Having trouble with Japanese beetles eating your plants? These adult animals burrow into the ground in the fall to lay eggs, which eventually become larvae. And anyone who has a lawn knows that these maggots can devastate lawns and gardens. An organic control developed to combat the Japanese beetle problem is called milky spore powder.
Japanese beetles (especially adult beetles) take little time to eat grass roots and actively feed on whatever they can in their time above the ground. Then they dig, lay eggs and their offspring (maggots) eventually feed below.
Milky Spore is specially formulated to fight these harmful pests.
But what exactly is Milky Spore and what is the best way to use Milky Spore? Is it a specific organic control or does it affect other animals like many other insecticides do? What are the advantages and disadvantages of using milk spores in your garden and lawn?
Let's explore that!
What is milky spore powder?
Milky spore powder or granules have been used for about eighty years. Source: Mike Baehr
In the 1930s, Japanese beetles destroyed ornamentals and crops in the United States so much that a national solution was needed. Scientists studying insect invasion discovered Japanese beetle maggots with white tails. They attributed the white to the so-called milk spore disease.
Then they isolated a bacterium called Paenibacillus popilliae, which causes milk spore disease.
A spore powder was developed from the bacteria that cause milk spore disease. This became commercially available in 1948 when landowners deposited milky spores en masse. Today it is used by homeowners to control infestations of the Japanese beetle and other larvae as well.
However, this bacterium is specific to Japanese beetle larvae, larvae, and adult beetles. It is not effective against other harmful maggots. Other organic insecticides attack larvae, but they do not belong to this particular strain of bacteria.
P. popilliae spores live in soils where yeast, casein and other amino acids and sugars are available. Since Japanese beetle larvae feed on grass roots and the roots of other garden plants, they ingest spore content. The spores begin to multiply in the intestines of the Japanese beetle larvae after 2 days and reach peak production after 3 to 5 days. Eventually the spores migrate into the hemolymph of the beetle larvae, a place full of food that this spore loves.
As the larvae grow and develop, the milky spore continues to infect their bodies. After 2 to 3 weeks, the milky spore populates the Japanese beetle larvae to such an extent that the rear end of the larva becomes white. Eventually, the larvae infected with milky spores die and spread the spores into concentrated populations.
Japanese beetles have seen a significant population decline since the 1940s when gardeners and landowners were advised to apply powdered milk spore. This is due to the tons of work done by scientists who individually and artificially infected Japanese beetle maggots with the bacterium.
In 1980, scientists discovered that Japanese beetles had become resistant to the milk spore bacterium and the product was withdrawn from the market. Today, an adapted form of control is approved for home use.
Interestingly, milky spore works best in areas where high concentrations (around 10 to 12 per square foot) of Japanese beetles and their offspring live. This makes a lot of sense once you learn that the overall goal of isolating the bacterium was population control, not elimination. In smaller quantities, Japanese beetle maggots don't do enough damage to require organic controls.
In addition, the spore can remain in the soil of a lawn or garden for 2 years, up to 10 years. Sometimes it can stay longer. Milky spore bacteria reproduce in living larvae, but not in dead ones. Those that remain in the ground rest as they attach themselves to grass cells and wait for more larvae to feed.
How to apply Milky Spore
The adult Japanese beetle. Source: Radu P
If you notice plants that are "skeletonized" or have all but the leaf veins eaten, it may be a sign that you have Japanese beetles (although some other insects have skeletonized leaves as well). You can treat your lawn or garden with milky spores if you've seen other signs of Japanese beetles around you.
There are two types of commercially available milky spores for treating maggots in lawn and garden areas: either in powder or granular form. You can find both in gardening and hardware stores near you. Everyone has their own method of application.
Milky spore granules come in a bag of 10 pounds or more and must be applied to the floor using a gob spreader. Fill your gob dispenser, distribute the granules evenly over the treatment area, and apply at the rate of 1 pound per 350 square feet of area.
Adjust the ratio as needed for larger or smaller areas. After applying the milky spore granules, pour them in.
