How can I deal with Japanese beetles destruction on my roses? Bug dust doesn’t really help.
The Gardener’s Answer
Hi, Jennifer: Japanese beetles can be a real nuisance and make our plants look skeletonized and in severe cases can completely defoliate a rose. These pests feed on more than 300 species of plants but roses seem to be one of their favorites. Understanding their life cycle is helpful in terms of control. Adult females stop feeding midday and burrow a few inches deep to lay their eggs. These eggs eventually turn into grubs and for the next 10 months they feed on grass roots, and then pupate into the unmistakable adult beetle that emerges in late June and feeds for about four to six weeks, dying soon after. The adult beetles only live for 30-45 days. Adult beetles tend to feed in large groups, making the damage more noticeable and unsightly. Controlling them in the grub stage can be tricky because we do not always know where they are living. A good indication would be areas of dead turf, and in this case a soil insecticide used at the proper time can be effective. It is obviously easier to control them as adults because we can see them. Hand picking is very effective and environmentally friendly. Grab a bucket of soapy water and go out in the early morning when they are not very active and literally hand pick them off your rose and dump them into your bucket. There is actually something very satisfying about this although it may not be feasible with large infestations, but certainly doable with a few roses. Other options include insecticides with the main ingredients being pyrethroid or carbaryl. Both are effective if used properly and as product instructions indicate. Timing is everything in controlling these beetles and these products will need to be applied more than once. Neem is a botanical option that will last for a few days and then will need to be reapplied, but is safe for bees and other beneficial insects. Adult beetles are attracted to plants that are already infested, so reducing numbers is a good way to deter other from flying in. Protecting your rose with cheesecloth is another option during the four to six weeks when the beetles are most active. Unfortunately these beetles are here to stay but it does not mean we have to stop planting roses. Avoid using beetle traps since these products only encourage them to enter your garden.