Japanese Beetles

Japanese Beetles

In Eastern Ontario, Japanese beetles have recently been identified as a significant new pest. The damage this particular beetle is known to cause has created concern for local authorities and gardeners alike. Measuring 10-12 mm in length, these beetles can be easily identified by their metallic green bodies and coppery-brown wing covers. In mid and late summer, they feed on the fruits of many tree species, which escalates their damage. Gardeners and arborists alike have expressed worry over the trees that are becoming infested and therefore dying gradually. One of the most notable symptoms that I have seen in a number of infested plants is the skeletonization of leaves. This is a process during which the soft tissues that exist between the veins of a leaf are consumed, leaving a lace-like pattern. This symptom is highly indicative of a heavy infestation and the strangulation of the beetle. In these severe infestations, the feeding has escalated to the point at which severe defoliation has occurred. This is not only the death of leaves but the complete stress of the tree to the point that its ability to resist other diseases is weakened.

The damage caused by the Japanese beetle can be mitigated if the appropriate action is taken early enough. Continuous monitoring of the trees during the active beetle season can significantly decrease the chance of severe infestations. With infested trees and small infestations, physical control methods such as handpicking beetles and dropping them into soapy water are practical. The use of Japanese beetle traps can reduce the local beetle populations, but can, in some cases, increase the beetle population in the area. Proper placement of the traps is mandatory for ensuring the protection of more valuable trees. Proper tree care and maintenance, such as adequate watering, mulching, and fertilization, not only protects the trees against these beetles but also strengthens the trees.

If a tree is severely infested, more drastic treatment can be required. Treatment with insecticides registered for control of Japanese beetles will kill some beetles, but should be done at the right time—when adult beetles initially become visible for optimal control. Call a licensed arborist or pest management professional to choose suitable materials and techniques, particularly for large, valuable trees. After treatment in all situations, ongoing monitoring and maintenance are critical to aid tree recovery and reduce further damage.