The Dreaded SWD Now Causing Extensive Fruit Damage in Missouri

Why do I keep blogging about this "bug" you ask?  If you have it on your farm, you know why.  If you don't have it on your farm, you're lucky.  I visited with a peach/cherry producer at a farmers' market last weekend.  The couple both work on the farm and have been farming all their lives.  They told me that the economic loss from the SWD has been devastating this year.  They also said that if next year is the same as this year, they'll get out of farming.  Needless to say that caught my attention.  So any chance I get, I will post about this invasive insect.  Here is a picture from the peach/cherry producers that they took of a female SWD positing eggs into a peach.

What is Spotted Wing Drosophila?
Spotted Wing Drosophila (SWD) is a small vinegar fly (about 0.1 inches in length) that for the last two years has been causing economic damage to berries, grapes, and softer-fleshed fruit such as peach in several areas of the US including the Midwest. It is native to Japan, so this insect is invasive to the US. SWD was detected in Missouri in late June through a monitoring system that was deployed by the LU Integrated Pest Management Program.

Why Should I be concerned about SWD? Is it that bad?
SWD very quickly became a devastating pest of berry crops in Missouri. Adults were first detected in monitoring traps in late June, 2013. By early August, infestations to blackberry fruits had already been reported. By mid August, SWD was reported infesting crops state-wide. In addition to small fruit crops, this invasive insect pest also attacks some stone fruits (cherry, nectarine, peach), high tunnel tomatoes, and wild hosts (including pokeweed, autumn olive, crabapple, nightshade, Amur honeysuckle, and wild grape). Raspberries, blackberries, blueberries, elderberries and grapes are at the greatest risk. Picture 1 shows larvae leaving out blackberry fruits.

 

How can I monitor for this pest?

It is very important that you learn how to monitor for this invasive pest. To determine whether SWD is present, the most effective and economical trap can be prepared using a clear plastic deli-type cup baited with a mixture of water (6 oz), dry active yeast (1/2 tablespoon), and sugar (as shown in Picture 2). Note the small holes that are made on the sides of the trap which allow flies to enter. A small yellow sticky card can be placed inside the cup so that flies that are attracted by the bait and enter the trap are retained by the card. This allows for easier fly identification.

 

How do I know whether flies trapped or active on fruits are SWD?
SWD flies look similar to the small vinegar flies that are typically found around or on fermenting fruits and vegetables. SWD males have one black dot on each wing and females do not have dots in their wings; they have a serrated egg-laying device called an ovipositor, to cut a slit into the skin of intact fruit to lay their eggs (Picture 3). This makes SWD a more significant pest.

 

How can I manage SWD in my farm or yard?

Below are some IPM options that can help reduce larval infestations by SWD: (i) Exclusion: For small plantings, one option is using a fine mesh screen with openings less than 0.98 millimeter (0.039 inches) wide (18 mesh or finer). Keep in mind that mesh screens will exclude pollinating insects, so it is best to cover your plants once fruit is set. Other SWD management options include (ii) Canopy Management: Thin the plant row to 3-4 strong canes per square foot, eliminating weaker shoots and opening the canopy.  Consider a trellising system that similarly opens the canopy. This may make plantings less attractive to SWD and will improve spray coverage and (iii) Sanitation: Removing over-ripe fruit from production areas as soon as possible can minimize SWD egg lay and larval development. Growers in other regions of the country have sent pickers through fields with one container to collect good fruit and another container to collect over-ripe fruit, again, to minimize egg-laying and larval development sites.

This article does not discuss insecticide options. A Fact Sheet on IPM options for SWD including effective organic and conventional insecticides is being developed by the LU IPM Program.

(by Dr. Jaime Pinero, LU IPM Specialist)