It is possible to couple applications of these granules with useful nematodes. If that's your plan, distribute nematodes at the same time you water them. Apply the granules in spring, summer, and fall before the larvae hatch for best results. Most guides recommend reapplication in the lawn and garden for two consecutive years. The spore content spreads in the soil and fights a Japanese beetle infestation for up to 10 years.
Dust-like forms of this organic control come in cartons as small as 10 ounces up to 50 pounds. They have a very different method of application in gardens and lawns. Start by shaking the container to loosen up the bacteria. Then apply and pour milky spore powder in a grid pattern 4 feet apart.
Just 10 ounces cover up to 2500 square feet. If you want to apply milk spores as a powder in conjunction with nematodes, lay out the powder grid and apply the nematodes with a sprayer that pours both the dust and nematodes into the lawn or garden.
The great thing about this form of milky spores is that it lasts much longer than granules and sometimes only requires one application per decade. Some applications take 20 years.
Make sure you use this treatment in early fall as opposed to other times of the year as the food you are looking for will be active during these times.
For more information on all forms of inspection, contact the staff at your local milk spore store.
Should you use milk spore powder?
Japanese beetle maggots are susceptible to milk spore disease. Source: Travis S.
Since this disease only infects Japanese beetles, it is completely safe for all other animals (including insects and humans). Because of this, it is not useful in the garden or on lawns infested with other types of maggots.
Second, if the concentration of larvae in your lawn or garden is not high enough, the spores will not be able to multiply as easily and treatment will not take as long. This isn't a big deal unless your plants are in imminent danger.
If the larvae are still underground and have not yet emerged, there may not be any signs that your plants are in danger. Hence, it's hard to say that soil treatment is needed unless there are many bugs around.
Recent studies suggest that the virulence of this disease is losing ground anywhere in lawns and gardens. One particular study showed that the effectiveness of the treatment has decreased significantly in gardens that are not in high concentrations of the Japanese beetle.
If you are considering a lawn or garden treatment for Japanese beetles, you know you are likely to be in the long run. If you don't treat for several years in a row, your garden and lawn may still show signs of infestation.
And if you treat at the wrong time, your garden can still suffer, as the larva you want to eat with the treatment can be a few meters below the ground. There may also be better alternative treatments available.
Other methods of treatment
As mentioned in the application discussion above, nematodes (especially Heterorhabditis bacteriophora, often abbreviated to Hb) are often used in conjunction with milk spore. You may be able to omit the milky spore altogether and use nematodes instead, which are a better option if you want to control a wide variety of other pests and Japanese beetles.
Try to grow plants that are not susceptible to Japanese beetles. Plant those that are susceptible sparsely in your home so that the beetle populations cannot gain enough density to cause significant damage. Create a picture of your garden plan and add positions for endangered plants where they are separated from each other.
There are also commercially available Japanese beetle traps on the market. Floating row covers and manually plucking the beetles from your plants also work to prevent adults. A fermented fruit trap surrounded by water attracts beetles and then drowns them. They also attract and capture geraniums. Note, however, that all of these methods are designed to kill adult beetles; they don't take care of the maggots themselves.
If you've tried milky spore treatments that haven't worked, try improving the overall health of your soil and lawn instead. Mow your lawn at the highest height setting. Apply nitrogen fertilizers annually. With improved health comes improved vitality, and your lawn can potentially do beyond nibbling on the root system that maggots do.
Water well before frost and in dry periods. Instead of raking leaves and clippings, mulch them in place and leave them on your lawn to improve the soil.
frequently asked Questions
Q: Are milk spores harmful to humans?
Answer: no! The only organism that is negatively affected by milk spores are Japanese beetles.
Q: How long does it take for milk spore to work?
A: Some applications take a year to take effect. Others require up to 6 years of consistent use.
Q: Which is better: milky spore powder or granules?
A: It depends on your situation and the resources available. Dust forms require fewer applications, but granules are better for smaller areas.
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