2005 Interim Best Management Practices to Control the Swede Midge (Contarinia nasturtii Kieffer)

Table of Contents

1. Introduction
   • Background of swede midge in Ontario
   • Quarantine pest
2. Challenges
   • Identification
   • Life Cycle
3. Best Management Practices
   • Greenhouse Sanitation
   • Crop Rotation
   • Field Selection
   • Crop Selection
   • Field Sanitation
   • Planting and Harvesting Dates
   • Monitoring / Scouting
   • Insecticide Spray Timing
4. Final Thoughts and Take Home Messages
5. Related Links

Introduction

Background of swede midge in Ontario

The swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), is a new addition to the pest complex found in crucifer crops produced in Ontario, Quebec, and New York State. The insect is native to Europe and Asia where it is considered a pest of cruciferous crops. Swede midge was positively identified in Ontario in 2000, although damage symptoms in cole crops consistent with infestation have been noted since 1996.

Quarantine pest

Counties with known populations within Ontario and Quebec are presently under quarantine. Swede midge was detected for the first time in Niagara County, New York, during the summer of 2004. Table 1 lists counties with known swede midge infestations.

Counties with identified populations of swede midge (2004)

• Ontario
  • Brant
  • Dufferin
  • Durham
  • Halton
  • Hamilton-Wentworth
  • Niagara
  • City of Toronto
  • Victoria
  • Waterloo
  • York
  • Simcoe
• Quebec
  • Communauté Urbaine de Montréal
    
  • Laval
    
  • La Vallée-du-Richelieu
    
  • Vaudreuil-Soulanges
• New York State
  • Niagara County (2004)

The Canadian Food Inspection Agency (CFIA) quarantine restricts the movement of swede midge host species and the soil associated with the plants. Horticultural producers in these municipalities cannot transport any host plant species (transplants, finished live plants, soil) to non-quarantined municipalities within Ontario, Quebec, the rest of Canada or the US without certification by the CFIA. Brokers, shippers and wholesalers are similarly regulated. Currently, there are no phytosanitary requirements or restrictions on the movement of produce.

Details of the CFIA Directive D-02-06 "Interim Phytosanitary Requirements to Prevent the Entry and Spread of Swede Midge (Contarinia nasturtii)" can be found on the CFIA website.

Challenges

Identification

Identification of swede midge is not an easy task. Damage is readily mistaken for common physiological (heat or frost stress) and/or nutritional problems (molybdenum deficiency) found in crucifer fields. Insect feeding by other pests (e.g. flea beetles, tarnished plant bug, caterpillar complex) can leave similar scar tissue and damage to growth points; nicking young plants while cultivating can result in multiple heads and the formation of scar tissue on crucifer stalks. A single "symptom" in the field is not cause for definitive diagnosis of swede midge infestation! Symptoms include:

• Swollen, distorted or twisted young shoots and leaf stalks
  
• Blind head (death of main shoot / growing point)
  
• Crinkled, crumpled and asymmetrical heart leaves (drawstring effect)
  
• Brown scarring along petiole or stem
  
• Multi-stemmed plant (cabbage topping)
  
• Swollen and closed flower buds
  
• Premature bolting
  
• Riciness of cauliflower
  
• Presence of secondary bacterial rots

The swede midge does not restrict itself to one growth stage in a crop, so any young growing tissue on a plant is at risk. Damage can occur at any time throughout the season (e.g. from the seedling stage through heading). Swede midge populations can build up on the secondary shoots of otherwise healthy looking crops and on plants remaining in the field after harvest.

Swede midge adults are tiny (1.5-2 mm), delicate flies that are difficult to see in the field. Specimens caught on sticky cards are almost impossible to distinguish from the other 60+ Contarinia species present in Ontario. Eggs are invisible to the naked eye. Remember: Larvae (3 mm and yellow-white when mature) must be found in association with symptomatic plants in order for the CFIA to deem a production area "positive" for SM - this is extremely important from a quarantine standpoint.

Life cycle

The swede midge pupates in the soil to complete its development in the spring. Research in Ontario indicates that the entire overwintering population of swede midge does not emerge synchronously in early spring, but rather in three distinct peaks through the month of June. In Ontario, there appear to be 3 to 5 main population peaks per year. Adults emerge continually from the end of May until the middle of October, thus ensuring a long-term battle with the pest. Cooler temperatures (20-25°C) and adequate rainfall provide perfect conditions for development. After emergence, adults mate within 12 hours. Females will fly to nearby host material and will lay up to 100 eggs, typically in small clusters. For this reason, several larvae are typically found in association with damaged plant material. The eggs hatch within 1-3 days. Larvae develop in a "liquid" environment consisting of their saliva and the breakdown products of the plant. They complete their development in 7-14 days, and then drop to the ground to pupate. If conditions are favourable, new adults will emerge 9-14 days later and the cycle will continue. During periods of drought, larvae in the soil may remain dormant, with growth resuming following rainfall or irrigation. The swede midge overwinters as a pre-pupa in the soil, but some may stay in the soil for more than one winter, making long-term crop rotation important.

Best Management Practices

Greenhouse Sanitation

Always start off right with clean transplant material. This applies not only to insect pests, including the swede midge, but diseases of cole crops as well. Be confident about the source of your transplants, and do not bring transplants from infested areas into clean areas unless the production facility is following the CFIA Swede Midge Certification Program (SMCP). Eighty percent of growers in Ontario produce their own transplants. The remaining 20% purchase transplants from four certified growers, all of which are located in an area where swede midge has not yet been identified (Kent County, CFIA surveys 2004). Growers of swede midge host species are strongly encouraged to participate in the CFIA SMCP, whether they are in a quarantined municipality or not. For information on the specific requirements of the SMCP, see the CFIA website.

Research is underway to register insecticides for use in the greenhouse against swede midge. Tristar 70 WSP (acetamiprid) has been granted an emergency registration for the control of swede midge on greenhouse transplants of Brassica Leafy Vegetables. Please refer to the label for specific information on the use of this product. Inspect all transplants prior to planting, particularly in known areas of SM infestation. When hardening off young seedlings outside, cover them with fine netting or a floating row cover to prevent any egg-laying activity.

Crop Rotation

Crop rotation is the single most effective way to manage swede midge populations in the field. With multiple generations (up to 5 in Ontario) and a high reproductive potential, swede midge populations can build up very quickly under continuous production of a host crop. A small number of swede midge adults in the first generation can give rise to tens of thousands by the third generation in July! By late September, high numbers of overwintering swede midge larvae create challenging management issues for the following growing season.

Swede midge may survive in the soil for 2 or more years; therefore, a crop rotation that does not include crucifer crops (or any other member of the Brassicaceae family) is essential. Trials in Europe indicate that high infestations were reduced to economically acceptable levels for several years following a 2-year crop rotation. Much higher damage has been observed in multi-cropped cole crop fields. Depriving the swede midge of host plant material through crop rotation provides an effective and ecologically acceptable management technique.

Preliminary work in Ontario (2004) illustrates the importance of a host-free period to swede midge population dynamics: In areas previously under continuous production of susceptible cole crops and then planted to soybeans or corn (non-host crops), swede midge continued to emerge throughout the following year.

Swede midge from old fields present a season-long threat to neighbouring cole crops.

We recommend a minimum 3-year crop rotation, recognizing that for many growers, this presents a major challenge from the standpoint of available land base and continued access to markets.

How far away does the field need to be? Some European data suggests a minimum of 200-300 m between sites; distances of up to 1 km have been proposed. We lack the data to provide a science-based answer, but caution dictates that new plantings should be far enough (~ 1 to 2 km) to prevent the possibility of SM being carried into the field by a light wind. Without a host crop nearby, the SM female will not be able to find a place to lay her eggs in her short 3-4 day life span.

Field Selection

Swede midge is considered a poor flyer. Growers with swede midge populations have found less damage when they plant crucifers in open fields. Damage symptoms are typically first observed in the field along tree-lines, buildings and hedge rows, because the insect is easily blown into these areas. Planting in isolated areas, up from prevailing winds, may help decrease the risk of spread.

Crop Selection

The swede midge will attack most members of the Brassicaceae family, with highest levels of damage reported on broccoli, Chinese broccoli (gai lan), Brussels sprouts, cauliflower, and Chinese cabbage (choy sum). The broccoli variety "Paragon" is highly susceptible to swede midge damage and should be avoided in infested areas. "Everest" and "Triathlon" are less susceptible than some other broccoli varieties. Canola is readily attacked. All Asian crucifers are susceptible to swede midge damage. Cruciferous weeds including field, wormseed, dog and wild mustards, Sheperd's Purse, field pepper grass and others are also hosts and may act as reservoirs for swede midge populations in the absence of cole crops / canola.

Field Sanitation

Remove and / or control all Brassicaceae weeds including field mustard, wild mustard, dog mustard, Shepherd's Purse, stinkweed, etc. - these are all alternate hosts for swede midge. Deep plowing and chopping infested residue will help to disrupt the SM lifecycle because the majority of SM overwinter in the top 5 cm of soil and emerge the following spring.

Planting and Harvesting Dates

Planting only early season crucifer crops is another control strategy to reduce damage levels and population growth. The amount of damage is directly related to the plant growth stage at the time of attack.

The younger the plant when attacked, the more severe the damage.

As plants grow, damage becomes increasingly evident. The first emergence of swede midge occurs from mid to late May. Damage to early plantings will be less severe than to late plantings because the plant development will be advanced by mid-July when high populations occur. Harvesting of early season crucifers begins in July, which minimizes the amount of damage to the crop. Avoidance of late season crops will also help to reduce the size of the overwintering population in your fields. This strategy will not work for long season crucifer crops like Brussels sprouts.

Monitoring / Scouting

Do not assume that you have an established population of swede midge on your farm, but be on the look-out for signs and symptoms, particularly if you are located within an infested county. Early detection of swede midge is key to maintaining pest populations at manageable levels. Familiarize yourself with the information provided in various OMAFRA resources.

