Nursery, Greenhouse, and Landscape News

Can Milky Disease Control Japanese Beetle Grubs in the Field?

Until recently, milky disease, Bacillus popilliae Dutky, has been for sale under the trade names Doom and Japademic. Commercial products were produced by injecting healthy grubs with the disease. Though at present these products are no longer available, the ability to effectively use this bacteria to control Japanese beetle grubs in the field is questionable. Like other native milky diseases attacking root feeding grubs, B. popilliae infects Japanese beetle grubs when they consume bacterial spores while feeding on roots in the soil. These spores germinate in the gut from where bacteria invade the rest of the grub and kill it over a period of several weeks. At the end of this process, the grub's blood becomes filled with billions of white spores that give the normally clear blood a milky white appearance. Because viable spores persist in the soil, introducing the spores into a population of Japanese beetle grubs can spread the disease and ultimately control the grub problem.

Although lasting control of high grub populations (>10/ft2) have been reported within 1-3 years after applications of a commercial preparation, control in the field has been variable. Researchers at the University of Kentucky tested commercial preparations to examine causes of this variability. Laboratory tests using Doom showed that this formulation was moderately infective with 39-44% of grubs becoming infested. Large scale field tests conducted in plots with pre-existing Japanese beetle infestations failed to link milky disease to lower grub populations during the 3 and a half year study. Small plots, artificially infested with grubs, and laced with milky disease according to manufacturer recommendations also failed to reveal disease symptoms over a 17 month period. Finally, grubs infected with milky disease were found to consume the same quantity of roots as uninfected grubs.

In summary, milky spore preparations were found to be ineffective when used according to label directions in the field. Reports of success by previous researchers were limited to very high infestations of grubs where other stresses may have increased their susceptibility to diseases. The only good news to report is that the commercially produced milky disease spores were able to infect grubs in the laboratory. The challenge that remains is to figure out how to get it to work in the field.

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