One insect, 300 target plants. That’s the reality when dealing with Japanese beetles (JP), especially in boom years, like the one predicted in 2017.
This half-inch beetle with a voracious appetite prefers rose plants and linden trees but has been observed defoliating over 300 different types of plant and tree species. It’s not just the actual adult beetle which hurts. JP destroys gardens and lawns throughout its lifecycle. While in its larval stage, more commonly known as grubs, they feast on lawn roots, creating brown and yellow patches of grass which at their worst can be lifted up like pieces of carpeting.
Warming Front Range soils are waking up insects of all sorts – but none is freaking out gardeners more than JP. This year is predicted to be an up year in the cycle, due to the especially wet year we’ve experienced -which creates a more ideal breeding ground for the JP to lay eggs. Short of a long dry end to the growing season, which would destroy the drought-phobic JP in large numbers, get ready for lots of stripped leaves this year and next year.
It’s not just the actual adult beetle which hurts. JP destroys gardens and lawns throughout its lifecycle. While in its larval stage, more commonly known as grubs, they feast on lawn roots, creating brown and yellow patches of grass which at their worst can be lifted up like pieces of carpeting.
Basic Japanese beetle facts:
Japanese beetles are an invasive species that are now deeply embedded in the ecology of Colorado. Interestingly, the beetles are not considered a pest in their place of origin, Japan. The beetles were accidentally released in New Jersey in 1916. They were first found in Colorado about 60 years ago [see Japanese beetles in Highlands Ranch ].
JPs begin as grubs where they chew and damage the root structure of lawns. Besides lawn roots, they also are recorded feeding on the roots of beans, strawberries, and tomatoes. The females begin to emerge in June and July and are observed feeding on vines, linden trees, roses, and over 300 other ornamental plants. Adults live for about two months.
The reason Japanese beetles are such prolific breeders is that they naturally attract more beetles to a given plant as they chew the leaf structure and give off a natural pheromone that invites other adults into the fray.
Wetter years may promote the adult emergence weeks earlier than normal, and all the late-spring snow we’ve had in Denver seems to be doing just that. If you’re observing more than a few beetles on your trees and shrubs, it’s important to act as soon as possible.
We offer professional treatment if home remedies stop working – and when JP beetles swarm, they can overwhelm even the most dedicated gardeners.
The best time to attack JP is during their egg stage and hatch in later summer and early fall. Applying a granular insecticide with a spreader to the lawn at this time offers the strongest chance of control. Control will be improved by a moderate to light watering by hose or normal sprinkler system schedule. However, significant rainfall after the application may be counterproductive and require a second round.