Master gardeners: Japanese beetles mostly killed off over winter

The University of Illinois Extension offers two comprehensive resources for homeowners when questions arise about roses and the care they require during any season of the year. “Our Rose Garden” is found on the extension’s horticulture website and also was recently made into an App for smartphones.

“These are great resources for those who are interested in adding roses to their landscape design and want to know where to begin,” says Sarah Navrotski, program coordinator for the master gardener volunteers in the DuPage Extension office. “Anyone who already grows roses will find helpful information about pruning, fertilizing, watering and providing winter protection. There are also sections on insects and diseases that can impact roses.”

The “Our Rose Garden” website is urbanext.illinois.edu/roses/. To download the App, visit web.extension.illinois.edu/state/apps.cfm.

Roses are a favorite plant of Japanese beetles. In the June 16, edition of the “Home, Yard & Garden Pest Newsletter” from the University of Illinois Extension, Phil Nixon, educator in entomology, reports that the Japanese beetle numbers should be low this year.

“Many Japanese beetle larvae (grubs) did not survive the winter, particularly in the northern half of the state,” Nixon said. “Research has shown that Japanese beetle grubs do not migrate deeper than 11 inches into the soil for the winter. They die if the soil temperature reaches 15 degrees or if they are subjected to freezing temperatures for two months. Last winter the soil was frozen to … 30 inches deep in northern Illinois for several weeks. Based on previous experience, it is likely that about two-thirds of the larvae died during the winter in the northern half of the state.”

He said rain was a factor, too.

“In addition to cold temperature mortality, Japanese beetle larvae require approximately 11 inches of water from egg hatch in late July into the fall,” he said. “Although we received abundant rain in spring of 2013, much less rain fell from July through October, averaging 9.5 inches during that time in most of the state. Although that was made up in irrigated turf, many grubs probably died in other areas. This will … cause even further reductions in the northern half of the state.”

Japanese beetle traps are generally not recommended. Research shows that the pheromone bait attracts more beetles to your yard than actually end up in the trap and so more opportunity for damage to your plants.

Email your home garden and lawn questions to uiemg-dupage@illinois.edu or call the Master Gardener Helpline at 630-955-1123. Visit our website at web.extension.illinois.edu/dkk/.

Julie Moore has been a master gardener volunteer with the University of Illinois Extension in DuPage County for 10 years and has a degree in ornamental horticulture from the University of Illinois.

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