Pest Alert: Swede Midge in New York State (October 14, 2004)

On September 20, 2004, two Swede midge (Contarinia nasturtii) specimens from Niagara County, New York, were trapped in experimental pheromone traps that Cornell Cooperative Extension Service is field-trialing in North America with the Swiss Federal Research Station for Horticulture. These are the first detections in the United States. Massachusetts will survey for swede midge in 2005 as part of the USDA Cooperative Agricultural Pest Survey.

The swede midge is native to Europe where it is a major pest of crucifer crops. The presence of the swede midge in North America was first confirmed in 2000 in Canada. The damage growers had seen since 1996 was mistakenly attributed to nutrient deficiency. No one knows how the swede midge reached North America or exactly how long it has been present in Canada. Swede midge has been found in 12 municipalities in Ontario and 1 in eastern Quebec.

Hosts: While swede midge will attack any member of the brassica family, the highest levels of damage have been seen on broccoli, Chinese broccoli (gai lan), Brussels sprouts, cauliflower, Chinese cabbage, and other Asian greens. Wild crucifers are also hosts for swede midge.

Lifecycle: Multiple (3-4) overlapping generations have been seen in the field in Canada with major peaks occurring during late June, late-July-early August, and late-August-early September. The swede midge overwinters as pupae in the soil and emerges in the spring. The adult is a small (1.5-2mm) light brown fly with hairy wings indistinguishable from other midges. Eggs are very small (0.3mm) and laid on the youngest parts of the plant (e.g. flowers buds, leaf bases) often near the growing point. Eggs are transparent when first laid and change to a creamy white color as they mature. The larvae feed in groups in protected areas of the plant tissue typically near the growing point for 10-12 days before dropping to the soil to pupate. Full-grown larvae are 3-4 mm long and yellowish in color. Adults can emerge from the soil for the next generation in two weeks depending on climatic conditions.

Damage symptoms: Damage symptoms are caused by larval feeding. Larvae secrete substances to break down the cell during feeding causing changes in the physiology of the plant. The following damage can be caused by the swede midge: brown corky scarring especially along petioles, distorted and twisted leaf stalks, death of the growing point resulting in a blind head, crinkled and crumpled heart leaves, deformed and asymmetrical heads, and multi-headed or multi-stemmed plants resulting from destruction of growing tip.
Swede midge damage can look like other common physiological, nutritional, and insect problems found in cole crops. One needs to find larvae within the plant to confirm swede midge is the cause of the damage. Examine suspect plant tissue with a hand lens or place the affected plant part in a black plastic bag in the sun for several hours to force the larvae to leave the plant tissue. Swede midge damage is most often found in areas sheltered from the wind such as field edges and buildings because the swede midge is a poor flier and prefers areas of low wind movement.

The pest alert is from the Massachusetts Introduced Pests Outreach Project, a collaborative project between the Massachusetts Department of Agricultural Resources and the UMass Extension Agriculture and Landscape Program aimed at preventing the establishment of new pathogens and pests in Massachusetts. Visit the project website (http://www.massnrc.org/pests) for more information on Swede midge and other emerging pests or to subscribe and unsubscribe for pest alerts.