Winter can be an ideal time to scout for scale on deciduous trees. The reason ‘Sooty Mold’ on the trunk or bark.
So, what is sooty mold. Sooty mold is a fungal disease that grows on bark,
(image compliments of Dr. Dave Shetlar-OSU)
leaves,
(image compliments of Dr. Dave Shetlar-OSU)
sidewalks or other surfaces.
This fungus is growing on surfaces covered with honeydew which is actually the excrements of insects that feed on the sap of plants.
This liquidly substance drips on lower surfaces and can provide a media for sooty mold to grow. The disease gets its name because it resembles soot and is black.
Not all scale will produce honeydew. There are 2 types of scale. Armored scale adults are elongated like this Pine Needle Scale
or Oyster shell scale.
These types of scale do not produce honeydew, but their feeding can still cause damage to trees and seen in this Red maple that shows premature fall color.
Soft Scale are round like this Magnolia Scale
and produce honeydew.
This honeydew drips down on the stem or trunk and can cause the bark surface to look black or stained.
(image compliments of Dr. Dave Shetlar-OSU)
But other insects can produce honeydew and are not present in the winter like aphids
although they can survive on houseplants.
Winter seems like an unusual time to be outside looking for insects. However, it is an excellent time to scout for both Soft Scale and Armored Scale. With the leaves off trees and shrubs, it is easy to find plants with signs of scale damage and scale.
As you are scouting in the nursery or landscape, plants that just do not look right can be an indicator of scale. Late summer, one of our growers noticed early fall color on Red Maples.
At closer inspections, an infestation of oyster shell scale was found.
Upon returning last week, the same infested trees are retaining their desiccated leaves. The oyster shell scale is much easier to see when the trees shed their leaves.
Pine needle scale could be seen on Japanese Black Pine, Pinus thunbergi, as well as Scotch Pine, Pinus sylvestris, and Austrian Pine, Pinus nigra. In addition,
Hemlock elongate scale was seen on Canadian Hemlock, Tsuga Canadensis.
In addition, Juniper Scale on Juniper was observed.
Since Pine, Hemlock Elongate and Oyster Shell Scale are all Armored Scale, they produce no honeydew.
Magnolia Scale
and Fletcher scale
are soft scale and produce honeydew, which causes sooty mold. Sooty mold is very easy to see in the winter since the foliage is gone.
(image compliments of Dr. Dave Shetlar-OSU)
By looking up or in on the plant, you can inspect for scale. Magnolia trunks and stems will appear black when infested.
Euonymus scale was easy to see in these top grafted plants.
The message? Now a great time to scout for scale.
Based on label recommendations, dormant oil can be effective in reducing numbers of scale. The key is to document the plant and type of scale. The location of the plants and investigate when crawlers emerge and plan to spray at the appropriate time and interval. This can be done by referring to the Growing Degree Calendar listed below.
https://weather.cfaes.osu.edu/gdd/
Another great way is to sign up by BYGL Alerts.
https://bygl.osu.edu/newsletter
Many times, authors will post the emergence of various scales while in the crawler stage which coincidentally is the easiest time to control them.
https://bygl.osu.edu/node/1803
Happy scouting.
