Insects on Boxwood and How to Treat Them
Boxwoods are everywhere and love them or hate them, they serve a purpose. Not only does their small stature make them easy to maintain but the fact that they are one of the truly deer resistant plants on the market makes them a priceless asset to our landscapes.
The abundance of boxwood being planted however has its downfall. In our quest to repel the deer from our landscapes we have created the perfect environment for another pest – insects, two of which are roaming St. Louis landscapes.
Boxwood Leaf Miner
The appearance of an adult boxwood leaf miner looks very similar to a mosquito, the adult will lay her eggs in between the two sides of a boxwood leaf and the problem begins. At this point the eggs hatch and the maggots begin to feed on the inside of the boxwood leaf, essentially ‘mining’ out the leaf and leaving it hollowed out. This causes the leaves on the plant to blister and turn yellow. I’m told that on a heavily infested plant if you listen closely enough in the spring when they are feeding it sounds like Rice Krispies crackling.
You may have noticed the leaves on your boxwood cupping. If you are seeing this then you have psyllid damage. Psyllid overwinters as nymphs inside eggs that have been inserted between the bud scales. Once the nymphs emerge they begin feeding which in turn causes the cupping of the boxwood leaves. There is only one generation of psyllids per year and the boxwood tends to outgrow any injury by mid summer.
Fortunately, there is treatment that can prevent serious damage to your boxwood. Psyllids can typically be treated with horticultural oil sprays in the spring or with a systemic insecticide.
To treat for boxwood leaf miner you will need a systemic insecticide. Systemic insecticides work from the inside out. Simply put, the plant soaks the insecticide up through the roots and kills the insects as they feed effectively knocking out the problem.