Thursday, September 27, 2018

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.

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