institute 2013). The proportion of damaged plants was best fit using a beta distribution with a logit function. The model included insecticide tray drench as a fixed effect and replication as a random effect. Fisher’s Least Significant Difference [LSD] (α=0.05) test was used for mean separations. Predicted values of least square means and standard errors converted from the logit or log scale to the data scale (ilink option) are presented.
Trials for 2026 will be transplanted in April/May and maintained by Salgado and temporary staff.
Performance Measure for Cabbage Trial 2026. We expect to identify insecticide(s) applied as a tray drench treatment that will effectively protect the cabbage crop from maggot damage. Treatments with ≤5% maggot damage plants will be considered commercially acceptable.
Reporting Period: August 2024 to January 2025
During this reporting period, we engaged with a representative from Certis Biologicals to discuss their range of biological products. Following these discussions, Certis agreed to provide us with select products for our trials. Instead of using BotaniGard Maxx, we opted to test BoteGHA ES to focus on the specific effects of Beauveria bassiana. Unlike BotaniGard Maxx, which combines Beauveria bassiana with a pyrethroid, BoteGHA ES contains only Beauveria bassiana.
Additionally, we conducted preliminary meetings with our collaborators to finalize the treatment list for the upcoming field season and to strategize preparation efforts for our trials. In February and March, we plan to begin contacting grower collaborators to discuss space allocations and plant requirements for the field trials.
Reporting Period: January 2025 to January 2026
Objective 1: Identify reduced-risk insecticides applied as tray drenches to control onion maggot (D. antiqua) in onions.
Early in the season, precipitation was higher, and temperatures were cooler than average, leading to maggot outbreaks across parts of New York State. Later, rainfall and temperatures returned to more typical levels. Soil conditions at Farm G were saturated at planting, making conditions favorable for maggot activity, while conditions were ideal at Farm J.
Maggot pressure was high at the Farm G location (79.4% of the plants were infested by maggots in the no-insecticide control). In comparison, maggot pressure was moderate at the Farm J location (29.0% of the plants in the no-insecticide control were infested by maggots). In both locations, only Entrust SC, Verimark, BoteGHA ES, and Gnatrol WDG insecticide tray drenches reduced the percentage of plants killed by maggots compared with the no-insecticide controls.
At the Farm G site, there were significant differences in efficacy among the treatments (F = 24.8; df 5, 20; P < 0.001), Entrust SC was the most effective treatment, resulting in the lowest percentage of damaged plants and significantly outperforming all other treatments (Table 4). Verimark and BoteGHA ES provided an intermediate level of control. While they had a higher percentage of damaged plants compared to Entrust SC, they were statistically similar to each other and significantly better than the untreated control (Table 4). LALGUARD M52 OD and the combination of NemAttack & NemaSeek failed to reduce damage. Both treatments resulted in infestation levels that were statistically comparable to the no-insecticide control.
At the Farm J site, treatment separation was less distinct due to lower overall pressure, but significant differences remained (F = 5.8; df = 6, 24; P = 0.0008). Verimark, Entrust SC, and BoteGHA were the most effective treatments. Verimark had the lowest numerical damage, though it was statistically similar to Entrust SC and BoteGHA ES. Gnatrol WDG showed moderate efficacy, performing numerically better than the control but not statistically comparable to Verimark. At this location, practical resistance to spinosad (Entrust SC active ingredient) as a seed treatment was first detected in 2023.
Table 4. Mean percentage of onion plants, ‘Oneida’, killed by onion maggot, Delia antiqua, and seedcorn maggot, Delia platura, in various insecticide tray drenches on two commercial farms near Oswego, NY, in 2025.
|
Trt # |
Product(s) |
Rate of formulated product(s) |
Active ingredient(s) |
Mean percentage of damaged plants per plota (LS Means ± SEM) |
|
|
Farm G |
Farm Jb |
||||
|
1 |
Untreated control |
- |
- |
79.4 ± 5.0a |
26.2 ± 4.8ab |
|
2 |
Entrust SC |
8 fl oz/acre |
spinosad |
25.6 ± 5.4c |
8.9 ± 2.8cd |
|
3 |
Verimark |
13.5 fl oz/acre |
cyantraniliprole |
47.0 ± 6.7b |
6.6 ± 2.3d |
|
4 |
BoteGHA ES |
64 fl oz/acre |
Beauveria bassiana strain GHA, 11.3% |
59.9 ± 6.4b |
11.7 ± 3.3cd |
|
5 |
LALGUARD M52 OD |
80 fl oz/acre |
Metarhizium brunneum strain F52 |
84.1 ± 4.1a |
32.7 ± 5.2a |
|
6 |
NemAttack™ & NemaSeek™ Combo Pack Sf/Hb |
250,000,000 infective juveniles per acre |
Steinernema feltiae & Heterorhabditis bacteriophora |
87.8 ± 3.6a |
27.0 ± 4.9ab |
|
7 |
Gnatrol WDG |
26 oz per 100 gallons of water |
Bacillus thuringiensis, subsp. israelensis, strain AM 65-52 |
N/A |
18.6 ± 4.2bc |
a Means followed by the same letter are not significantly different (P > 0.05; Tukey’s Honest Significant Difference [HSD] (α=0.05); n = 5).
b Practical resistance to the active ingredient spinosad delivered as a seed treatment was first detected in 2023.
Objective 2: Identify reduced-risk insecticides applied as tray drenches to control cabbage maggot (D. radicum) in cabbage.
