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Japanese Beetle Management Updates for Apples - July 2019

Annie Klodd, Bill Hutchison, Eric Burkness, and Dominique Ebbenga

For an introduction to Japanese beetles, read:

Review of Pesticide Options

Adult Japanese beetle. Photo: Jeff Hahn.
Japanese beetles release an aggregation pheromone to attract others. Therefore, early control is important to reduce aggregations (“feeding frenzies”) of beetles on trees. Several repellants and anti-feedant products work by slowing aggregation, and have residual activity between 2-3 weeks:

  • Neonicotinoids: Assail, Belay, Wrangler/Alias/Montana (Actara is not as effective, and has a 35 day PHI) 
  • Neem oil: Does not effectively kill adults, but will reduce immigration into the orchard (can be tank-mixed with a conventional insecticide). Apply in the evening or night, not in the middle of the day.
Aside from Assail, the above products do not provide immediate knockdown of Japanese beetles. For immediate knockdown of beetles, one of the following may be applied:
Imidan (phosmet)
BeetleGone (Bt)
Mustang Maxx or other pyrethroids, which indeed give immediate knockdown

Assail is also effective on 2nd generation coddling moth, so growers may choose to wait to spray this for JB until the 2nd gen. coddling moth are active, as to target both at once.

Several pyrethroid and carbaryl products are effective on JB but also kill biocontrols and parasitic insects (Imidan is a nasty product and also kills beneficials). For example, they target predaceous mites that feed on European red mite and spider mites, increasing the occurrence of those pests. These products include Asana, Baythroid, Danitol, Warrior, Proaxis, Mustang Maxx, and Sevin.
Some growers are currently spraying for leaf hoppers and aphids. These products may have some effectiveness on JB, but more potent products like those listed above are preferred.

Organic options: As stated above, Neem can be used as a repellent, and Bt (BeetleGone) provides knockdown. Pyganic and Entrust (spinosad) may also have effectiveness on Japanese beetles in apples.

Current 2019 Japanese beetle trap counts

As of July 19th, the following locations were averaging the following beetle densities:
Forest lake (berry patch):  40/trap
Hastings:  99/trap
HRC (Arboretum):  239/trap
Rosemount:  ~2905/trap

According to Bill Hutchison’s research group at UMN, it is possible that sandier soil may be less conducive to JB overwintering sites. The soil at the Hastings trap site, with the lowest JB counts (above) is 72% sand; Rosemount, with the highest trap counts, is 15% sand. This is only preliminary data, and geography may also be contributing to the differences. It is also important to remember that JB travels long distances, and the soil type on a particular farm will not prevent adult beetles from immigrating onto that farm. 

Other Management Considerations

Female JB have difficulty laying eggs in long grass. Keeping grass over 3 inches may help decrease egg laying within the orchard. Other adults will still fly in from other areas, but this is a simple way to potentially reduce JB numbers without extra cost or inputs.

Some growers have been spot spraying individual trees where JB are observed. While this helps reduce pesticide input and threat to beneficial insects, it also leaves many trees vulnerable to JB infestations as populations easily fly between areas of the orchard.

Another option to consider, which would also save on overall insecticide sprays, is border treatment.  During the initial colonization of an orchard, JB adults will often start their feeding on the edge trees, also known as a classic “edge effect.” Although UMN is still testing the longer-term, seasonal benefit of border/edge treatments, this is something growers can also experiment with.

Researchers at several universities are studying variety preference of JB in several fruits. Anecdotally, it seems to have a strong preference toward Honeycrisp, but much more research is needed. UMN researchers would like to acquire grant funding to study variety preference in apples. Grower input is needed in order to acquire grant funding.

UMN Pesticide Trial 2019 (on raspberry)

Hutchison's research group is conducting a raspberry pesticide trial for Japanese beetles, to determine product effectiveness and recommendations for best use. In the current trial, they are comparing Sevin (carbaryl), Entrust (spinosad) and Mustang Maxx (pyrethroid). Before spraying across all plots, the pre-trial count average was 27.6 JB adults per meter of row. Plots were 3 rows wide by 10 ft long and sprayed on July 18th with 25 gallons of water per acre on both sides of the row with a CO2 backpack sprayer and a 3 ft boom.

1 day after treatment (DAT), July 19th, the counts were as follows:
Sevin XLR Plus 64oz/ac = 0.0 JB per meter of row
Sevin XLR Plus 32 oz/ac = 0.0 JB
Mustang Maxx 4 oz/ac = 0.0 JB
Entrust 6 oz/ac = 4.5 JB
Untreated check  = 12.0 JB

4 DAT, July 22, counts:
Sevin XLR Plus 64oz/ac = 1.5 JB per meter of row
Sevin XLR Plus 32 oz/ac = 1.0 JB
Mustang Maxx 4 oz/ac = 0.75 JB
Entrust 6 oz/ac = 5.75 JB
Untreated check  = 11.75 JB

This trial is ongoing, and data will also be collected at 7 DAT. After Sevin and Mustang Maxx treatments, the beetles will visit the plants as new adults emerge from the soil, but typically they won't feed much or at all; occasionally a dying adult is found as well, on 4 DAT. Populations will likely build at 7 DAT as the residual control fades.

Defoliation Activity: Is It As Bad As It Looks?

For the photos below, guess the percentage (%) of each leaf that has been defoliated (chewed away by Japanese beetles). The answers are below the last photo. 

Photo A

Photo B
Photo C
Answers: Photo A) 2.1%. Photo B) 6.8%. Photo C) 10%. Are these numbers surprising to you? Because there are no established control thresholds for JB defoliation, the management implications of identifying defoliation amounts are currently limited. However, the take-home message is that while it may look like a JB population is devastating a tree, there is likely more healthy, photosynthesizing tissue than it appears.

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