Q: I recently read an article about using a product called “Doom” to control Japanese beetles. How does this stuff work? Is it effective?
A: “Doom” contains a bacteria that infects Japanese beetle grubs with a disease that turns their internal fluids white. For this reason, the disease the grubs get from contact with the bacteria is called “milky spore disease”. Fortunately for us, the bacteria only affects Japanese beetle grubs.
That’s the simple answer to a more complicated question. Before you use milky spore disease, you must determine if you have the grubs of Japanese beetles or June beetles or May beetles or masked chafer beetles. The information is important because the disease (BI)only(EI) affects Japanese beetle grubs – not the others.
Second, you must have a high population of Japanese beetle grubs present in order for the spore to spread throughout the soil and maintain its grub killing activity.
Third, even if you kill all of the Japanese beetle grubs in your lawn, what about the adult beetles that fly in from your neighbors’ lawns? The beetles can fly several hundred yards in search of a scrumptious rose bloom or a tasty crape myrtle leaf. How will you control them? Grub control on your own lawn will come to naught if your neighbors are not also vigilant.
In my view, it is easier and cheaper to hand-pick adult beetles from infested plants when populations are low and to consider using least toxic pesticides (but never traps) when beetle populations are high.