Tag Archives: Japanese Beetles

Japanese Beetles Make Their 2018 Debut

 

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The Japanese Beetle – pretty to look at but oh so destructive!

June is a glorious month in the garden, but it also the cue for adult Japanese beetles (Popillia japonica) to emerge from the soil. They’ll hit their peak from late June through at least August. I haven’t spotted the metallic green and copper devils in my garden yet, but if the past is any indication, they’ll visit soon.

Colorado State University offers this comprehensive fact sheet with everything we need to know to defend our plants. It’s an especially valuable reference when considering products which may or may not be beneficial in reducing the pests while doing minimal damage to the ecosystem. If there were best seller lists for gardener information, this would be on the top!

Here are important takeaways from the fact sheet:

05601-fig5Japanese beetles feast on foliage, buds and flowers of their favorite plants. Particularly susceptible are roses, Virginia creeper, Linden trees, Rose of Sharon, Japanese maples, Silver lace vine and Gaura are among their favorite targets. Tell-tale signs of Japanese beetle damage are a skeletonized pattern of mutilation on tender, new foliage and deformed flowers or buds. While unsightly, the damage will not kill the plant.

05601-fig8Traps are not beneficial. That yellow trap you’re tempted to hang in your yard is an open invitation for more Japanese beetles to visit. The trap won’t be able to catch them all and the effect is more, not less damage. Perhaps if your neighbor hangs one…?

Picking does help. Japanese beetles are easy to spot in the cooler parts of the day and can be coaxed into a jar of soapy water with a twig or a shake. Catching is preferable to squishing, as a squashed beetle releases a compound which lures more of their kind. While it may not be fun, catching is oddly satisfying!

Do insecticides work? As always, caution must be used to avoid damage to pollinators, especially when plants are in flower. Products containing pyrethrins, azadirachtin and acetamiprid – used in the early morning or at dusk – when bees and other pollinators are less active – are the safest. See the fact sheet for more details and follow all product recommendations carefully.

Consider removing temptation. Can you replace your Virginia creeper with something less enticing? Do you have roses that have struggled for years? Perhaps it’s time to replace with something less alluring. Conversely, when adding to your landscape avoid plants which are irresistible to this insect.

Late season turf damage. Each female Japanese beetle lays 40-60 eggs in her 4-8 week life span. Eggs are laid deep in moist turf soil. Since eggs and subsequent larvae thrive on moisture, keeping soil on the dry side will inhibit grub development and decrease turf damage. Grubs also munch on turf roots, so mowing at a higher height, which promotes vigorous roots, can help reduce turf damage.  More control ideas can be found in this fact sheet.

Have you spotted Japanese beetles in your garden yet?

 

Submitted by Linda McDonnell, a Denver County Master Gardener

 

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Do Japanese Beetles Prefer Some Roses More than Others?

Colorado roses have been attacked by Japanese beetles for several years, leaving behind ravaged foliage and deformed flowers. Curiously though, some gardeners report that their roses suffer little to no damage from the insect. Are some rose cultivars less enticing to the Japanese beetle than others? This was the focus of Colorado State University’s 2016 observational study conducted at Littleton’s War Memorial Rose Garden. In the first year of this multi-year study, the following rose cultivars were not found to be damaged by Japanese Beetles: Angel Face, Debut, Hondo, Joseph’s Coat, Mardi Gras, Picotee, Popcorn, Prima Donna, Ralph Moore, Singin’ in the Rain and White Lightnin’.

Conversely, the following cultivars were observed to have the highest levels of Japanese beetle destruction: Pink Promise, Honey Perfume Whisper, Love and Peace, Day Breaker, Strike it Rich, Cherry Parfait, Eureka, Starry Night, Rainbow Knock Out, Lady Elsie May, Carefree Delight and June Lover.

Adult Japanese beetles destroy flowers at the same time bees are gathering pollen, making their impact even more significant. For this reason, CSU’s study identified roses with high Japanese beetle susceptibility and high visitation by bees. Topping this list were Rainbow Knock Out, Lady Elsie May and Strike it Rich. Also in this group were Prominent, Home Run, Easy Does It, Apricot Nectar, Gemini, Starry Night, Baby Boomer, Sweet Diana, Julia Child, Cathedral, Betty Boop, Mon Cherie and Cloud Dancer.

Early findings suggest that gardeners may be able to lessen damage to roses by planting cultivars that are less attractive to Japanese beetles. It also underscores the importance of close monitoring and care of plants to reduce the effects on pollination. In the future, additional information on why some cultivars are preferred over others is likely to emerge.

This CSU publication provides comprehensive information on caring for plants infested with Japanese beetles, the larvae stage effecting turf and more. An additional bit of advice – it has recently been found that crushing the Japanese beetle does not attract more beetles. So, while we’ve previously been advised to handpick and drown the insect in soapy water, feel free to stomp on them too. Since they are night feeders, they are easiest to find around dusk, when they are about to feast on your plants.

Written by Linda McDonnell, a Denver County Master Gardener

Note: The study cited in this post was presented to the Denver County Master Gardener Association by Dr. Whitney Cranshaw of Colorado State University in May 2017.

Photos courtesy of http://www.pixabay.com