Attention should be paid to sheltered areas, along field edges and buildings. Swede midge adults are not strong fliers and tend to prefer areas of low wind movement. Alternate weed hosts in these areas should be inspected. Examine young crop plants for unusual growth habits, with emphasis on the growth point and any side shoots. Check young plants for galls at the growth point and for swollen leaf bases. Brown, corky scarring is a key diagnostic feature, indicating larval feeding. Infested plant material often has a "moist" or "wet" appearance where larvae are actively feeding.

Once a suspect plant is found, new growth should be carefully examined for the presence of larvae. Larvae can be seen with the naked eye or a hand lens. If larvae are not found, place the suspected plant material in a vial of rubbing alcohol and shake; typically, the larvae will come right out of the plant material. You can also put plant material in a plastic bag and let it sit for a while; in the heat, the larvae will leave the tissue and can be seen crawling around. If no larvae are found, they may have already dropped to the soil to pupate. So keep looking!

A pheromone trap tested in 2004 is now available commercially. It is possible for consultants/growers to order swede midge pheromones, traps and liners from Switzerland. The distributor is Andermatt Biocontrol, Switzerland, and the email for them is sales@biocontrol.ch taken from their website. These traps are highly species-specific and will trap swede midge males at low population densities, making monitoring, identification and timing of spray applications a much simpler task. With proper training, swede midge males can be distinguished from other insects caught in pheromone traps.

Insecticide Spray Timing

Well-established thresholds have not been determined for swede midge. In the absence of a commercially available pheromone lure, timing insecticide sprays has been difficult at best. Research trials planned for 2005 will incorporate pheromone trap data to address the issue of threshold; preliminary data from 2004 indicates growers may have opportunities to optimize their spray applications.

Growers with known local populations of swede midge are advised to initiate a pest control program incorporating both cultural and chemical management. Transplants should be protected as soon as they are removed from the greenhouse, or immediately after planting. Management of early swede midge populations will reduce the potential for a population explosion by the end of the season.

In 2005, only two products are registered for use against swede midge in the field: Matador 120 EC (lambda-cyhalothrin) and Assail 70 WP (acetamiprid). Matador is a synthetic pyrethroid targeted towards adults. Although the product is not systemic and will not control larvae within the plant, Matador 120 EC has demonstrated good residual efficacy and confers up to 10 days protection in the field. Assail 70 WP is locally systemic and is effective in managing larvae within the plant. Please read the product labels for additional information on rates, PHI and application.

With a limited tool-kit, the development of resistance to the available insecticides is a serious concern. Choose and use products wisely. Research teams in Ontario, Quebec and New York are working collaboratively towards the evaluation and registration of additional insecticides for use in both the field and greenhouse.

The Ontario Swede Midge Research Team (OMAFRA - Fraser, University of Guelph - Hallett, Sears and Pitblado) will provide information on adult flight activity from data collected with pheromones and other traps. Timely reports will be posted in "HortMatters" in 2005. If you are a grower within an infested production area, be sure to subscribe to this electronic publication for weekly updates on swede midge activity.

Final Thoughts and Take Home Messages

The swede midge is an unwelcome guest who is unfortunately here to stay. Once on your farm, this insect will be virtually impossible to eradicate. No single strategy will provide 100% control of swede midge. With proper management that incorporates all cultural techniques and sound chemical practices, populations can be kept at levels low enough to avoid economic injury. Pheromone traps are critical to the development of IPM programs for timing applications of pest control products. Despite recent positive finds in the US, swede midge will likely remain a quarantine pest for the foreseeable future. Surveys incorporating pheromone traps will likely identify other infested areas within Ontario, Quebec and the US.

Your swede midge management plan should include:

1. Using clean transplants
   
2. A 2 to 3 year crop rotation to non crucifer crops
   
3. Monitoring/Scouting for swede midge detection
   
4. Field sanitation and residue management
   
5. Selection of less susceptible cultivars - avoid swede midge favourites
   
6. Early planting to avoid / prevent high populations
   
7. Field selection - use open fields where possible
   
8. Preventative insecticide applications as required

This BMP document was developed by the International Swede Midge Task Force Membership:

• Ontario Ministry of Agriculture and Food (OMAFRA): Kristen Callow (past Chair, formerly of OMAFRA), Hannah Fraser and Graeme Murphy
• University of Guelph: Dr. Rebecca Hallett, Dr. Ron Piblado and Sheila Goodfellow (MSc. Candidate)
• Cornell University: Dr. Tony Shelton
• Cornell Cooperative Extension: Dr. Julie Kikkert and Christy Hoepting
• Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec (MAPAQ): Danielle Roy
• Canadian Food Inspection Agency: Louise Dumouchel (CFIA)
• Unites States Department of Agriculture (USDA-APHIS): Dr. Susan Ellis
• Swiss Federal Research Station for Horticulture: Dr. Robert Baur
• Ministère de l'Agriculture, de l'Alimentation, de la Pêche et de la Ruralit (MAAPAR-France): Dr. Jean Charles Maissoneuve

Related Links

• The Swede Midge - A Pest of Crucifer Crops, OMAFRA Factsheet, Order no. 08-007
• Swede midge factsheet - CFIA
• Andermatt Biocontrol, Switzerland
• OMAFRA Hort Matters Newsletter