A Stroll Through the Garden: Magnolia scale and how to get rid of it

I got an email with some pictures a few years ago asking me about magnolia scale, which is a topic I have written about for a number of years. I feel confident the insect was magnolia scale. The magnolia was small. The homeowner was going to cut his losses and remove the tree. I told him in all probability he would be battling the insect for as long as he had the tree.

I love magnolia and feel the battle is worth the effort because there are new ideas out there to help. Last week I went to Secrest Arboretum and met Paul, an expert tree lover who gave me a tour of the sweetbay magnolias in the arboretum. The spectacular thing the tour was we could examine the conditions of most of the magnolias. I saw no problem with magnolia scale at Secrest with one exception.

There was a hybrid magnolia that had a mild infestation of the insect. That is quite a statement in that there are over 40 species and hybrids on the campus. Paul said they don’t spray scale insects. Instead, they allow the natural predators to do their job and their environment stays in balance.

While I was at Secrest there were some master gardeners from all over the area volunteering to prune and clean. It was great to talk to them. One of the master gardeners had a serious magnolia scale problem in her sweetbay magnolia in Canton.

Magnolia scale is a hearty soft-shelled insect

Magnolia scale, Neolecarium cornuparvum, is a soft-shell, scale insect that can have as many as three generations in one season. At the end of August we are looking at crawlers coming out of shells. This means at any time you could be fighting eggs, larvae, crawlers or adults. What can work is if you consistently and continuously attack the insects at all times with different approaches. I also have read about controlling insects in one year.

Heat can help the insect be more active. The way the insects feed is they insert their mouth part or proboscises through the cork or bark of the tree. Only a few of the adults have the power of flight. The insects can weaken the magnolia and truly kill the tree.

Magnolia scale spends the winter on one- or two-year-old twigs as tiny, dark-colored nymphs. As the temperatures warm in the spring, the scale insects begin to suck sap and molt once by early May. After May you can find males and females. Males become gnat-like flying insects, while females can become the 2-inch masses you see on the tree.

Sweetbay magnolia does the best in swamps and lowlands, which means providing adequate water and fertilizers will help it to do well and withstand attacks. The easiest solution is to prune out the limbs that are infected. The large-scale exoskeletons often remain from the previous season.

Early spring treatment can be effective treatment

Early spring treatments with a horticultural oil will be effective in controlling eggs by smothering them and breaking down the waxy coating that hides underneath. The first application should be timed with bud swelling or leaf emergence. A second application from June to August or horticultural oil at 1.5-2% after the crawlers have settled on the plants in late August should be sprayed over the affected area.

The spray should be reapplied in November and March. The oil can reduce the scale population if applied in the fall and again to kill the overwintering nymphs located on the stems. Some damage can occur to the buds. You may only have to apply for this material for one year.

A soil drench applied June to August should be repeated annually. Ants do protect scale insects so by getting rid of the ants, the predators will have a better chance at helping you get rid of the scale. Some of the predators that may help get rid of the pests are lady bird beetles (Signate Lady Bird Beetle), soldier beetles, lacewings and parasitic wasps. These insects are good guys and will help get rid of the scale. Some can be commercially purchased.

The only struggle with the good guys is that they won’t stay around if you don’t have much for them to eat. Show no mercy and give them no quarter or this enemy will take your tree. More information will be in my blog.

If you go on a stroll through your garden this week and see a challenge, e-mail me at ericlarson546@yahoo.com . You can leave comments at our website ohiohealthyfoodcooperative.org soon.

Eric Larson of Jeromesville is a veteran landscaper and gardening enthusiast and a founding board member of the Ohio Chapter of Association of Professional Landscape Designers.

This article originally appeared on Mansfield News Journal: A Stroll Through the Garden: Magnolia scale and how to get rid of it