Magnolias are an exceptional show stopper in the urban landscape. In Southern Ontario, they are a small to medium sized tree, ranging from 10–30 ft tall, depending on the variety. They are most recognized for their beautiful flowers that range in different colours and sizes. Their foliage is a light shade of green and their bark is gray and smooth. Unfortunately, owning these trees may come at an extra cost, as they are the host species for Magnolia Scale (neolecanium cornuparvum).
Magnolia Scale Facts
The Magnolia is the only host species for Magnolia Scale. Most common types of Magnolias in southern Ontario are Saucer, Lily and Star. There are many other varieties or hybrids that are less common but all are still equally at risk of Magnolia Scale.
The Magnolia Scale is one of the largest scale insects in Southern Ontario. There are two categories, soft and armored or hard-shell scales. The easiest way to compare the two is the presence of a sticky substance called honeydew. This is only produced on soft shelled scales. Soft scales are also larger than armored scales.
Heavy infestations will cause decline in the host tree. Multiple years of infestations will cause complete fatality of the host. The honeydew left from soft scales can also grow a black sooty mold. This will stain the tree in black and can create a mess underneath the canopy. The honeydew is sweet and will attract other insects. The most common and nuisance one being wasps.
Insect Life Cycle
Per a season, there is one complete life cycle or generation of the Magnolia Scale. Starting with the nymph, this is when they are overwintering in branches of the host tree. They will overwinter here from September to July. Depending on the weather, they will emerge in the month of July. The males and females will mate, continuing the cycle. The males die soon after mating while the females remain a short while later to give birth to our next stage which is referred to as the crawler stage. This takes place in August – September. The crawlers will again find branches that are typically 1–2 years in age and overwinter till July of the following year.
Magnolia Scale Treatment Options
In small infestations, where the Magnolia scale is found on select branches, pruning and removal of these branches will help cut the cycle of the pest. In moderate to heavy infestations, pesticide sprays are an option. A Dormant Oil in the Spring will help reduce infestation. A Insecticidal Soap or Dormant Oil may also be used in the early parts of the crawler stage from August to September.