Denver Rose Society
What’s a rose lover to do? Japanese Beetles invaded the Denver area in 2006 and have exploded in numbers ever since. While some home gardeners are ripping out their rose beds, Colorado State University’s Dr. Whitney Cranshaw had a much better plan. Dr. Cranshaw, a Professor of Entomology, undertook a two-year study to determine the cultivars to use in our post-Japanese Beetle landscape.
With more than 200 cultivars, the War Memorial Rose Garden in Littleton provided Dr. Cranshaw and his team a unique opportunity to study both Japanese Beetle Damage and visitation by pollinating bees. Damage by the beetles was evaluated on a sliding three-point scale. There was wide variation in the levels of beetle damage, but the rose classes which sustained the least damage were Hybrid Teas, Landscape Shrubs, and Grandifloras. The greatest incidence of Japanese Beetle damage occurred on Shrub roses.
About eleven percent of the cultivars had both high Japanese Beetle damage and high visitation by pollinators, including honey bees, bumble bees and solitary bees. Planting for pollinators is typically desirable, but Dr. Cranshaw notes that this group of roses, which is highly visited by both the beetles and bees, presents the most challenges for management as the need for controls are the greatest but the pesticide options are limited. These roses are the least sustainable, and Dr. Cranshaw recommends against further plantings.
Cultivars with Both High Japanese Beetle Damage and High Bee Visitation
Not Recommended for Planting (Due to Restricted Insecticide Options)
‘Easy Does It’
‘Touch of Class’
‘Climbing New Dawn’
‘Fourth of July’
‘Lady Elsie May’
The great news of the study was that eighteen cultivars had little to no damage by Japanese Beetles and are thus recommended as being sustainable in the landscape.
Recommended for Planting: Cultivars with Little to No Damage from Japanese Beetles
NAME, TYPE (As defined in study), COLOR, FRAGRANCE
‘Angel Face’, Floribunda, Mauve Purple blend, Strong
‘Carrot Top’, Miniature, Orange blend, Mild
‘Child’s Play’, Miniature, White with pink edge, None to mild
‘Class Act’, Floribunda, White, None to mild
‘Colossus’, Hybrid Tea, Deep Yellow, Strong
‘Cupcake’, Miniature, Pink, Mild
‘Electron’, Hybrid Tea, Cherry Pink, Mild to strong
‘French Lace’, Floribunda, White w/ Pink undertones, Mild
‘Gemini’, Hybrid Tea, Pink blend, Mild
‘Jean Kenneally’, Miniature, Apricot blend, Mild
‘Joseph’s Coat', Climber, Red blend, Moderate
‘Kordes’ Perfecta’, Hybrid Tea, Pink blend, Strong
‘Merlot’, Miniature, Red w/ White reverse, Mild
‘Old Glory’, Miniature, Pink, Strong
‘Picotee’, Miniature, Red/white blend, Mild
‘Rainbow Sorbet’, Floribunda, Deep pink w/ yellow edge, None to mild
‘Shining Hour’, Grandiflora, Deep Yellow, Moderate
‘Sun Sprinkles’, Miniature, Deep Yellow, Mild
If endless summers of hand-picking Japanese Beetles off your roses seems daunting, there is now hope. Instead, you can spend your summers enjoying Cupcakes and Rainbow Sorbet, with Merlot by your side. Thanks, Dr. Cranshaw!