Magnolia Scale Just Sucks
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If you haven't come across Magnolia scale (Neolecanium cornuparvum) yet this year, consider yourself fortunate. In my area it is absolutely rampant. We're seeing Magnolia Scale on a majority of non-native magnolia trees. Infestations are heavy and, knowing how this pest goes, I expect it will only get worse since we are approaching egg hatch time on the phenology calendar.
Magnolia Scale and Tuliptree Scale (Toumeyella liriodendri) are native “soft scales” (order Hemiptera, family Coccidae). Magnolia Scale sucks sap out of the magnolia stems while hiding under a shell which is plastered to the stem. I describe it to my clients as ‘little turtles plastered against the stems of the plant and sucking the life out of it.’
The insect is really only interested in the proteins in the sap, which are not too abundant, so once those are extracted the insect essentially gets insect diarrhea and poops out the rest, a sugary sweet excrement that entomologists call honeydew. I guess that's supposed to sound better than ‘bug crap’. The honeydew drips down on leaves, branches, and anything in the area attracting all manner of insects which are coming for the free sugar water.
Infested trees are often swarming with wasps, bees, yellow jackets, flies, ants, and any other critter which happens to enjoy sugary fast food. Sooty Mold fungus, aptly named due to its black color, grows on the droppings and turns leaves, branches, and everything under the infested tree black. Most clients are not real crazy about this side effect.
Interestingly, the ants will often farm the scale insects, protecting the insects from predators and preserving their food source. One method which has been used to curtail Magnolia Scale is to put sticky bands around the trunks. This prevents the ants from accessing the scale insects and protecting them from predators, allowing the predators to feed on the scale and cut down the populations to a manageable level. It has been reported that these sticky bands can sometimes be sufficient control without having to do anything else.
Should this not be sufficient insecticide treatments are certainly an option. We use a combination of systemic insecticides such as Dinotefuran and Imidacloprid, as well as insect growth regulators and oils. Of course, you need to be careful with any oils in this hot weather. Horticultural oil in the winter can help to take care of scale insects which are overwintering on plants.
I like to tell clients that treatment for Magnolia Scale, even though it's an insect, is analogous to treatment for cancer in humans. You generally don't just get one chemotherapy or radiation treatment but rather a series. If you get rid of it in one treatment that's a bonus but that is often not the case.
What is interesting is that we really only see Magnolia Scale on the non-native magnolias. This is because Magnolia Scale is a native insect and native insects generally do not cause as much damage to native plants because evolutionarily the two grew up together. If native insects wiped out their hosts it would not be a very good strategy.
I have never seen Magnolia Scale on a southern magnolia (Magnolia grandiflora) or a sweetbay magnolia (Magnolia virginiana), both of which are native. I have seen other species of scale on these magnolias but not generally in very large numbers. I have seen small amounts of Japanese Maple Scale on sweetbay magnolia.
In addition to the Magnolia Scale, we are seeing mildew disease on magnolias. This is a result of the wet and damp conditions this spring. Mildew causes aesthetic damage and discoloration to the leaves but generally does not harm the plant significantly. Like most diseases, mildew is prevented and not cured so the cat is out of the bag with this one as well when it comes to treatment options.
Magnolia and Tuliptree Scales from the BYGL
Magnolia Scale (Neolecanium cornuparvum) and Tuliptree Scale (Toumeyella liriodendri) are native “soft scales” (order Hemiptera, family Coccidae). Coccids are called soft scales because the females are hidden beneath a helmet-like soft leathery covering that provides some protection. However, they are easily crushed.
