Question
My crape myrtles were severely attacked by Japanese beetles earlier this year.  I sprayed them with Sevin which has always worked in the past.  After 3 weeks, the beetles returned worse than they were before so I sprayed them again.  Now some of the leaves have turned yellow and started dropping and they have stopped blooming.  What should I do?  Is there any hope?

Answer
Many insecticides are labeled for Japanese beetle control on landscape plants. Examples include acephate (Orthene Turf, Tree & Ornamental Insecticide), carbaryl (Sevin and many other brand names), cyfluthrin (Bayer Advanced Garden Multi-Insect Killer Concentrate), lambda-cyhalothrin (Spectracide?Triazicide?Soil & Turf Insect Killer Concentrate), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate), and permethrin (Spectracide?Bug Stop Multi-Purpose Insect Control Concentrate and many other brands). Neem extracts (Bon-Neem) deter Japanese beetle feeding but may not be adequate against high populations.



Direct spray applications of insecticidal soap kills Japanese beetles on contact but does not provide any residual protection.

Here are some points to keep in mind when using insecticides for beetle control -

Japanese beetle flight is greatest on clear days with temperatures between 84o and 95o F and winds less than 12 miles per hour. This can bring new beetles into your landscape to challenge any control program that you may have. When these conditions exist, check plants frequently to see if beetles are starting to feed again.
A few beetles on plants, or some moderate damage, will bring in more. Japanese beetles apparently produce aggregation pheromones that will attract more males and females to feed and find potential mates. In addition, volatile odors from damaged plants may attract more beetles. These conditions also can keep beetle numbers high. Keeping numbers and damage low can mean fewer new arrivals.
Japanese beetles begin to feed at the tops of plants and move down as defoliation occurs. This makes damage obvious, in terms of brown leaves and esthetic damage, but also can pose coverage problems on large trees. Hose end sprayers may allow applications to reach the target but spray drift and applicator exposure are potential problems.
Some of the effective insecticides for Japanese beetle control, such as carbaryl (Sevin) and the pyrethroids (permethrin and others) can contribute to build-ups of mites or aphids. Watch closely for signs of these pests and use acephate or malathion if needed. While these insecticides have a shorter residual life, they may help to reduce problems with secondary pests.


Repeated applications may be necessary because of the relatively short residual effect of the products. Also, a significant rainfall shortly after an application may reduce the insecticide deposit below effective levels.


Collecting Beetles
Hand collecting can be used to protect valuable plants when beetle activity is relatively low. The presence of beetles on a plant attracts more beetles. When you remove beetles daily by hand from a plant, only about half as many are attracted to that plant compared to those on which beetles are allowed to accumulate. One of the easiest ways to remove beetles from small plants is to shake the plants early in the morning (about 7 a.m.) when temperatures are low and the beetles sluggish. The beetles may be killed by shaking them into a bucket of soapy water.


I would also fertilize the tree with 10-10-10 at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. Then I would water with 1 inch of water per week-place a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop. This is called deep watering and will help the tree during the stress from the beetles.