Home and commercial gardeners have long waged the battle against insects harming their gardens. After spending time, money and hard work on their gardens, nothing is more frustrating than to have it destroyed by a variety of insects.
The Japanese beetle (Popillia japonica) is one such insect with an infamous reputation. However, the geranium (Pelargonium zonale) is one plant that is winning the war against this destructive beetle.
The Japanese beetle feeds on over 300 varieties of flowers, fruit and vegetables including corn and soybeans. A female Japanese beetle will lay 40 to 60 eggs during her short life of 30 to 45 days. Adult beetles are tiny in length at 7/16 inch long.
Geraniums are annual plants that produce brightly colored blooms in a variety of colors including pink, magenta and red. Geraniums may be grown indoors or outdoors. Most varieties require full to partial sun, and all are heat-tolerant. As of 2010, over 200 geranium cultivars are available to gardeners.
When a Japanese beetle eats from geranium flowers, it becomes paralyzed for 12 to 18 hours. The temporary paralysis happens within an hour of feeding on the plant. During this temporary paralysis, the beetle is highly susceptible to falling victim to one its predators, although some beetles do survive.
One of the first connections between geraniums and Japanese beetles was made in the 1929. Researcher Charles H. Ballou discovered that beetles feeding on geraniums grown in full sun were more susceptible to paralysis than those feeding on geraniums grown in the shade.
As of 2010, the United States Department of Agriculture (USDA) is funding several studies to help identify the exact extract from the geranium leaf that Japanese beetles are drawn to and why it causes paralysis of the insect. Through these studies, researchers hope to develop a more earth-friendly way of controlling the spread of the Japanese beetle.
According to the USDA, the Japanese beetle has caused over 450 million dollars in damage to the ornamental plant industry on an annual basis. Currently, all gardens in states east of the Mississippi river, except Florida, have experienced damage and loss due to Japanese beetles. If they expand into the western United States, warns the University of Kentucky Extension Service, Japanese beetles pose a potentially devastating threat to California vineyards.
Until a more earth-friendly way of effectively controlling Japanese beetles is found, gardeners have several options for pest control. Garden centers offer a variety of pest-control sprays designed to deter Japanese beetles. Chemical formulations are effective for 3 to 4 weeks. There are plant-based formulas based on neem or pyrethrins in canola oil, but they're effective for only about 3 to 4 days and are washed away by rain. The benefit of these sprays is that they may keep other insects away as well.
Picking the Japaense beetles off by hand is another method of removing them from your garden. Japanese beetle traps are available, but they could potentially draw more beetles to the garden than you'd otherwise find there.
Examples of plants and flowers the Japanese beetles don't like include: boxwood, carnations, coreopsis, daisies, lilacs, snapdragons, magnolias, hemlock, hollies, hydrangeas and poppies. Using these in your garden helps prevent the chance of Japanese beetles becoming your new neighbor.