These cranberries are for the birds

Standing on the path at the Clergy House on Water Street, you will notice a couple of beautiful native shrubs: Highbush Cranberry (Viburnum trilobum) and Silky Dogwood (Cornus amomum). You will undoubtedly also notice the highly invasive Japanese Beetle (Popillia japonica), busily feeding on the leaves of these shrubs.

Even though the berries of a Highbush Cranberry look like cranberries and are tolerably edible, they are very different from the bog cranberries we love to feast on at Thanksgiving. With showy white flowers in spring and berries in the fall and winter, these highbush shrubs are native in every province in Canada and are a “must have” for even the smallest property. They will tolerate partial shade but will flower and fruit more readily the more sun that is provided. They like moist soil but will adapt to drier conditions. Other Viburnum species native to our region include Nannyberry (Viburnum lentago) and Hobblebush (Viburnum lantanoides) whose berries provide food for the birds and are some of those important understory plants.

A favourite native vine for birds and pollinators, Virginia Creeper (Parthenocissus quinquefolia) is also found at this location on our walking tour. An aggressive plant in Southern Ontario, Virginia Creeper is a welcome addition to our native landscapes, useful as a climbing vine and as ground cover particularly in those hard to cover shady areas. How can we distinguish it from Poison Ivy (Toxicodendron radicans), an uncommon native in our region? Learn this little ditty and you’ll never be left wondering again: “Leaves of three, let it be. Leaves of five, let it thrive” (but never eat the berries – they’re toxic to humans). Virginia Creeper will attract pollinators to its flowers in spring and many birds to its berries in fall and winter. It’s also a host plant for the larval form of many moths.

If you happen to be on the Riverwalk during July and August you’re going to see groups of metallic green and copper coloured beetles. They’re pretty big, about ½” (10mm) large. They emerge from the soil and fly from rose bush to highbush cranberry bush skeletonizing the leaves and leaving not so much as a crumb for the beleaguered local native insects. They aren’t fussy eaters and will consume over 300 species of plants although they prefer fruit trees and fruit bearing shrubs.

As a gardener what can you do at home to stop this infestation?

There's not a lot you can do to halt the Japanese beetle since it has few native predators but understanding their life cycle will help to implement the right strategies at the right time.

Daily hand pickling has been proven to be effective at reducing populations on small properties and a study has shown that the ideal time is at 7 pm. It likes to eat during the day and is particularly active in hot sunny weather. You can’t miss its large size and flashy colour and you should be able to easily flick it into a bucket of soapy water.

Stop watering your lawn and shrubs during the month of August to let the soil dry out. The dry conditions will cause the eggs of the next generation to wither and die. The larval form of the beetle is the same white grub that is found consuming grass roots in lawns.

Reduce or eliminate your lawn/turf areas. Japanese beetles don’t like tall grass, so let your lawn grow to 8 cm during July and August at the height of egg laying season.

Learn to make friends with parasitic wasps as they lay their eggs in the bodies of beetle larvae causing the larvae to die.

Mulching under shrubs with wood chips can reduce the larval form of the beetle and consequent damage to roots.

Japanese Beetle traps are commercially available but OMAFRA writes that most authorities on the topic discourage their use. Their reasoning is that the traps effectively attract beetles from far and wide, too many to be caught by the traps and you end up with more plant damage and more adults laying eggs in the soil around the traps. For more information consult the OMAFRA

U-Links Species Profile:

Japanese beetle, Popillia japonica

Native to the island of Japan, the Japanese beetle has been a pest species in Canada, United States, Portugal and Korea for many years (Government of Canada, 2017). This coleoptera (beetle family) was accidentally introduced to North America in 1916, when it was detected in New Jersey during a routine inspection of commercial goods (Potter & Held, 2002). It was then later discovered in Canada around 1939, with its first known location being in Nova Scotia (Government of Canada, 2017). From there, the insect has spread all across Eastern Canada and can now be found across Ontario and will be a populus species along the River walk.

This species is a versatile generalist species when regarding feeding behaviours and host plants. Although they do prefer fruit trees and shrubs which also bear fruit, the Japanese Beetle can select over 300 species of plants to feed upon (Potter & Held, 2002), making this insect a very competitive species against many native species. Both Larval stage and Adult stage feed on the plants, with the larvae starting their destructive eating habits underground, feasting on the rhizomes of the plants they are under (Potter & Held, 2002). Once they grow from their larval grub phase, they transition into the iridescent green-brown beetle commonly seen on the plant leaves. The japanese beetle will eat the fruits, leaves and flowers of the host plant, leaving skeletal-like remains, before flying to the next host plant. These insects are mobile, and can jump from plant to plant with their flight ability (Potter and Held, 2002) creating a difficult task in species removal.

Due to the destructive nature of this insect, it is common to find commercially available traps around common feeding/nesting grounds of the Japanese Beetle. As a result of trap placement it is common for by-catch of other species, especially pollinators, to occur. According to a study conducted by Sipolski et al., (2019) it is possible to avoid catching our natural pollinators and native insects by selecting the correct luring component and coloured trap. The best combination was found to be using all green traps and the floral lure combination of 7 parts Eugenol and 3 parts phenethyl propionate [PEP] (Sipolski et al., 2019). Finding that exact concentration may prove difficult, however there are common insect traps with these components listed in the ingredients list that can be found in local hardware stores.

Researcher: Caleb Brown, Trent University