My recommendations are based on factual and research-based resources including Colorado State University Extension and the United States Department of Agriculture.
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| Internet graphic from JMB Equipment |
Spring Larvae Controls:
Following their life cycle will help in understanding when and what control products to use. Japanese beetles have a one-year four-stage life cycle (like butterflies, but JBs take one full year). The egg-larva-pupa-adult life cycle begins when the adult beetles emerge from their winter home (spent as larva and pupa) below turf grass.
When they emerge along the Front Range is anyone's guess - in the past few years they have been seen as early as mid-June. My hunch is they may emerge earlier because of the warm Denver area winter and spring. Once they are flying as adults, they begin feeding, mating and laying eggs in turf grass so the cycle begins again. Check the graphic to see how they spend each quarter of their life.
There are organic and synthetic products to use on grass turf in spring and again in the summer through fall during their egg laying period. Keep in mind that adults are very good fliers, so even if you treat your lawn, this is no guarantee they won't fly in from other neighborhoods. In large numbers JB larvae may cause turf die back as they eat their way through their grub stages, so treating the lawn is worth doing (IMO).
University and Agriculture experts recommend treating the turf as soon as the female beetles emerge and begin laying eggs. On the many edu websites and reputable sources I've read, synthetic granular grub control products may not have much killing effect on mature overwintering grubs. Pay attention to when to apply products and read all the labels for their efficaciousness.
Check out the Colorado researched fact and information sheets linked below. As a quick summary, I have written my bullet points from my April 7, 2017 Denver Post Punch List -
Denver Post Punch List - Second Week of April
- Japanese beetles have invaded certain areas in Denver, Littleton, Centennial and south into Pueblo. They are very destructive chewers of several ornamental flowers and foliage. In large numbers their larvae can cause turf die back.
- Adult Japanese beetles emerge from turf areas anywhere from late June into July. We are about two weeks ahead of spring, so consider treating the lawn now to kill their larvae.
- Keep in mind that adult Japanese beetles are good fliers so treating your lawn doesn't mean they won't fly in from surrounding yards, parks, school grounds or golf courses.
- Timing is everything, so apply grub control products soon, then again in the summer during their egg laying period.
- Look for a product that is labeled for Japanese beetle grubs (larvae). Read and follow pesticide labels, some products may need to be watered in well after application.
- Caution when using products containing imidacloprid and chlothianidin (neonicotinoid insecticides) that adversely effect pollinators like bees who visit blooming weeds including dandelions and white clover. Mow or remove any blooming plants in lawns before application.
- Products containing Chlorantraniliprole (trade names - Acelepryn or Scott's Grub-Ex) are fairly new registered insecticides that have a much lower potential hazard to pollinators than do other insecticides used for Japanese beetle larvae control.
- Biological controls including parasitic nematodes and milky spore infect and reduce larva survival. These products can be pricey and may need repeated applications for control.
- Colorado State University Extension and the Colorado Department of Agriculture both recommend using a combination of controls to reduce numbers. This includes flicking adults into soapy water, and other recommended sprays for adults and products for grubs. Traps are not recommended for adults - they attract more adult beetles to the area.
- Check out these three excellent research-based resources -
Best Management Practices Japanese Beetle USDA Colorado
CSU Department of Bioagricultural Sciences and Pest Management PowerPoint
CSU Department of Bioagricultural Sciences and Pest Management PowerPoint
For links to the other blogs I've written on Japanese beetles, please click here - Japanese Beetle Blues 2016.
