Knowledgebase

What is eating my hibiscus and what can I do about it? #772572

Asked September 21, 2021, 3:58 PM EDT

Something is eating holes in the leaves on my hibiscus. I've been told it may be from Japanese beetles. Whatever the cause, what can I do about it?

Lapeer County Michigan

Expert Response

This does appear to be damage caused by Japanese beetles. You should have seen them on your plant earlier in the growing season. They have pretty much finished their adult stage for this year.

Adults emerge from the ground between late June and the middle of August. In a normal year, most of the adults emerge in July.  The peak of their chewing activity lasts from late June through August when they will begin to die off due to temperature and climate. So there's not much you can do to control the beetles this year. But next summer you can apply an insecticide between July 1 and 15 to control the grubs. (More information below.)

The adult females have been busy laying eggs which will become larva, or C-shaped white grubs. The grubs feed underground mostly on the roots of grasses until mature and become adults (beetles).

We do not recommend using traps to catch the adults. Traps tend to attract Japanese beetle adults from a large area (your adjacent properties) thereby increasing their population in your lawn or garden.  Although the traps are often sold as a control measure, it is not likely that trapping will reduce the population, and may increase it.

The best way to control these critters is to target the grubs. Preventive insecticides with the active ingredients imidacloprid,
thiamethoxam or clothianidin should be applied to your lawn between July 1 and July 15 for optimum control. Mow the turf to be treated prior to application to make sure there are no open flowers attractive to bees. Another active ingredient, chlorantraniliprole, is also an effective preventive
treatment, but should be applied between May 1 and July 1 to be most effective. Preventive compounds do not work well after Aug. 15.

Controlling the adults which chew on your leaves can be difficult. Because the beetles are poor flyers,the safest and easiest way (unless you're squeamish) to eliminate them is to use a gloved hand and swipe them off the leaves of your plants into a bucket of soapy water.

If you choose to use an insecticide to control the adults, sprayable products containing the active ingredients carbaryl,
bifenthrin, cyfluthrin, lambda-cyhalothrin or permethrin are the best choices for adult control. If the population is high, insecticide applications may need to be made on susceptible plants every four to seven days while adults are active.
When the leaves of susceptible plants are damaged, they give off
chemicals that seem to be a dinner bell for other adults to join in the meal.

Although most insecticides for Japanese beetle control can be purchased over the counter, remember that they are poisons and must be used carefully and according to the label. Always wear long pants, a long-sleeved shirt, rubber boots and rubber gloves when applying insecticides. Keep the wind to your back when applying insecticides. Be careful when mixing insecticides. Wear rubber gloves and do not spill any of the insecticide solution on your skin and clothes. If this happens, wash immediately with soap and water.

While Japanese beetles are probably here to stay, there are some years when the populations are much lower or higher than the previous year.




An Ask Extension Expert Replied September 22, 2021, 3:25 PM EDT

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