Pest Alert - Spotted Winged Drosophila

Update by Jaime Pinero, LU IPM Program.  For the latest information keep checking the website - http://www.LU-IPM.net

On June 6^th, 2014, we received the report that the first Spotted Wing Drosophila (SWD) male has been captured by a monitoring trap deployed on an early-season blueberry cultivar in the Webb City area. Farmers in the region are advised to start monitoring for this pest in their own orchards and fruit patches and apply a control measure if SWD is detected.

Male on left.  Female on right.

Should I spray insecticide against SWD again after a rainfall?

Research has shown that the amount of rain that occurs right after the application of some of the main insecticides used against SWD affects the durability of the insecticide on the fruit. For example, Dr. Rufus Isaacs (entomologist at Michigan State University) and his team have documented that Malathion effectiveness decreases immediately one day after a rain greater than 0.5 inches; the effect was that SWD control was only around 20 percent of the control in another field not exposed to the rain. This means that Malathion’s efficacy was almost lost after 0.8 inches of rainfall. In their trials, after a 0.8 inch rainfall, Lannate 90SP kept nearly all of its effectiveness even after 7 days, whereas Mustang Max lost about 20% efficacy within 7 days after the rain event. In general, a 2-inch rain one day after the application will substantially reduce the effectiveness of most of the products.

Remember, the label is the law, so if it doesn't prohibit re-application a farmer can go back again in with a particular insecticide she/he may have applied before a rain event. Otherwise, she/he will need to switch products. Some products explicitly state that farmers need to wait a week or some other period between applications.

As an example, the label of Malathion 8F (Gowan, 79.5% active ingredient) has these comments for blueberries:

·         The maximum application rate is 1.25 pints of product per acre

·         The maximum number of applications per year is 3

·         The minimum re-treatment interval is 5 days

The take-home message is that if rainfall occurs after insecticide application, re-application is needed to maintain fruit protection, but check the product’s label.

If you are a commercial berry / grape producer, the 2014 Midwest Small Fruit and Grape Spray Guide (freely available as PDF in this URL: https://ag.purdue.edu/hla/Hort/Documents/ID-1saa69.pdf) lists the following products against SWD for use in blueberries: Brigade WSB (10WP), Danitol 2.4EC, Delegate 25WG, Entrust 2SC (organic), Entrust 80WP (organic), Imidan 70W, Lannate LV, Lannate SP, Malathion 8F, and Mustang Max 0.8EC.

No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.

If you are interested in monitoring for SWD at your farm, free traps and bait (purchased using funds provided by a grant from the Missouri Department of Agriculture to the Lincoln University IPM program) are available. They can be mailed at no cost to you. Please contact Jacob Wilson at (573-681-5591).