I have a 30 year old saucer magnolia. This year sticky white patches grew all over its branches, dripping wet sticky substance. What are they and how do I get rid of them? As the tree has grown too big for the space, can I also cut off up to a third of the branches before I apply any chemicals(hopefully organic) on it? Thanks very much for your advice is advance.
Thank you for writing about your senior magnolia tree, which, as a guess, might be growing in your front garden. There are four most common varieties of Magnolia: Star, Saucer, Southern and Champaca. Saucer Magnolia (Magnolia x soulangeana) is native to France, as it was hybridized in the early 1800’s by the French horticulturalist Étienne Soulange-Bodin. For those who might not be familiar, the very precocious spring Saucer Magnolia flowers emerge and bloom — before the leaves — and measure 10-20 cm (4-8″) across, hence the saucer reference… and bloom in varying glorious shades of white, pink and maroon.
Regarding your question re pruning: as a general rule, only routine pruning to remove deadwood, and long, vertical watershoots, is recommended for magnolias. A one-third heavy pruning, as you’ve suggested, would quite possibly shock the tree, resulting in a slow recovery — and perhaps die-back. If you really need to prune to limit the size, perhaps stage this over several years, to avoid stressing your tree. If must be, always selectively prune back to a natural fork, for a healthy, and visually natural, result. If you feel you might benefit from professional arborist assistance with this project, you can easily locate a company that serves your region at Landscape Ontario’s handy search service:https://www.treesaregood.org/
Next, about the stickiness on the branches: the mature scale insect, which is most likely what has taken up residence on your tree, produces a sticky “honeydew” that drips, and attracts insects. The armoured sheath on its back is greyish-white, and at this growth stage (as opposed to the spring nymph stage) are nigh on impossible to remove. Here is a prior published TMG reply to a similar question, in specific detail, as to how you might choose to deal with your tree’s pest: https://www.torontomastergardeners.ca/askagardener/control-of-magnolia-scale/ The only chemical suggested herein is horticultural oil. The good news is that this seems to be the first year that you have noticed the scale, and so perhaps your tree is systemically stable enough to withstand the stress of the scale this season, and perhaps with diligent treatment this fall, and next spring, you can work towards eradicating this pest. All the very best to you, and your wonderful Magnolia !
For greater information regarding Magnolia’s, here is a link to the International Magnolia Society: https://www.magnoliasociety.org/Magnoliaresources