Saturday, August 12, 2017 1:00 am
Japanese beetles are back
Question: I am seeing damage on my cannas, roses and other plants this summer. There are many metallic-black/brown beetles on the plants. What are they, and how do I get rid of them?
Answer: It appears as if Japanese beetles have made a bit of a comeback in this area this year. Many folks forget that 20 years ago there were tons of Japanese beetles ravaging plants in our area. The populations diminished over time as the beetles moved west. Maybe they miss Indiana.
Right now, the adult beetles are on the prowl eating the foliage of their favorite plants. These beetles emerged from the ground in July after overwintering. The first emerging adults are females which release food and attractant pheromones for the male beetles that emerge later. The beetles mate and then the females lay eggs in the ground (usually the lawn) which hatch in August or September. The C-shaped larvae are white with a brown head. They feed voraciously on the roots of turf grass and can cause considerable damage to the lawn. If untreated, the larvae overwinter in the ground and then pupate and change into adults which emerge the following year.
Japanese beetle adults can be controlled with several methods. It is important to protect pollinators such as bees when trying to control Japanese beetle adults. Try to avoid applying pesticides directly on flowers, and try not to use systemic insecticides (ones that travel within the plant sap) on flowering plants.
One way to control beetles is to mix about one teaspoon of dish soap into a gallon of water. In the early morning or late afternoon when the beetles are sluggish; simply knock off the beetles into the bucket of soapy water. Pour out the dead beetles for the birds to eat.
Neem is an organic pesticide that not only kills the beetles on contact, but also will repel them away from desirable plants. There are many other conventional pesticides that will control beetles. Always read the label of the product to make sure you apply it correctly and safely.
Under no circumstances should one ever use a Japanese beetle trap. They are sometimes sold at garden centers and online. Unfortunately, the traps will only draw more beetles into the area – more beetles than even the traps can handle.
If you notice many adults in your garden and landscape this summer, be on the lookout for lawn damage later on. The damage usually appears in August and September with browning areas. The lawn will lift up like a carpet revealing the grubs below. Rescue treatments such as Dylox can be used to control the grubs.
Milky spore is touted as an organic control for lawn grubs but the results are mixed at best. Better to control the adults so lawn damage doesn't occur later in the year.
The Plant Medic, written by Ricky Kemery, appears every other Saturday. Kemery retired as the extension educator for horticulture at the Allen County branch of the Purdue Extension Service.