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New Pest Amongst Our Berries

University of Minnesota Extension, Stearns County News
June 17, 2015

Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton & Morrison Counties


New Pest Amongst Our Berries
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (06/17/15) — Last summer did you bite into your home grown raspberries to only discover little white maggots? Gross! Sadly you likely found the larvae stage of an invasive vinegar fly called the Spotted Wing Drosophila, Drosophila suzukii. Although tiny, this pest can do a lot of damage to your raspberry, strawberry, grape, blueberry, and nearly all cane berries.

The Spotted Wing Drosophila (SWD) is an invasive pest that originates from Asia, was discovered in Hawaii in 1980, California in 2008, and has quickly spread throughout the United States. The Spotted Wing Drosophila was first discovered here in Minnesota in 2012 and each year is found in more counties.

The reason this vinegar fly is so damaging to berry crops is the female is able to use her sharp, serrated ovipositor to cut through the fruit’s skin and lay eggs inside the fruit. The larvae, aka maggots, then feed within the fruit causing brown, sunken areas that decay the berry. Infestation of the larvae often goes undetected at harvest and is not noticed until consumption when small white maggots are found in the fruit.  Consumption of the maggots is not harmful to humans, although not appealing.  From egg to adult, the life cycle occurs in as quickly as seven days. Multiple generations occur each growing season here in Minnesota, making it a challenging pest to control and causes expansion of infestation throughout the state.

The best management practices for the SWD begin with persistent monitoring as soon as fruit are set.  Traps should be constructed and set, and weekly inspection should occur which requires proper identification of the SWD. Key identifying characteristics include: 1/8-1/2 inch long, yellowish-brown color with red eyes. Males carry the name sake with clear wings that contain a dark spot on the first vein near the tip of the wing. Females have a clear wing but do not have the spot; instead a key feature is the serrated ovipositor, part of the fly near the rear used to insert eggs into fruit. A 30x magnifying hand lens will be needed to properly identify the serrated ovipositor verses other look-alike flies. The serrations look like large, dark colored teeth.

The traps can be constructed out of a 32 ounce plastic cup; some preliminary research indicates the flies are attracted to red. Put small 3/16-3/8-inch holes around the top of the cup, leaving a 3-inch area without holes for ease in pouring the bait. It is important to put these specific sized holes to eliminate non-desired species from getting inside, making identification more difficult. Pour one-inch of apple cider vinegar with a drop of dish soap into the cup. To help in proper identification, fasten a sticky card to a lid; sticky catch cards can be purchased at your local garden centers or online. Secure the lid onto the trap using tape and fasten a wire or string as well to serve as a way to hang the trap in your berry crops.  The trap should then be placed in a more shaded area in the fruit zone; the SWD seems to avoid hot, full sun spots.

Check your trap at least once a week and if you identify the SWD, management practices should be implemented immediately. Good sanitation helps reduce high populations of SWD. Also, frequently harvest your berry crops to ensure ripe fruit are not left for extended periods of time. Remove all expired fruit; do not leave them on the ground.

Insecticides that have effectiveness on the SWD include: pyrethrum, spinosad, malathion, and bifenthrin. CAUTION: Read all insecticide label directions before buying and using. Be sure product is labeled for the specific crop you wish to treat.

For more information about the Spotted Wing Drosophila visit: http://www.fruitedge.umn.edu/spotted-wing-drosophila/swd/
 
Right: Male Spotted Wing Drosophila. Left: Female Spotted Wing Drosophila Ovipositor
Photos: Martin Hauser, California Dept. of Food and Agriculture

Contacts

Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
adam0062@umn.edu
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