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Fruit Insect Pest Update - August 14, 2020

Spotted Wing Drosophila (SWD) 

Adult SWD captures remained high at most locations this past week; with captures at Forest Lake “exploding” to 1000 to 2000 SWD/trap (10-fold higher than last week). At Rosemount and Hastings, numbers increased to 200-300 SWD/trap. At all sites, summer raspberry is particularly vulnerable to attack at this time, and fall raspberry will soon be a concern as well. For these crops, high-tunnels fitted with fine nylon mesh continues to be the best management option. Where netting is not available, insecticidal protection will be necessary for most crops, since given the high numbers. For details on SWD trap numbers this past week, view the SWD page at the FruitEdge SWD page. SWD trap catch numbers are updated weekly (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. Guédot, 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: 

Japanese Beetle (JB)

JB adult counts continued to decline this past week at each of our monitoring sites in southern MN. Compared to low counts in mid-July, JB numbers as of Aug. 11th ranged from a low of 50 adults/trap/week at Forest Lake (Wash. Co.) to a high of 1500 JB/trap/week at Rosemount (UMORE Park). That said, actual defoliation levels have leveled off at most locations with defoliation  <15% in fall raspberries at Rosemount and Forest Lake. Overall JB pressure this year, at most locations, has been lower than 2018-2019. As a reminder, JB counts can also be viewed 24/7 at the new FruitEdge JB trap page.

Japanese beetles (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. As noted this year, 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) IPM Update 

Varietal impacts on insect pests (as well as disease resistance) should also be considered when developing a pest management program. As noted in previous years, JB adult feeding damage on raspberries varied considerably among three of the more popular varieties. As noted in recent years, we again found the preference this year on raspberry (high to low) to be: Prelude > Heritage > Nova. These results are based on field data for both JB numbers per variety, as well leaf defoliation levels for each. More results will be presented in future issues regarding varietal results for several popular wine grape hybrids.

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

Note: For annually updated insecticide control options, refer to the annually revised Midwest Fruit Pest Management Guide.

This 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.

Bill Hutchison, Eric Burkness, Suzanne Wold-Burkness, UMN Extension IPM Program, Dept. of Entomology, UMN

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