Gardening Sweet Spots
By Donna Hessel
It’s that time of year – one day your zinnia flowers are colorful and ruffled. The next day, only ragged edges and holey leaves remain. What happened overnight? Japanese beetle attack!
You may notice Japanese beetles on your zinnias and on other plants, too. They love roses, dahlias, hollyhocks and hibiscus. You may also see them on Japanese maples, sunflowers, clematis vines and other ornamentals. The best time to catch them is early morning when they’re still sluggish and less alert from cool night temperatures. You can pluck or shake the beetles from plants into warm soapy water for a quick kill. Or you can squish them if you’re less squeamish than I am about that sort of thing.
If you are fortunate enough to live in an area where there are only a few of these pests, hand picking will eliminate them. However, if you are overwhelmed with a colony of them, you may want to use a commercial product to control them. A multipronged approach is your best bet. Start by spraying the affected plants with a pyrethrin-based insecticide or neem oil. Pyrethrin is safe and effective. Neem oil is derived from a tree and reduces the feeding by the beetles. It works best if applications are started at the first sign of attack. If subsequent defense is called for, you may have to resort to systemic or surface insecticides. Systemic insecticides, such as those containing imidacloprid or thiamethoxam, are absorbed into the plant, giving them long-term protection. Contact insecticides like carbaryl, sold as Sevin, can be applied as a spray or a dust. They only stick to the surface of the flower and need to be applied often.
So why not mount a Japanese beetle trap to attract and trap the beasts and keep them away from your flowers? The traps are baited with floral scents and sex pheromones that attract the beetles. The bait is so attractive, however, that it may bring beetles in from as far away as 1000 ft. A trap could exacerbate the problem! If you do decide to use one, put it far away from anything you don’t want the beetles to eat.
The appearance of Japanese beetles is not incidental. They have been in your yard for at least a year prior to their emergence in summer as beetles. Much of a beetle’s life cycle takes place underground. Life starts as an egg laid by a mature female Japanese beetle who mates, lays one to five eggs two to four inches underground, then returns to eat more of your flowers and continue the mating process until 40-60 eggs have been laid.
Eggs hatch in 8 to 14 days and the small grubs feed on roots and other organic materials. The grubs are as destructive to turf roots underground as the adults are to your flowers and foliage in the summer. If you have skunks visit your yard as I do, you will find holes in your grass where they have dug up grubs to eat. I consider them a “natural control” and just stomp the grass tufts back down.
As the grubs grow, they shed their skin several times. If you pull back a patch of sod in late summer and find grubs, it’s a good time to apply a grub control product. Late spring to early fall are the best times good time to apply pesticides. Look for either a spray or a granular material that contains imidacloprid or halofenozide. Milky spore is an organic grub control. It’s a bacteria that is mixed with water and sprinkled on the lawn. It may or may not be effective in your area. It can be purchased from garden nursery catalogs or some garden centers.
As autumn temperatures drop, the one-inch-long, fat grubs burrow 6 to 18 inches into the soil to spend the winter. After wintering deep in the soil, grubs hatched the previous summer rise to the surface in late spring to feed on roots. In late spring, the grub forms a pupa one to three inches deep in the soil. In a few weeks, the adult hatches and crawls to the surface as the mature Japanese beetle to challenge you, eat your flowers and repeat the procreative process.
If Japanese beetles are a major problem in your area, you may want to take some offensive action and plant things beetles don’t like. If there are more plants they don’t like than those they do, they may ignore your garden all together. Beetles don’t like coral bells (Heuchera), coreopsis, delphinium, foxglove, hostas, impatiens, lantana and nasturtium. Some of these, however, the deer find tasty. Some are better for sunny gardens and others for shady gardens. So you’ll need to do your research. (And keep a jar of soapy water on hand.)
Reference: Garden Gate Newsletter, July 2018.
Photo courtesy pexels.com
