Question

Magnolia problem   Hi Dr. Vann,
I'm in Lansing, MI, and I have a Star Magnolia tree with either a disease or infestation.  It has hundreds of small white blobs on the branches.  They are about as big as the nail on you little finger, and are soft.  If you crush them they have mushy center but I couldn't see anything in it except for its brown color.
They tree seems unaffected but I don't know if that will continue.
Do you know what they are?  I've attached an image.
Thanks for your help.
Bob

Answer
Bob:
These "white blobs" look like insects rather than a disease.  They are probably some type of scale insect.  There are many different types of scales. These critters make their living by sucking plant juices rather than chewing or otherwise.  You will not see these insects move. Once the "babies" or crawlers find a suitable spot to feed, they will remain there for the rest of their life. If your tree is well established, it will tolerate this feeding for sometime, however as the numbers increase or if the plant gets stressed from other reasons, the tree will began to show signs of decline such as leaf yellowing and thinning of branches.

There are several effective insecticides. They include spraying the tree at the appropriate time of the year with a dormant oil (various manufacturers).  This product "smothers" the insect.  Be sure to read the temperature restrictions on the label.  If temperatures are above 85, you can get some plant injury from the spray.  There is a summer/ultra fine oil that can be used during safely during warmer temperatures. Another product, Bayer Advanced Tree and Shrub Insect Control is effective and easy to apply.  It contains the active chemical called Imidachloprid.  This product is applied to the soil around the tree watered in and is picked up by the roots.  

Check in with your local garden center or nursery for other chemical choices.  The "crawlers" are the most vulnerable life stage of this insect, so timing of sprays can be very useful in management.  Your nursery/garden center person can guide you in this area.  Be sure to read and follow the application instructions for the products.  

Unfortunately, with scale insects, they often DO NOT fall off the tree when they die, but remain on for some time afterwards.  This fact makes determining the effectiveness of an insecticide difficult.  You just have to look for new scales to see if the chemical is working.

Regards,
Steve