There’s been a lot of hubbub and even panic about the Japanese Beetles that are now swarming the Omaha metro area. Having just moved from West Virginia, where the beetles are endemic and a commonplace pest every year, I had to ask what all the fuss was about here in Nebraska. I was then schooled that they are relatively new here, and have been appearing en masse this year. Having experience with this pest, I’ll tell you that the population will generally explode for the first few years, then level off to a more manageable level. We’ll hope I’m right about that.
These destructive pests can decimate a landscape, but they can also do some serious damage to vegetables and fruits. Adult beetles will feed on just about anything if they are hungry enough, but they definitely have their favorites. Most commonly, they feed on fruits such as apple, crabapple, grapes, peach, cherry, blackberries, and raspberries and vegetables such as asparagus, corn (foliage and silks), beans, okra, and rhubarb. Our hops specialist has also reported damage on hops. Grubs will feed on the roots of many vegetable transplants in the garden, but favor roots of corn, beet, beans, asparagus, tomato and onion.
The damage can be significant. I recently spoke with a local farmer who grows raspberries who, despite using every means possible for an organic grower, cannot get enough control of the beetles to save his crop. He’s so frustrated that he asked if it is even still economically viable to grow raspberries in the future. My advice: stay the course for the next few years to see if populations decrease to a manageable level.
Controlling Japanese Beetles on Vegetables and Fruits
When controlling pests on fruits and vegetables, there are a few more considerations you have to make than dealing with them on ornamental plants. The big difference is food safety by following the label directions for what can be used on food plants, and how soon you can harvest after the last application. This means that controls are a little more limited than in ornamentals. Keep in mind that many pesticides, even organic ones, can pose a risk to bees and other pollinators. Many labels now contain a “bee box” with information on how to reduce risk to pollinators, such as applying after dusk when bees are no longer foraging.
Cultural controls are ideal for small vegetable gardens or fruit plantings, but since many of them are labor intensive, they may not be practical for very large gardens or farms. Probably the most common form of cultural control is by picking the beetles off of plants by hand and dropping them in a bucket of soapy water to drown. This process will need to be repeated often (daily) while the Japanese beetles are present. Another method for lower-growing crops is to use a floating row cover or mesh-like material to cover crops before the beetles emerge. Creating a barrier between the plants and the beetles is a good control method, but if it is a crop that requires bee pollination the covers will have to be removed if the plant is in flower.
Many people buy the traps for Japanese Beetles that you find at the local garden center. Every expert agrees: DO NOT BUY THESE TRAPS. They end up attracting more, many more beetles, than they actually capture. Plus, the extra beetles that are attracted release more of the attractive odors (it is a sex pheromone) that attract even more beetles.
And the unfortunate thing is that we provide prime real estate for the female Japanese Beetle to lay her eggs and for the young grubs to feed – their preferred food is grass, especially that which is kept well irrigated. While you can’t really go around ripping up all the grass in the neighborhood, nor will ripping up all your grass keep the adults from flying into your garden. But if you have grass as a living mulch in your vegetable garden or around your fruit plants, eliminating it can help reduce the possibility of damage to the roots from feeding grubs on susceptible plants.
There are some control options available for those who are either certified organic farmers or who wish to keep their home gardens organic. The major drawbacks to these products versus conventional pesticides is that they are less effective at control and have a shorter residual effect. They can be useful for mild infestations, but may not control heavy infestations of Japanese Beetle.
Pyrethrum is a common organic broad-spectrum insecticide that can be used to control Japanese Beetle. The chemical is extracted from a member of the chrysanthemum flower and is available in a number of brands and formulations. Many of the main pesticide companies have a pyrethrum product on the shelf, though one of the more common ones used is Pyganic.
Neem oil, an extract from the Neem tree seed, is another organic control. It is also a common find on most store shelves. Some products are also available that have an isolated/concentrated form of the active ingredient azadirachtin. It is available under such names as AZA-Driect and AZA-Guard, but are likely harder to find than the straight neem oil.
Another more recent organic pesticide that may hold promise for controlling Japanese beetle is Spinosad. It is composed of compounds extracted from a bacteria.
Another option is to use a product called SURROUND. It kaolin clay suspended in liquid that is sprayed on to the foliage or fruit of the plants. It both alters the appearance of the plant to the beetles and reduces access for feeding. It does have to be reapplied after rain and may be difficult to wash off some fruits.
There are some natural enemy controls aimed at reducing numbers of grubs in the soil. These can help reduce damage to roots from grub feeding, but likely won’t reduce damage from feeding adults since they can fly from a distance to get to your garden. Nematodes that prey on grubs are available commercially to treat lawns and other areas where grubs are found. A bacteria, called milky spore disease, is also commercially available, but recent studies show it isn’t as effective at control as originally claimed and may have to be applied multiple times over multiple years for control.
The most effective and most economical control is carbaryl, most commonly sold and known as Sevin. This chemical is highly effective against Japanese Beetle. However, it also poses significant risk to bees. Follow label suggestions for mitigating risk, and be sure to use it in liquid form rather than powder form, as the powder form can be picked up and carried back to nests or hives by bees.
Other conventional controls include malathion, permethrin, cyfluthrin, and diazinon. Always consult the label of these products to make sure that they can be applied to the fruit or vegetable crop you are treating, as they may not be useable on every crop. And also check the label for the pre-harvest interval, meaning how long you have to wait from last application of the pesticide to harvest. It can be as little as a few hours or as long as weeks.
For assistance in developing a control plan, contact our office (if you live in Douglas or Sarpy Counties, NE) or your local extension office.
Photo: Jody Green, UNL Extension