Conditions were favorable for planting, with precipitation above average in the weeks leading up to planting. However, soil conditions on the farm were dry from mid-May to the first week of June.
Cabbage maggot pressure was moderate in this trial, as only 19% of the plants in the untreated control were damaged by maggots (Table 5). There were significant differences in efficacy among the treatments (F = 4.1; df 7, 28; P = 0.0031). Coragen, Verimark, and Entrust SC were the only tray drenches that significantly reduced the percentage of damaged plants compared to the untreated control.
Verimark and Entrust SC provided the greatest numerical protection, resulting in the lowest percentage of damaged plants. These two treatments significantly outperformed all others in the trial, except Coragen. In contrast, Capture LFR, the NemAttack™ & NemaSeek™ combination, BoteGHA ES, and LALGUARD M52 OD did not differ significantly from the untreated control.
Table 5. Mean percentage of cabbage plants, ‘Var. Bourbon’, killed by cabbage maggot, Delia radicum, in various insecticide tray drenches on one commercial farm near Oakfield, NY, in 2025.
|
Trt# |
Products |
Rate of formulated product(s) |
Active ingredient(s) |
Mean percentage of damaged plants (LS means ± SEM) |
|
1 |
Untreated control |
- |
- |
19.4 ± 5.1a |
|
2 |
Entrust SC |
10 fl oz/acre |
spinosad |
2.6 ± 1.3c |
|
3 |
Verimark |
13.5 fl oz/acre |
cyantraniliprole |
2.7 ± 1.3c |
|
5 |
BoteGHA ES |
64 fl oz/acre |
Beauveria bassiana Strain GHA, 0.06% |
12.7 ± 4.1ab |
|
5 |
LALGUARD M52 OD |
80 fl oz/acre |
Metarhizium brunneum strain F52 |
9.7 ± 3.5ab |
|
6 |
NemAttack™ & NemaSeek™ Combo Pack Sf/Hb |
250,000,000 infective juveniles per species per acre |
Steinernema feltiae & Heterorhabditis bacteriophora |
13.1 ± 4.4ab |
|
7 |
Coragen |
5 fl oz/acre |
chlorantraniliprole |
5.8 ± 2.4bc |
|
8 |
Capture LFR |
6.8 fl oz/ acre |
bifenthrin |
16.0 ± 4.7a |
aMeans followed by the same letter are not significantly different (P > 0.05; Fisher’s Least Significant Difference [HSD] (α=0.05); n = 5).
Reporting Period: January 2025 to January 2026
Objective 1: Identify reduced-risk insecticides applied as tray drenches to control onion maggot (D. antiqua) in onions.
Results from Year 1 suggest that Entrust SC, Verimark, and BoteGHA ES were the most effective tray drench treatments for controlling onion maggots, consistently reducing plant damage across both high- and low-pest-pressure environments. While Entrust SC offered superior protection under severe infestation conditions at Farm G, Verimark and BoteGHA ES provided control, statistically comparable to the top performer, particularly at lower pressure settings. Additionally, phytotoxicity was observed in LALGUARD M52 OD, suggesting a lower rate or another formulation needs to be tested in 2026.
Objective 2: Identify reduced-risk insecticides applied as tray drenches to control cabbage maggot (D. radicum) in cabbage.
Results from Year 1 demonstrates significant variation in the efficacy of insecticide tray drenches against cabbage maggot in transplanted cabbage. While pest pressure was low, Verimark and Entrust SC demonstrated higher efficacy, significantly outperforming the untreated control and most other treatments. Coragen also resulted in significantly lower damage rates compared to the control. In contrast, the pyrethroid Capture LFR and the biological treatments (NemAttack™ & NemaSeek™, BoteGHA ES, and LALGUARD M52 OD) did not provide significant crop protection under these trial conditions. Additionally, phytotoxicity was observed in LALGUARD M52 OD, suggesting a lower rate or another formulation needs to be tested in 2026.
All trials will be repeated in 2026, with the addition of Neemix 4.5 (Azadirachtin) to expand the potential toolkit for organic and conventional growers.
Education & outreach activities and participation summary
Participation summary:
The results and outputs from this project will benefit the target stakeholder group (onion and cabbage growers) by helping them select reduced-risk insecticides to control maggots in onions and cabbage. To reach our immediate stakeholders, I presented at the 2025 Muck Onion Growers Twilight Meeting in Oswego (see attached handout and picture), where 75 people from Oswego and other adjacent counties, industry representatives, and extension personnel participated. Additionally, our collaborator from Orange County, NY (Ethan Grundberg) shared our results with the growers in that region.
Fact sheets are being developed as we finalize the experiments to support our conclusions.
Project Outcomes
- Based on some of these results and other trials we have conducted over the years, NYDEC granted a Section 2(ee) for the use of Verimark as a tray drench in onions for maggot control.
- By validating the efficacy of diamides (Verimark) and biologicals (BoteGHA ES), we are enabling growers to adopt chemistries that have lower toxicity to non-target organisms and are safer for pesticide applicators compared to historical standards like chlorpyrifos.
- Our identification of phytotoxicity in LALGUARD M52 OD at tested rates prevents growers from incurring financial losses due to crop injury, highlighting the importance of our safety screenings before wide-scale farmer adoption.
- During the Jan 2025–Jan 2026 period, the graduate student (project manager) was awarded the Paul J. Chapman Fellowship (May 2025–May 2026). This fellowship covered a full stipend, tuition, and fees. Consequently, NESARE funds originally allocated to half of the summer 2025 salary were not utilized and will be used to cover the full 2026 summer salary.