Snails on shrub - Ask Extension
Before the snow arrived, I noticed that a limb of our Royal Star Magnolia had many small snails on it. Although there were a few snails on other parts...
Knowledgebase
Snails on shrub #857716
Asked January 23, 2024, 3:07 PM EST
Before the snow arrived, I noticed that a limb of our Royal Star Magnolia had many small snails on it. Although there were a few snails on other parts of the tree, only that limb had a large number. I used a closed hand to remove the snails and have not noticed any since that time. The snails are about 1 mm in length and none appeared to be living. Are the snails harmful and do I need to do anything to prevent their reappearing?
Dorchester County Maryland
Expert Response
These appear to be scale insects and not snails; scale can be very common outdoor plant pests, though fortunately populations that are not large tend to not damage plants to seriously. Magnolia Scale and Tuliptree Scale (as Magnolia and Tulip Poplar are related to each other) are both scale species that can use Magnolia as a host. Our Introduction to Scale Insects web page provides information about basic scale life cycles and how they feed (essentially, by sucking up plant juices). Since it's difficult to tell which exact scale this is, you can explore our Soft Scales on Trees and Shrubs page to get information about both Magnolia Scale (on that page) and Tuliptree Scale (linked from there to a separate page).
Other than physical removal, which you have done, scale insects tend to require treatment with an insecticide for long-term management if/when populations remain high enough to cause a plant stress. Indications of stress can include premature leaf shed and poor growth or dieback on individual branches with lots of the insects. There are several insecticide options, some of which are longer-lasting per treatment but which would require a certified pesticide applicator to apply as they are legally restricted in Maryland. Other ingredients can be used yourself, but they may require more frequent re-application as a trade-off. If you wish to avoid any pesticide use, simply remove what scale you can find and reach and hopefully beneficial insect predators (like a couple species of ladybug that eat scale) will help suppress future outbreaks. A low population of scale can reside on most plants without needing intervention or removal.
Environmental stress can predispose plants to scale outbreaks, such as drought (without supplemental watering) or the use of general-purpose insecticides around the yard, like sprays for mosquito suppression that (even if organic in nature) can wind-up killing some of those beneficial predators of scale and other garden pests. We're not implying this is necessarily the cause behind your outbreak, but they are common factors when scale numbers seem to rise out of nowhere. For now, you can just monitor the plant to see if or when the scale numbers increase again. Fortunately, each of the above species only has one generation per year in Maryland, so they do not reproduce quickly.
Miri
Other than physical removal, which you have done, scale insects tend to require treatment with an insecticide for long-term management if/when populations remain high enough to cause a plant stress. Indications of stress can include premature leaf shed and poor growth or dieback on individual branches with lots of the insects. There are several insecticide options, some of which are longer-lasting per treatment but which would require a certified pesticide applicator to apply as they are legally restricted in Maryland. Other ingredients can be used yourself, but they may require more frequent re-application as a trade-off. If you wish to avoid any pesticide use, simply remove what scale you can find and reach and hopefully beneficial insect predators (like a couple species of ladybug that eat scale) will help suppress future outbreaks. A low population of scale can reside on most plants without needing intervention or removal.
Environmental stress can predispose plants to scale outbreaks, such as drought (without supplemental watering) or the use of general-purpose insecticides around the yard, like sprays for mosquito suppression that (even if organic in nature) can wind-up killing some of those beneficial predators of scale and other garden pests. We're not implying this is necessarily the cause behind your outbreak, but they are common factors when scale numbers seem to rise out of nowhere. For now, you can just monitor the plant to see if or when the scale numbers increase again. Fortunately, each of the above species only has one generation per year in Maryland, so they do not reproduce quickly.
Miri
