COLUMN: Fighting the 'green menace'

THE NATURE OF THINGS COLUMN
By: 
Michele Olson
Jones County Naturalist

     This year’s Japanese beetle hatch has begun; Popillia japonica has been silently invading Iowa for the past 45 years.

     In the past 10 years it has multiplied enough in Jones County for almost all residents to take notice. More homeowners and gardeners are asking what can I do to control this “green menace?”

     Accidentally imported into New Jersey from Japan with ornamental plants in 1916, this stout green and bronze beetle has been making its way across the United States with the help of nursery stock plants and landscape sod. Making its first appearance in Iowa in the 1970s, it didn’t gain a good foothold until the late 1990s and is now being noticed in large numbers by residents in over 63 of Iowa’s 99 counties.

     This stout little beetle measures about 1/3 to 3/5 inches long. It is easily identified by its greenish bronze head and thorax and metallic bronze colored wing covers. Prominent white hair tufts along the abdomen are a dead give away. If threatened, the Japanese beetle will stick a set of legs out of the sides of their body in an effort to look more menacing and scare away would-be predators.

     The adult beetles, where present in Iowa, can be found from June through mid-August. They are not picky eaters and have been known to feed on over 350 different kinds of plants including garden vegetables, flowers, fruits, trees and shrubs. When feeding, they eat the leaf tissue but leave the veins intact, leaving a tell-tale skeletonized leaf behind. Some plants they seem to prefer include roses, grapes, raspberries, and linden trees. Once you find one beetle you are unfortunately destined to find more.

     Adult females interrupt feeding on plants to lay eggs in the ground. Larvae hatch and remain underground feeding on grass roots and organic matter until the following June and July, when they emerge as adults searching for plants to eat.

     Beetle control can be difficult. If you are lucky enough to only find a limited number of these little green eating machines in your yard hand removal and Mother Nature’s predatory insects and hungry birds should suffice. Japanese beetles are sluggish in the early morning hours before the sun warms them for rapid flight. They can be easily picked or shaken from plants at this time and placed into a bucket of soapy water for disposal. To protect themselves when their menacing stance fails, they will fall to the ground and burrow under the soil and loose substrate or take to the air by flying to escape predation. In our yard, the brown thrashers love to catch and eat them.

     If you simply want to save select plants, screens and barriers such as cheesecloth can be used to cover prize specimens when beetle activity is at its peak.

     Pheromone-based Japanese beetle traps will attract and kill Japanese beetles where you place them, but will also attract more beetles to your yard. Therefore, use of these traps should be avoided.

     Spot spraying insecticides should be used only as a last resort as they are not target-specific and will kill other insects as well as the Japanese beetles. As always, utmost care must be taken when using chemicals with plants that will provide a food crop. Several insecticides are labeled for use against adult Japanese beetles. Always follow labeled directions. Apply in the afternoon when beetles are most active. Multiple applications will probably be needed. Avoid spraying insecticides when bees are foraging or under windy conditions.

     A homemade alternative spray deterrent can also be made by pouring hot water over cedar planks or cedar tree boughs in a one or two gallon bucket and allowing the cedar plank and boughs to steep, like tea, for 24 hours. The liquid can then be used to spray over plants to deter beetles from eating them. Controlling grubs can be attempted by withholding irrigation of lawns during peak adult beetle flight – creating unfavorable conditions for the eggs and young beetle larvae. Biological control for grubs includes the milky spore disease, insect-parasitic nematodes, and fungal pathogens such as Beauveria bassiana and Metarrhiizium. Insecticides applied in early-mid August can help control grubs in your yard, but are not species specific and will affect other insects and even birds in your lawn. Unfortunately, even if you treat your yard you are still likely to have Japanese beetles next year since beetles are capable of flying in from nearby untreated areas.

     In some instances it is recommended to simply tolerate the unsightly defoliation of plants caused by these little green menaces as you wait for them to complete their lifecycle and disappear for another year.

     If you would like more information on Japanese beetles visit the ISU Extension website at https://hortnews.extension.iastate.edu/japanese-beetle, or contact Michele at 563-487-3541.                

 

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