I have a Jane magnolia tree. This year, it has developed large white spots all over the branches. Also, it has been emitting a sparkly fluid on the leaves, attracting ants, flies, and bees of every kind. Do you know what's causing it and how to treat it? Thanks.

Hi Nancy,

Your magnolia has an insect called scale.

The magnolia scale, Neolecanium cornuparvum, is one of the largest and most conspicuous scale insects known to occur in Ohio. Adult females may reach nearly ½ inch in diameter when fully grown. This soft scale is shiny, tan-brown and smooth. As the scales grow, they are often covered with a white mealy wax. This wax is lost at the time that the crawlers emerge.

There is a way to distinguish armored and soft scales. Armored and soft scales suck different fluids from plants. You can tell what a scale insect is eating by what comes out the other end. Armored (hard) excrete very little, soft scales feed in plant phloem, which is rich in sugar, so they excrete lots of a shiny, sticky fluid called honeydew. Honeydew accumulates on leaves, sidewalks, cars and decks beneath soft scales and other phloem feeders like aphids, whiteflies and mealybugs. Besides making things sticky, honeydew is also a substrate for black sooty mold fungus. So, look around your suspect scale insects for honeydew or black sooty mold. If leaves beneath the scales are dry, you probably have armored scales. If they are shiny or sticky, you have soft scales. Your description seems to indicate soft scales. The honeydew may also attract ants, bees, wasps and flies that feed on it.

Horticultural oils, often called summer oils, at the label rate applied after the crawlers have settled in late August can be very effective in reducing the scale population. Be sure to thoroughly wet down the stems and leaves. Be sure to read all the directions carefully.

Horticultural oils are pesticides that control insects, mites and some plant diseases. They are specifically designed to control plant pests. Commercially available horticultural oils are highly refined petroleum products that are filtered and distilled to remove compounds that can harm plants. Neem oil is a type of horticultural oil. Vegetable oil, mineral oil, and highly refined oil are all other types of horticultural oil.

Neem oil is often used as a multipurpose pest and disease control in the garden. Neem oil contains a natural chemical called azadirachtin that other horticultural oils don’t have, which allows it to be more effective at pest control than other oils. Still don’t use neem oil on stressed plants, including new transplants or plants that are wilted or need water.

Applying this product in calm weather when rain is not predicted for the next 24 hours will help to ensure that wind or rain does not blow or wash pesticide off the treatment area. Do not apply when temperatures are excessively high (above 100 degrees F) or low (below freezing) or while the tree is in bright sunshine. Depending on how bad the infestation is, you could also consider pruning out the most heavily infested branches. Rinsing application equipment over the treated area will help avoid run off to water bodies or drainage systems. It is a good idea to test the product on a small area first.

As for dormancy, a single dormant oil spray will achieve excellent results against most soft scales,

Live vs. Dead Scale Characteristics:

Probably all too often, dormant oil treatments are applied to scale populations that are not viable. Just a little bit of extra time is required to determine if the observed scales are dead or alive.

Compare a live, viable scale insect to a water filled balloon. If the cover is somewhat flexible and soft to the touch it may still be alive. Furthermore, with the use of a sharp pinpoint (e.g., insect mounting pin), determine if insect body fluids are released. When the waxy cover of a live armored scale is removed from the plant surface, it will often appear as a red/yellow “blob of jelly”.

CHEMICAL CONTROL IS A LAST RESORT BECAUSE OF THE ENVIRONMENTAL ISSUES

A variety of insecticides if applied when the insects are in the freshly settled crawler stage. This is usually in late August to early September. Sprays applied before the crawlers are present or after they have become dormant in the overwintering stage will have little effect. When applied in early May, soil drenches with systemic insecticides have provided excellent control. Always read and follow label instructions.

Additional reading:

https://ohioline.osu.edu/factsheet/ENT-61

https://extension.unh.edu/blog/2020/01/what-should-neem-be-used-plants#:~:text=Regardless%20of%20the%20type%20of,on%20a%20small%20area%20first.

https://plant-pest-advisory.rutgers.edu/a-primer-on-dormant-oil-applications/