Is there a good control for magnolia scale? A life stage (nymph or adult) and time of ;year the scale is more vulnerable? The site is full sun and the other plants in the bed are growing well but this tree is blackened and attacked every year. We practice pretty good sanitation (fall clean-up)
Good sanitation in the fall is indeed important to keep insects and fungus from propagating further. In terms of magnolia scale, or any other scale, for that matter, a bit more action is needed on your part. Since about 2010, this scale has proliferated in Toronto. The waxy coating of the mature scale insect is not susceptible to sprays, and the honeydew produced by the insect drips on everything and is attractive to wasps – an insect that has been particularly abundant this year.
September and October is the time when eggs hatch and the nymphs begin crawling. An acceptable pest control for scale is dormant or horticultural oil. This is available at most nurseries. Using a sprayer and following the directions, you can do this yourself. The oils smothers the nymphs, but has no affect on the adults that have built their waxy shield. It’s a difficult choice, as the oil can burn the leaves.
Next year, in early spring, before the leaves bud, horticultural oil can be used effectively. By following the same directions, and being aware that the day and night temperatures must be above freezing, and no rain or high winds are in the forecast, spraying the overwintering nymphs will smother them. As there are no leaves yet, the risk of burn is minimal.
Another method is less messy and can be done right away. Using your hose, a strong blast of water will knock the magnolia scale off. At this point in their life cycle, they don’t have legs, and can’t crawl back into the tree. Again, you must be careful to hit the bark, and avoid blowing off the leaves and flower buds.
Another solution, and I have done this with a different scale, is to wear gloves, and perhaps a raincoat, and pick off the scale.
Finally, if the infestation is large or the tree is big enough that you cannot do the job yourself, it may be the time to call in the professional.