How Horticultural Oil Saves Your Trees & Shrubs from Scale

By January 19, 2018Plant Care

When you walk around your property, do you look at the undersides of your shrubs and ornamental trees?

Do you notice that your ornamental woody plant leaves are mottled?

Have you noticed a sticky substance on the branches and leaves of your favorite hollies or southern magnolias?

Then you may have scale. As you’ll learn later in this blog, scale—both soft and armored—can cause a lot of damage to your trees and shrubs. But horticultural oil is the best defense to keeping your landscaped trees and shrubs from destructive scale.

What is scale?

Scale are tiny insects that attack ornamental trees and shrubs as well as groundcovers and turfgrasses.

Both types of scale can be found on the undersides of leaves and stems of plants. There are two types of scale:

  • Soft scale: This scale has a fish-like covering which gives it the scale name. Females lay eggs under their bodies and then die. Their offspring, called crawlers, hatch in the spring and eat plant sap to help them grow and reproduce.


Soft scale also excretes “honeydew,” a sticky substance that will turn moldy, called sooty mold.


  • Armored scale: This scale has a heavier cover compared to its soft scale cousins. It’s also smaller in size.

Plus, armored scale doesn’t secrete any honeydew and doesn’t contribute to sooty mold. However, they, too, eat plant sap causing your ornamentals to weaken, lose leaves and other symptoms.

How You Can Know if You Have a Scale Problem

Your trees and shrubs will show symptoms of armored or soft scale. Here are five common signs of scale damage:

  • A black, sticky mess underneath your plant’s stems and leaves – Soft scales are easier to catch because of the honeydew that’s left behind. This honeydew turns moldy, leaving a black, sticky mess.


  • Mottled leaves – In the beginning, you may notice that your leaves look mottled yellow on the stems and leaves. This is the first sign that you may have a scale problem.


  • Yellowing leaves – Infected tree and shrub leaves turn yellow before autumn.


  • Premature leaf drop These yellowed leaves drop from trees well before autumn.


  • Branch dieback You notice that not only are leaves missing from the tree, but you have more dead limbs on the infected tree or bush.

You don’t want your ornamental trees and shrubs to get to the point of premature leaf drop or branch dieback because the plants are now in a weakened state.

Additionally, your shrubs and trees are more susceptible to a secondary insect infestation as well as certain plant diseases due to scale damage.

Read how persistent cold can damage your perennials and other plants.

How You Can Prevent Scale from Infesting Your Trees and Shrubs

The best way to prevent scale from infesting your landscape trees and shrubs is to keep a close eye on them.

Also, if you hire a lawn and landscape maintenance company, the technician will do a weekly inspection of your ornamental woody plants looking for signs of scale as well as other insects and diseases.

Also, your technician will advise you not to overdo fertilization because it makes your trees and bushes more susceptible to scale.

Tree and Shrub Recovery

If your trees and shrubs suffer from scale, the best that you can do to keep your plants alive is to employ plant health care (PHC). Trees and shrubs that have had insect infestations can survive when they have the following:

  • Adequate watering – Just like your lawn, your trees and shrubs need a once or twice a week soaking rather than a daily sprinkle.


  • Appropriate fertilization – If your ornamentals are on the lawn where they get some of your lawn’s fertilization, they probably don’t need additional fertilizer. Too much of a good thing produces the opposite effects—disease and insects.


But if you have trees and shrubs in garden beds and borders, then you’ll need to add some fertilizer to provide necessary nutrients that may not be available to them.


  • Inspection – Make sure you inspect your woody plants every week. Look on the undersides of leaves and branches to see signs of insect activity.


  • Properly prune your trees and shrubs –There is definitely an art and a science to trimming your trees and shrubs. If you don’t have the time or don’t know how to properly prune, hire a professional to complete that task for you.


  • Think about hiring a professional landscape maintenance company – When you hire a landscape maintenance company to provide plant health care to your trees and shrubs, you know you’re getting the best advice and care available. PHC technicians will inspect your plants every time they visit your property. And they’ll give you the advice and direction you need to go to have the healthiest plants possible.

How Horticultural Oil Suffocates Scale and Other Insects

The best way to get rid of scale and other harmful insects is horticultural oil. Your lawn and landscape technician will expertly apply horticultural oil to your infected trees and shrubs.

Horticultural oil will suffocate these insects to stop them damaging your woody ornamentals. There aren’t insecticides on the market that successfully remove scale from your woody ornamentals except for crawlers.

Learn more about horticultural oil, also known as dormant oil, in this blog post.

So, keep an eye out for scale and other harmful insects. Hire a professional to apply horticultural oil to both protect your plants from scale as well as to get rid of existing scale. Make sure you employ solid plant health care so your trees or bushes can recover and produce leaves in spring.

If you need a PHC technician to apply horticultural oil and other plant services, call us today at Agropro, 678-445-9990 or fill out our contact form.

Agropro Lawn Care ~ Lawn specialists serving these North Georgia cities: Alpharetta, Atlanta, Buckhead, Canton, Cumming, Dunwoody, Johns Creek, Marietta, Milton, Roswell, Sandy Springs and Woodstock.