Hello,

Japanese beetles likely cause the brown skeletonized leaves on your Murray Birch trees. These beetles are known to feed on the leaves of more than 300 species of plants, including birch trees, leaving them skeletonized. More information at these links:

Japanese beetles in yards and gardens | UMN Extension

Japanese Beetles in the Urban Landscape (purdue.edu)

Japanese beetle: Tips for your lawn (msu.edu)

To manage Japanese beetles while avoiding pesticides, especially considering your native pollinator garden, you can consider the following non-chemical control methods:

Handpicking: This is effective when beetle numbers are low. You can handpick or knock the beetles into a bucket of soapy water early in the morning or late in the evening when they are less active. More information at these links:

Japanese beetles in yards and gardens | UMN Extension

Japanese Beetle Management Without Insecticides – Wisconsin Fruit

Row Covers: For small trees or shrubs, you can use fine netting or row covers to physically prevent the beetles from reaching the leaves during their most active period in July and August. More information at this link:

Japanese Beetle Management Without Insecticides – Wisconsin Fruit

Traps: Traps baited with floral and pheromone lures can attract and capture Japanese beetles. However, they should be placed away from the trees as they can attract more beetles to the area. More information at this link:

Japanese Beetle Management Without Insecticides – Wisconsin Fruit

Biological Control: Certain products like neem oil can act as repellents. Neem oil doesn’t kill the beetles but can reduce their immigration into the area. It should be applied in the evening or at night. More information at this link:

Japanese Beetles: Choices for Conventional and Organic Insecticides (umn.edu)

Mass Trapping: Research has shown that mass trapping systems involving a double lure system can protect plantings from Japanese beetles. More information at this link:

Organic Management Options for the Japanese Beetle at Home Gardens // Missouri Environment and Garden News Article // Integrated Pest Management, University of Missouri

It’s important to monitor beetle activity and tree health regularly to determine the effectiveness of these methods and make adjustments as needed. Remember, early intervention can help prevent severe damage.

I hope this helps!