Japanese beetle numbers continue to increase in the weekly trap counts conducted by University of Minnesota researchers in Forest Lake, Hastings, Chanhassen, and Rosemount. As infestations increase on farms, growers should be vigilant about control in order to prevent extensive leaf damage.
Review of Pesticide Options for Japanese Beetles
Japanese beetles release an aggregation pheromone to attract others. Therefore, early control is currently recommended to reduce JB aggregations (or “feeding frenzy” congregations) on apple trees and small fruit crops. Although research is underway this summer to determine economic thresholds for when to control JB in both raspberry and wine grapes, it will be at least another year before we have definitive results on spray timing recommendations to continue to build sustainable IPM and organic management programs.
Regarding insecticides, and beyond efficacy, do not rely on only one chemical for insect control. Rotate products with different modes of action to reduce the risk of resistance development.
Several repellents and anti-feedant products work by slowing the congregation of beetles, and have residual activity of 2-3 weeks. This means that they should be applied every 2-3 weeks based on scouting. These products include:
- Neonicotinoids: Assail, Belay, Wrangler/Alias/Montana. Actara is not as effective, and has a 35 day pre-harvest (PHI) interval.
- Neem oil: Does not effectively kill adults, but is a repellent that reduces immigration into the orchard. Apply neem oil in the evening or night, not in the middle of the day.
With the exception of Assail, the other products listed above do not provide immediate knockdown (death) of Japanese beetles. For immediate knockdown of beetles, one of the following may be applied:
- Imidan (phosmet)
- BeetleGone (Bt)
- Carbaryl (i.e. Sevin)
- Pyrethroids (i.e. Mustang Maxx, Danitol, Baythroid, Warrior)
Assail is also effective on 2nd generation coddling moth, so growers may choose to wait to spray this for JB until the 2nd generation coddling moths are active in order to target both at once.
While pyrethroid and carbaryl products are effective for immediate knockdown of JB, they also kill most beneficial insects such as parasitic wasps that help control aphids and other pests. 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.
Organic pesticide options:
Entrust provides partial control of Japanese beetles – see the 2019 trial data below. Pyganic (pyrethrum), Surround (kaolin clay) and BeetleGone (Bt) are additional organic options that provide varying levels of control. As stated above, neem oil can be used as a repellent for partial control as well.
Challenges: We understand and respect the desire of growers to use organic insecticides when possible. With that in mind, growers should consider whether the use of certain organic products for Japanese beetles really provides the environmental and safety benefits they are looking for, before applying them. Most organic products effective on JB still kill off-target beneficial insects like pollinators and still require protective equipment to prevent potential injury to the applicator. Additionally, organic products have short residuals (1-2 days) and must be re-applied very frequently for satisfactory control. Frequent application leads to increased fossil fuel use and becomes very expensive over the season. On the plus side, they have very short pre-harvest intervals and allow for harvest shortly after application.
For more details on organic insecticides for JB, see this article from Michigan State, in the section titled “Short PHI and Organic Options.”
Other Management Considerations
According to Dr. Bill Hutchison’s research group at UMN, it is likely that sandy soils are less conducive to JB overwintering by the larval (white grub) stage. For example, the soil at the Hastings trap site is 72% sand, and continues to have the lowest JB counts, compared to all locations sampled to date. Rosemount, with the highest trap counts, is only 15% sand. This is only preliminary data, and geography and the amount of turf habitat may also be contributing to the differences.
It is also important to remember that JB adults can travel long distances, and the soil type on a particular farm will not prevent adult beetles from immigrating onto that farm. The degree to which this happens, depends on farm size, the % sand on a farm, and the relative attraction of fruit and other crops, and wild hosts (such as wild grapes) on a given farm. The landscape analysis of JB dynamics continues.
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. Unfortunately, keeping grass long can promote other issues, like increased SWD habitat and retention of wet conditions that promote disease.
Spot spraying: Some growers have been spot spraying individual trees, or field edges, 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 these beetles easily fly between areas of the farm. However, this practice should continue to be practiced to “slow the spread”, depending on each farm situation.
Variety preferences: 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. Graduate student Hailey Shanovich (author of a F&V News article on BMSB in April) has been researching variety preferences and will be writing an article on her findings soon. — By Annie Klodd, Bill Hutchison, Eric Burkness, and Dominique Ebbenga. University of Minnesota Extension, University of Minnesota Entomology Department, and UMN IPM Program.