Milky Spore - Ask Extension
Does Milky Spore powder need regular watering to work well? I applied the powder about a month ago and watered it right after. There has not been mu...
Knowledgebase
Milky Spore #815629
Asked October 31, 2022, 2:58 PM EDT
Does Milky Spore powder need regular watering to work well? I applied the powder about a month ago and watered it right after. There has not been much rain since then. The lawn is full of weeds so I am going to put down plastic soon to kill the weeds and then plant grass in spring. But in putting down plastic I wonder whether the milky spore will continue to do its job without any moisture. This is our 2nd application of milky spore. that got rid of most of the grubs, but there's still a few in the soil.
Thanks, Ann Pannier
Hennepin County Minnesota
Expert Response
Despite marketing claims to the contrary, university-based research indicates that milky spore isn't likely to control Japanese beetle grubs in Minnesota and other northern states. The following publications explain why:
https://arboretumnaturenotes.wordpress.com/2020/07/07/japanese-beetles-theyre-back/
https://extension.illinois.edu/blogs/rhonda-ferrees-ilriverhort/2015-06-29-japanese-beetle-myth-information
According to the following excerpt from a Colorado State University publication, milky spore effectiveness may even be minimal elsewhere.
"Milky spore is applied to turfgrass areas where Japanese beetle grubs are active and may infect some of the grubs, producing a chronic infection that reduces survival and reproduction. Applications of milky spore powder will not produce immediate reductions in number of Japanese beetles; if an application of milky spore is able to result in successfully infecting some grubs, then milky spore will continue to reproduce and spread on its own. In areas of the eastern United States, where milky spore has long been widespread, it annually infects a small number of grubs, resulting in some reduction of the Japanese beetle populations (less than 5%)."
Go here to read the entire publication:
https://extension.colostate.edu/topic-areas/insects/japanese-beetle-5-601/
In any case, follow product label instructions regarding watering to achieve potential milky spore benefits.
Under current Twin Cities area conditions it's worth noting the Japanese beetle grubs do not fare well during persistent drought. Unless the lawn has been watered well and has not gone dormant, drought may limit grub numbers more than insecticides or milky spore.
Also, please note that covering the lawn over winter with plastic isn't likely to kill perennial weeds such as dandelion, plantain, thistle, quackgrass, etc.
https://arboretumnaturenotes.wordpress.com/2020/07/07/japanese-beetles-theyre-back/
https://extension.illinois.edu/blogs/rhonda-ferrees-ilriverhort/2015-06-29-japanese-beetle-myth-information
According to the following excerpt from a Colorado State University publication, milky spore effectiveness may even be minimal elsewhere.
"Milky spore is applied to turfgrass areas where Japanese beetle grubs are active and may infect some of the grubs, producing a chronic infection that reduces survival and reproduction. Applications of milky spore powder will not produce immediate reductions in number of Japanese beetles; if an application of milky spore is able to result in successfully infecting some grubs, then milky spore will continue to reproduce and spread on its own. In areas of the eastern United States, where milky spore has long been widespread, it annually infects a small number of grubs, resulting in some reduction of the Japanese beetle populations (less than 5%)."
Go here to read the entire publication:
https://extension.colostate.edu/topic-areas/insects/japanese-beetle-5-601/
In any case, follow product label instructions regarding watering to achieve potential milky spore benefits.
Under current Twin Cities area conditions it's worth noting the Japanese beetle grubs do not fare well during persistent drought. Unless the lawn has been watered well and has not gone dormant, drought may limit grub numbers more than insecticides or milky spore.
Also, please note that covering the lawn over winter with plastic isn't likely to kill perennial weeds such as dandelion, plantain, thistle, quackgrass, etc.
