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Spotted Wing Drosophila and Japanese Beetle Management Updates

Japanese beetles congregate on newly emerged grapevine leaves. Photo: Annie Klodd.

This article discusses current spotted wing drosphila and Japanese beetle trap counts for Minnesota locations, and gives an update on research for management of Japanese beetles.

Spotted Wing Drosophila (SWD) 

Adult SWD captures continued to increase at most locations this past week. Although blueberries are inherently less vulnerable to SWD egg-lay (and larval damage) compared to raspberries, growers should remain diligent in monitoring all berry crops and using insecticide (organic or conventional) sprays for berry protection.

Trap numbers this past week ranged from a high of ~200 per trap at Forest Lake (summer raspberry, blueberry), 150 per trap at Hastings (wine grapes), 125 per trap at the Horticultural Research Center, Chanhassen (all berry, fruit crops), and 100 per trap at Rosemount (fall raspberry). As of 7/24, SWD flies were as high as 800/trap at Spring Grove, Houston County (mixed berry crops).

Although the cooler weather this past week likely slowed JB activity (see below), SWD population growth thrives in cooler weather (60-80F), and this has likely contributed to increased activity. SWD fly counts for our network sites are at FruitEdge SWD page. SWD trap catch numbers are updated weekly on Tuesdays. Comparisons are also available for 2018-2019.

SWD female (left), with close-up view of ovipositor (for egg-lay), and male (right) with characteristic dark spots on each wing (C. Gu├ędot, Univ. of Wisconsin).

As noted in previous articles, it is always best to have at least one or two traps on your farm, to track your on-farm SWD populations and thus have a much better idea of your risk of berry infestations. For more information on SWD traps, or how to build your own using apple-cider vinegar (ACV) traps, see this page. For more information on managing SWD, see this article from June 18.

Japanese Beetle (JB)

During the past two weeks, JB adult trap counts have leveled off quite a bit at the 4 primary monitoring sites for southern MN. Compared to low counts in mid-July, JB numbers as of August 4th have averaged >2500 adults/trap/week at Rosemount (UMORE Park), ~1,000 JB per trap at the Horticultural Research Center near Chanhassen, Carver County, 750 JB per trap at Hastings, Dakota County, and only 100 per trap at Forest Lake, Washington County.  As a reminder, JB counts can also be viewed 24/7 at the new FruitEdge, JB trap page.

Japanese beetles. Photo: Jeff Hahn, UMN Extension, Dept. of Entomology

As noted on this web page, we also provide 2019 JB trap catch data for these same locations, for comparison. Due to the more rapid increase in heat units or “degree-days”, JB numbers in 2020 began to increase 7-10 days earlier than in 2019. 

Key Japanese Beetle (JB) Management Update

Several fruit growers, whether conventional or organic-certified, must often rely on insecticide sprays to manage rapidly increasing numbers of insect pests, including JB adults. Although our research continues to develop objective economic thresholds to determine when management action is necessary, we are also conducting a new Insecticide Timing Study this year in fall raspberries, as part of a graduate student project (Adam Toninato, MSc).

Though the study is still in progress, we provide a brief summary below of the efficacy of 3 common products used for JB control, and labeled for raspberry (these products are approved/labeled for other berry crops as well). Sevin and Mustang Max performed as expected; but we have been surprised by the relatively low efficacy of Entrust (organic-certified product). This will continue to be studied.

*2nd spray was applied 2 weeks after 1st application. Before the 1st spray (7/9), the pre-treatment average number per meter-row = 20.7/plot. All sprays were applied to both sides of each row using 25 gal water/acre.
**1-DAT = one day after 1st spray; 21 DAT = 20 days after 1st spray.

Data continue to be analyzed; final results, including collection of marketable yield data, may vary depending upon final statistical analysis.

An overview of JB management in fruit crops, via Michigan State, is available here.

Note: For updated insecticide control options, refer to the annually revised Midwest Fruit Pest Management GuideThis guide is produced by UMN Extension and cooperating Midwest state Extension Specialists. For all pesticides, it is essential to read the label prior to use, and to closely follow the Re-entry Interval (REI) and Post-harvest Interval (PHI) requirements.

Authors: Bill Hutchison, Eric Burkness, Suzanne Wold-Burkness, UMN Extension IPM Program, & Adam Toninato, Graduate Student, Dept. of Entomology, UMN.

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