The Dreaded Japanese Beetle (Again)

Despite winter and spring conditions that we hoped could thwart them, the Japanese beetles are at it again. They fall on us as we mow beneath trees, eat our hard-won fruits as they multi-task, and drown in the dog’s water dish.  Here are some important considerations:

▪Japanese beetles do lay their eggs in the soil.  Managing Japanese beetle grubs to stop the damage to turfgrass IS effective. Targeting grubs IS NOT an effective means of damage prevention to trees, roses, and grape vines.  This is because there are ditches, fence lines and creek banks that are never treated for Japanese beetle grubs and emerging adults will always fly to where there is food.

▪Be aware that insecticide applications to anything with flowers on it will kill pollinators too.

▪For safety reasons, insecticide applications to food plants MUST be labeled for use on edible crops and the pre-harvest interval (PHI) followed.

▪It’s illegal to spray any systemic insecticide on trees. Systemic products are those taken in by plant tissues and distributed throughout the body of the plant.  The restricted-use insecticide chlorantraniliprole is effective against Japanese beetles but does not harm pollinators. Consider a tree service to apply chlorantraniliprole to trees as beetles emerge in June.

▪Japanese beetle feeding slows in August and plant damage decreases.  Yes trees do look lacy right now, but fortunately they do not die from Japanese beetle defoliation.

▪Japanese beetle traps are TOO good at drawing in JB. There are more Japanese beetles doing damage to plants in yards with traps than those without.

▪If collecting Japanese beetles from plants, the best time of day to do so is 7:00 in the evening. Collecting them at 7:00 results in a lower population of JB than at any other time of day. (Thank goodness for grad students who do the tedious work of collecting the data!)

▪Japanese beetles do not, I repeat do not, emit an aggregation pheromone.  An insect aggregation pheromone is an odor that is emitted to broadcast “supper at the Smith house.”  Rather, it is the plants emitting distress pheromones that draw JB to feast there.

So there you have it.  Japanese beetles are abundant, there is no one-size-fits-all remedy for managing them, and they tend to make plants look bad but not kill them. We take our lumps with gardening, along with the good.

Kathleen Cue
Horticulture Educator at Nebraska Extension
Kathleen serves as the Horticulture Educator for Nebraska Extension in Dodge County. She educates people on making smart plant choices to reduce use of fertilizers and pesticides in their landscape which has a positive impact on air, water, soil and environmental quality, property values and people’s pocketbooks.

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