Japanese Beetles, Milky Spore and Soil Inoculation

Japanese Beetles (Popillia japonica) were first spotted in the US in 1916. It is believed that they were accidentally imported in Japanese iris bulbs and found their way to a nursery in New Jersey. Since that time, these voracious pests have steadily moved south and westward leaving a swath of damage in their wake. The adult beetles damage the leaves of more than 300 different kinds of plants, while their larvae love the roots of turf grasses, vegetables and ornamental plants as they move up through the soil and pupate into adulthood.

One of the great (and scary) things in nature is that every living thing on the planet has a natural enemy – or two. Even more amazing is that many natural enemies are specific to their targeted prey. In the world of bio-rational controls, this is especially remarkable. One of the great benefits of bio-rational controls in the garden or crop is that they target one family or species of pest and leave all the others – particularly the beneficial insects – alone.

Milky Spore (Paenibacillus popilliae, formerly Bacillus popilliae) falls into the category of bio-rational controls because of its target specificity. While there is no evidence that it will help to control other white, C-shaped grubs, it is a powerhouse treatment for control of the grub (larval stage) of the Japanese beetle. Milky Spore ticks all the safety boxes – it will not harm humans or other mammals, reptiles, aquatic life, or plant material. Click here for more information on the main ingredient in Milky Spore.

Milky Spore Can Inoculate the Soil for Up To 20 Years

Many controls for pest insects require repeated applications with no end to it in sight. Milky Spore, however, has the added benefit of inoculating the soil after several applications. What this means is that the soil will carry enough of the bacillus that any grubs that hatch in the area will not survive.  Depending upon your climate, fully inoculating the soil can take between 1 and 5 years.

• In warm climates inoculation requires 1 – 3 annual applications.
• In colder climates inoculation requires 3 – 5 annual applications.

Milky Spore begins working as soon as applied so long as grubs are feeding. This means spring and autumn applications of Milky Spore are most effective because the grubs are most active at that time. Don’t forget that beneficial nematodes are great for seasonal control of the Japanese Beetle. They are effective on a broad range of in-soil pest insects and they will help to more effectively distribute the powder form of Milky Spore.

The cause of death from P. popilliae is not fully understood. The most likely cause is from starvation as the bacterial cells grow in the grub’s hemolymph - the blood-like fluid in invertebrates. The already milky looking grubs become even milkier looking and fail to mature.

Damage from Japanese Beetles

Milky Spore is available in powder and a new granular formulation. The granular product is applied using a hand spreader or a drop spreader. The powder formulation can be applied with a dispenser tube or for small areas, by the teaspoonful spaced in a checkerboard pattern every 4 feet. 

Community use of Milky Spore will help to most effectively reduce the population of the Japanese beetle in your area. Remember, the adult beetles are not affected by the Milky Spore and by their nature are highly mobile – they will be moving into your area throughout the summer months. The more of your neighbors who inoculate their soil, the better the control will be. 

Posted by Deb N.

Japanese Beetle Control 101

Japanese Beetles can decimate crops above and below ground, leaving huge swaths of land barren and unproductive. These grubs are naturally detritivores (meaning that they eat decomposing materials), but they also feed on plant roots. Once they start to feed on roots, water and nutrient uptake is severely hindered. This results in brown and patchy dead spots in turf, lack of plant vigor and stunted growth. Unfortunately for the grower, this is only part of the plague that is the Japanese Beetle. 

Adult Japanese Beetles skeletonize leaves, strip flower petals and damage developing fruit. While their grubs feast on plant roots, the adults are opportunistic and tend to eat whatever they can get their little (yet voracious) mouth parts on. Some of their favorite host plants include roses, beans, grapes and berries.

Where Are They? Should You Be Worried?

Japanese beetles are found predominately in the eastern part of Unites States, from the Atlantic coast to states that border the west side of the Mississippi river. They have, additionally, been spotted in several Midwestern states, although their numbers and distribution vary in these regions (i.e. Texas is only considered partially infested). Chances are if you live in an area with lawns, prairies or grazing areas, you can expect Japanese beetles to make their way to you, if they haven’t already. 

What Do They Look Like?

Japanese Beetles are often described as iridescent green beetles. Other beetles like the Fig Beetle and False Japanese Beetle are often mistaken because of this. While their heads are a metallic green, their wings are a brown to bronze color with recognizable white tufts around them. Look for the tufts for a positive ID!

How Do We Control Them?

The best way to control Japanese Beetles is by stopping them before there is an infestation through preventative treatments. These treatments include applying beneficial nematodes to kill grubs, using Milky Spore to prevent yearly recurrences and utilizing row covers to limit damage. 

If prevention is not an option or if you have adult beetles making their way in from nearby areas, then direct, spray-on treatments will be your best plan of action. The infective fungus, Beauveria bassiana, kills both grubs and adults while remaining harmless to beneficial insects. It is a fantastic choice for organic growers trying to stay away from conventional pesticides. Surround WP is the next best option to save your plants from damage. Sprayed onto foliage and fruit, it deters beetle feeding and helps shield plants from heat stress.

There are a number of DIY traps we have found online and would love to hear any other ways you have found to control these bad hombres!