Dear Master Gardner: I haven’t seen any Japanese beetles this year. Have they somehow been eradicated?
Answer: Wouldn’t that be wonderful! Unfortunately, Japanese beetles, an invasive species, have not been eradicated. The Japanese beetle has been found in many Minnesota counties, but is only abundant in the Twin Cities metropolitan area and southeast Minnesota. Adult Japanese beetles start to emerge in late June or early July. They feed primarily in July and August. A good time to manage them is in the morning when they are moving slower. Pick them off or flick them into a bucket of soapy water. Leave them alone if you see a white spot on their head or back that seems out of place because this means they have been parasitized by the Winsome fly. According to the University of Minnesota Entomology Department, the Winsome fly was introduced as a biological control agent in 1923 in New Jersey, six years after the accidental introduction of the Japanese beetle. The Minnesota Department of Agriculture and USDA released the Winsome fly from 1998 to 2006, with the majority being released at Theodore Wirth Park in Minneapolis. The Winsome fly is considered one of the more effective biological control agents for Japanese beetles. Although parasitism rates have been historically low in Minnesota, recent research in 2024 indicate that the Winsome fly is adapting to Minnesota’s climate, including warmer winters, and the fly’s emergence is better aligned with that of the Japanese beetle’s emergence. The Winsome fly appears to be a very promising natural biological control for those Japanese beetles that do so much damage to our crops and ornamental plants!
Dear Master Gardener: I planted bee balm this spring and I noticed it has white powder all over it. How do I get rid of it?
Powdery mildew on a Veronica ornamental plant.
Contributed / Jennifer Knutson
Answer: Powdery mildew is a common fungal disease found on many garden plants. It often attacks plants that are in too much shade or planted too closely together (restricting airflow.) Bee balm is one of many ornamental plants that is prone to powdery mildew. Avoid using a fungicide because it won’t cure it or get rid of it. Although it is unsightly, powdery mildew does not significantly damage the plant. In the future if you add more bee balm to your gardens, or want to replace what you have, the varieties/cultivars that are resistant to powdery mildew include: Monarda fistulosa (wild bergamot), Raspberry Wine, Marshall’s Delight, Jacob Cline, Claire Grace, Bee-You Bee Happy, and Bee Bright.
Dear Master Gardener: My friend gave me Sweet William seeds which I planted in my garden this year in full sun. I have stems and leaves but no flowers. What could be wrong?
Answer: Sweet William (Dianthus barbatus) is a biennial, which requires two years to flower. You won’t see flowers this year, but you will see them next year as long as you planted them in well-drained soil. The first year you plant Sweet William, the plant grows its roots, stems, and leaves. The second year the plant flowers, produces seeds, and then dies. If the plants are happy in their location, they will reseed and you will get plants yearly once they become established. This is a classic cottage garden plant and an excellent cut flower with a long vase life. Sweet William is hardy to zone 3.
Dear Master Gardener: Would wild ginger make a good groundcover for my woodland garden?
Answer: Yes! Wild Canadian ginger (Asarum canadense) is a great choice for a woodland garden. It is a Minnesota native plant found in moist woodlands and forests. It gets about 6-9 inches tall, grows best in part to full shade, and spreads by rhizomes. The leaves are heart-shaped and densely covered in soft hairs on the underside. Canadian ginger flowers in the spring, but you have to look hard to find the flower. Each plant has a single, brownish-red flower that is jug-shaped and lies on the ground at the base of the plant between two leaves. As an aside, it is not related to the ginger we use for Asian cooking.
Dear Master Gardener: I visited a friend in northwestern Minnesota who has an interesting plant called dwarf indigobush. What can you tell me about it?
Answer: Dwarf indigobush (Amorpha nana), also known as fragrant false indigo, is a Minnesota native plant that is definitely worth looking for! It is native to most of the western half of Minnesota and Crow Wing County. In its native habitat it is found in sunny upland prairies. This plant will not only add beauty to your landscape, but is excellent for pollinators. In early summer dense spike clusters of indigo-colored flowers with contrasting yellow stamens cover this deciduous shrub. Small green legume pod fruits persist into winter. This is a very short shrub, growing to a mature height of one to two feet. Dwarf indigobush blooms on old wood, so if you cut it back, it will not flower until the following growing season.
You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, email me at
umnmastergardener@gmail.com
and I will answer you in the column if space allows.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.
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