Azaleas are perhaps the most popular landscape plants in Augusta.
For the most part, azaleas are pretty carefree when it comes to maintenance. But we do have a little insect called the azalea lace bug that is probably the biggest nemesis. Most of the time there is no predicting if the lace bugs will show up on your azaleas. In some areas, people never have a problem, while in other locations, azaleas are severely attacked. Most seem to be more susceptible when they are in too much sun, although this is not always the case. If you have a problem with lace bugs, I am going to help you plan your strategy for control.
The nymphs (young stage) and adult lace bugs live on the underside of azalea leaves. They damage their hosts by piercing the leaves and destroying the plant cells. Infected leaves look stippled from above. On the undersides, they’re discolored with dark, varnish like excrement and cast-off insect skins. Infected plants are weakened and look bad. When many people describe the damage to me, they say “my leaves look white.” This is because the lace bugs have sucked out much of the chlorophyll.
In the past, control programs for lace bugs relied heavily on insecticides. These products often had to be applied to infested plants several times during the growing season. And control results were marginal.
In the landscape industry and even for homeowners, we like to promote the Integrated Pest Management approach for controlling pests on ornamental plants. IPM stresses fewer pesticides and relying more on biological control and cultural practices.
Research that has been done in the past helps to provide some answers in controlling lace bugs with less pesticide applications per season.
Research shows that there are four generations of lace bugs each year. The insects overwinter in the egg stage. The eggs are beneath the black, varnish like excrement on the undersides of the leaves. These eggs normally hatch in early to mid-March, and the nymphs begin to feed and develop. This first generation of lace bugs develops by late April.
Adult lace bugs are then present all season, laying eggs to build the population. The three succeeding generations also continue to lay eggs, and you will be able to find all stages of lace bugs on infested plants. Adults of the fourth generation are mature by the end of September. In mild winters, they can be found throughout December. The eggs that these adults deposit are the ones that overwinter.
To control lace bugs, consider what I have said about the insects’ life cycle. You can see that you need to time your insecticide application from late March through early April. This will control the first generation of lace bugs and this in turn will reduce the need to spray again the rest of the year.
Lace bugs are easily controlled with a variety of insecticides including insecticidal soaps and horticultural oils if you get good coverage.
Remember you have to spray underneath the leaves. If you don’t want to have to spray underneath the leaves or if your azalea bed is large, consider using an insecticide with systemic activity such as acephate (Bonide Systemic Insect Control). You can also use imidacloprid (Bayer Advanced Tree and Shrub Insect Control). With this insecticide you mix the liquid with water and pour it around the plants. For the granular version just sprinkle on the ground and water it in. This will give you season long control but it can be an expensive treatment for large azalea beds. The acephate will typically give you about six week’s control. But again, if you control the first generation, you should not have to apply these products more than once.
Research has shown that damage as high as 13 percent of the azalea foliage by lace bugs has no effect on plant health or subsequent flowering. Tolerating minor damage without spraying encourages the build-up of natural predator insects that can keep lace bugs at low levels.
I probably have over 100 azaleas in my yard and there are very low populations of lace bugs so I don’t need to treat them.