Magnolia scale females have given birth to live young, and these tiny, dark crawlers have started to venture out to feed on twigs in the landscape. Signs of magnolia scale include honeydew: sticky leaves and sticky residue on vehicles and outdoor furniture underneath infested trees; Ants and Wasps attracted to the honeydes; Black sooty mould growing opportunistically on the honeydew residue; and of course, foliar chlorosis and premature leaf drop from the feeding damage.
Pick off scales to reveal dark grey crawlers (eggs with legs) underneath. Many crawlers will hide underneath the female scales for days before they venture out, meaning they are protected from insecticide applications in the first week or so.
The crawlers will gradually emerge out from under the dead female mothers. Contact insecticides (traditional insecticides, insecticidal soap, horticultural oil) can be used to manage crawlers once they emerge and start feeding on twigs (mid-late August). Multiple applications will likely be necessary to manage all crawlers, 2-3 times about 7-10 days apart.
In the landscape, insecticide applications (e.g. insecticidal soap, horticultural oil, or traditional insecticides) can be used if you are trying to manage the crawler stage of this pest.
If you miss the Magnolia scale crawlers in August, don’t stress.
Nymphs overwinter as tiny, dark grey scales on the undersides of twigs. It is advisable to treat with dormant rate, horticultural oil sprays (with emphasis on contacting undersides of twigs) in October to significantly reduce the population in late October. Try to time your applications to late leaf drop to maximize coverage on twigs.
Many horticulturalists say that fall dormant oil applications are the BEST way to manage this pest issue, even more effective than spring dormant oil applications.