Mary Beth: I just returned from the East Coast where I witnessed the destructive power of Japanese Beetles. They feed on everything in their paths, chewing up flowers, cratering fruit, and skeletonizing foliage of more than 500 species of plants. They’ve just started their ravenous attack on every plant in our Block Island garden, so I thought I’d do a few tips on what to do to control these horrible little buggers.
Japanese Beetles are a problem mostly on the East Coast. They were first detected in the United States in 1916 in a nursery near Riverton, New Jersey. This voracious pest has infested 22 states east of the Mississippi River and is spreading west (hitching rides on airplanes) with isolated infestations in California, Wisconsin and Oregon. The California Drug and Food Administration inspects planes for Japanese Beetles from May to June in their efforts to try to stop them from spreading further west where the California climate and abundant food supply would be perfect for them.
Japanese Beetles mate soon after they emerge from the ground, laying their eggs in the soil. The eggs hatch in about two weeks at which point the grubs start feeding on nearby roots. It is during this period that the grubs cause the most damage to turf grass. The grubs feed all summer then burrow further down in the soil in the fall to overwinter and reemerge in the spring, feeding some more before pupating and turning into adult beetles. The adult beetles live about 30 – 50 days.
When you have Japanese Beetle grubs munching your turf roots the grass dies in big swaths that you can literally roll back like carpet. Crows are sometimes blamed for this damaged grass because they can be seen ripping up tufts to get to the grubs. They are actually helping to eliminate these pests. The grass has been long dead by the time they start looking for a tasty snack of plump white grubs, yum yum!
So what to do?
- Handpicking is effective in smaller gardens. Carry a small bucket of soapy water and knock them off the plants into your bucket as you go along. The beetles are less active in the morning and the evening so it’s easier to pick them off plants then.
- Japanese Beetle Traps — Studies have found that traps, which use a pheromone to lure the beetles, are very effective. In fact they are so effective that studies show that many of the 1000′s of beetles you will capture have come from neighboring gardens. (One step forward two steps back!) Be sure you place your traps away from your plants.
- Spraying Milky Spore on your grass is an effective long-term control and although it will not help get rid of this year’s beetles, it will kill grubs over the next two to four years. Milky Spore (bacillus popillae) is a bacterium that is ingested by Japanese Beetle grubs. The spores germinate inside the grub and multiply, killing the grubs. Over time milky spore builds up in the turf and the process is repeated over a number of years.
- Spraying with harmful chemicals is definitely not recommended. This treatment last only about 3 days and then you will have to re-spray for the next wave of beetles that are emerging, as they will continue to do for two more months. Spraying pesticides kills the good bugs (who were probably busy eating some other pesky bug) along with the bad, eventually sending something else out of whack in your garden. It also affects you, your pets, the bees that are pollinating your garden plants, and the birds that are helping to keep other bad bugs in check (birds don’t like to eat Japanese Beetles though). Worse still, it seeps toxic chemicals into the groundwater adding to the chemical load in our drinking water and in the food we eat.
There is hope for a future without Japanese Beetles. The folks at the University of California, Davis are working on developing a pheromone-degrading enzyme that could help control the beetles by interrupting their reproductive cycle. Interesting stuff — read more about it here. Let’s hope they succeed.