Landscape, Nursery, and Turf - More on Japanese Beetles

Japanese beetles adults will be peaking soon and then start to decline. Early to mid-July is often when we see the most severe feeding injury by adults on susceptible landscape plants. The following is an article with information on Japanese beetles and their control.

Japanese beetles are now peaking in Delaware. The metallic beetles will again find their way to our Cannas, birches, lindens, roses, etc. etc. and chew on the foliage. Feeding damage to leaves attracts yet more adult foliage feeding. Pruning out damaged foliage may help reduce repeat beetle attacks. It's no secret that sprays of Sevin, Orthene, and pyrethroids work against JB adults. Sprays of these products are typically applied every 7-10 days for maximum effectiveness. However, there are alternatives: Before emergence and heavy feeding you can targe grubs in the soil with parasitic nematodes or IGR products such as MACH2 (Halofenozide). Another option is soil drenches of systemic neonicotinoids such as imidacloprid (Merit etc.). Repellent options: The use of neem products (with azadirachtin) such as Neem-away, Neemazad, Ornazin or Azatin was recently shown to be as persistent as applications of Sevin for JB control in one study. Applications of Kaolinite Clay (Surround) are used in fruit trees for JB control although the residue on ornamental foliage may be considered unattractive. Wettable powder formaulations of some pyrethrins and pyrethroids are also reputed to have greater repellency than their EC counterparts, allowing longer intervals between re-application. Finally, have a game plan for the number of applications you'll make and the amount of damage you'll tolerate. While mid-July is certainly peak time for beetles, the need for making JB adult applications after early August should be judged critically. After this, beetle populations are already on their way down and the amount of damage they can inflict after this point will be minimal.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens