Dept. of Horticulture

Education and research for a green world

Welcome to the MagNet Website!

This site is devoted entirely to Delia radicum (L.) (Diptera: Anthomyiidae), which is also known by the common names of cabbage maggot, cabbage root fly, and turnip maggot.

Our program, a Vegetable Cropping Systems project, is a part of Oregon State University Extension Service and Dept. of Horticulture program. The program was initiated in fall 2000, with a mission of researching IPM strategies to manage the cabbage maggot and delivering information educational news to Brassica growers. For more information on the MagNet program, “jump” down to the Project Overview section on this page.

Don't forget to check out our Newsletters link to receive the latest news from our program. Also, use our Printable Version of Info Cards link to create a set of 3"x4" cards that you can laminate and carry in the field to aid in maggot identification and management.

This site is constantly under construction. Use the Key Players link to contact us with your questions, comments and suggestions. We hope you find this site useful, and we look forward to hearing from you!

Jump to: Goals and Objectives | 2005 Damage Update Project Overview–Introduction

Brassica vegetable crop growers in western Oregon are highly dependent on chlorpyrifos (Lorsban™; organophosphate), for control of their most important pest, the cabbage maggot (Diptera: Anthomyiidae; Delia radicum (L.)). Chlorpyrifos is a Food Quality Protection Act (FQPA)-targeted insecticide. Historically vegetable growers have not been interested in Lorsban alternatives due to high costs, lack of availability and lack of sound research and alternative products. However, the threat of its loss, environmental scrutiny, and potential development of resistence has increased grower willingness to test and adopt new management strategies. Chlorpyrifos has been shown to be neurotoxic to animals and aquatic organisms. The EPA has invoked the l0–fold safety factor for chlorpyrifos to compensate for the absence of reliable data that a chemical is safe, which has led to the elimination of many uses of this chemical. Chlorpyrifos is the second most frequently detected insecticide in surface waters of the Willamette Basin (Wentz, 1999). The Clean Water Act, the Endangered Species Act, OR Senate Bill 1010, the OR Plan for Salmon and Watersheds, and the Food Quality Protection Act have set in motion the development of a basin-wide water quality management plan and a statewide pesticide reporting use initiative. In addition, the fresh market production region (the Canby–Aurora area south of Portland) is urbanizing rapidly and farms are surrounded by homes, increasing the likelihood of human exposure to chlorpyrifos. (See Chlorpyrifos Risks)

As the maggot problem in Brassica crops was brought to our attention, a program was started called “MagNet”. The MagNet program involves a NETwork of people working together to develop a best management strategy targeting cabbage MAGgot management in western Oregon. Clearly, proactive implementation of a pest management strategic plan that reduces overall chlorpyrifos use, including monitoring, degree-day modeling, spatial management and rotation, field cultivation methods and sanitation, and alternative chemistry testing, is of strong interest to the growers.

During the first two years (2000-2001) of the program, we worked exclusively with root crops (e.g., daikon, turnip, radish, rutabaga). Root crops are an excellent system to study the maggot's life cycle and identify alternative management strategies for cabbage maggots, as the root is harvested and therefore damage is easy to assess. The system is highly sensitive, as even very low levels of infestation (a single maggot) can be detected. In addition, root crop growers plant small acreage plantings continuously throughout the growing season, so damage in space and time can be assessed. Cruciferous crops incur significant maggot damage so management strategies developed in root crops can then be applied to other cruciferous crops (e.g. broccoli, cabbage, cauliflower, kale, collards, and chinese cabbage - grown for both produce and seed).

In 2003–2005, we continued the development of a degree-day model in western Oregon to validate and predict spring emergence and seasonal flight. We also studied above-ground Brassicas plants (cauliflower and broccoli) to verify that the same IPM tools and principles emphasized can apply. Our findings may also be applicable to closely related fly species with very similar phenologies such as the seed corn maggot (Delia platura) and onion maggot (Delia antigua). The seed corn maggot damages corn, cotton, beans, beets, and potatoes and the onion maggot is the most serious insect pest of onion in temperate regions. Therefore, the impact of this project could be widespread in many vegetable production crops.

Goals and Objectives
Main Goal: To reduce the dependence on Chlorpyrifos use.

Objectives:

Quantify the current impact of cabbage maggot damage in western Oregon
Identify and validate and monitor techniques for IPM practices for mangement of maggots
Build a collaboration or network between growers, researchers, and agricultural professionals
Inspire grower IPM interest and adoption

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2005 Update

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Due to another mild winter with adequate precipitation in 2005, and little to no control by the use of Lorsban, the cabbage maggot (Delia radicum L.) pest proved to be a major and devastating problem in the Willamette Valley.

Cabbage maggot pressure was very high in the spring 2005!! We monitored for spring emergence, seasonal flight, and subsequent egg-laying on a weekly basis. Yellow water traps were placed around the Northern Valley to observe regional flight patterns. We caught more than 200 adult flies per week in our traps in early spring. That's more than we've captured in several years. We reported high egg levels of 30, 40, 60% on young plants followed by maggot tunneling on roots of only ¼ inch in size, levels that have proven to destroy fields. In early May, five chemically-treated root crop fields were disked under because of economically-high losses due to maggots. Field losses from cabbage maggots of 91.67, 88.22, 86.67, 83.33 and 78.33 percent were recorded.

Unfortunately, cabbage maggots were not controlled in the spring plantings, so pest pressure continued through the summer months. Typically, lower damage is seen from summer generations after an accumulation of 900-1000 degree-days (see degree-day model), depending on temperature and rainfall. However, the spring populations of maggots were so high, the summer plantings were in greater danger as reported.

Our data showed that cabbage maggot flies are more attracted to the young stems of the seedling plant at 5-9 leaf stage (long season crops, like rutabaga and turnips). One spray may not be enough for maggot control as a crop can be hit by 2 generations of flies. Also, there is a protracted spread of emergence hence a protracted period of egg-laying (5 weeks) in the spring. In addition, there's a reservoir of wild host weeds on the borders of fields and in neighboring nurseries that move into the Brassica crops.

The fall flight, another extremely high risk period, began in the northern Willamette Valley approximately September 1st and again in early October. We had increased field damage levels of 20-40% loss.

Growers need to take advantage of the knowledge that we have gained. There is no perfect treatment for maggot control. We do indeed need new chemistries for controlling the pest. Currently the only treatment we have is Lorsban (organophosphate; chlorpyrifos) and it is not working! We have applied to EPA for a Fipronil (Regent) registration, an efficacious treatment, but have not received it yet. Success (Spinosad) and Warrior (pyrethroid) can be used and have shown good control for the maggot and fly. In-furrow applications have higher efficacy rates and longer levels of protection than over-the-row broadcast applications. Most importantly, growers need to spatially move fields away from overwintering and seasonal maggot sources to help prevent future infestations. It is also important to harvest in a timely manner to prevent infestation from another generation.

Growers fields will not survive this pest pressure, Along with testing new chemistries for treating eggs and adults, we are also experimenting with row covers and exclusion fence use, field sanitation and clean-up of infested roots in field, spatial rotation away from maggot sources and highly-damaged plantings, wild weed host management, irrigation management for egg control, cultivation of harvested fields to reduce puparia, and more efficient application techniques for targeting eggs at base of plants. Return to top of page

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