Signs of Tuliptree Scale

If your Magnolia tree is dropping a honeydew sap and turning your sidewalk and curb black your tree is probably infested with the Tuliptree Scale. The honeydew comes from the female of the species piercing the tree to withdraw sap. The sap sticks to the branches and drops to the ground, then a black sooty mold fungus develops on the tree and the ground.

Many Alamitos Heights residents Magnolia trees are under attack from this disease. It seems to be a city-wide epidemic or infestation.

Treatment and cause are illusive. Distressed Magnolia trees are very susceptible to Tuliptree Scale due to California’s long drought. The treatment to date is only about 20% effective. It requires consistent watering after the application of an insecticide.

After insecticidal treatment the treated trees need their blooms removed. This is to safeguard pollinating bees and minimize contaminating them with the insecticide absorbed by the treated tree.

This a tough problem that first appeared on the West-side of Long Beach and has spread to the East-side. On October 8th the city council approved an agenda item authorizing the Public Works Department to undertake an audit of the Magnolia trees in Long Beach. The details for the audit are outlined in a letter from Council member Uranga’s office that was signed on to by  Council members Andrews, Pearce, and our Council Representative Suzie Price. The full text of the letter detailing what the audit will look at is in the link to the letter below.

If the drought continues and we have a warm winter infection rates may continue to rise. If successful treatment rates don’t increase, we may see a long-term removal and re-planting of trees Citywide and that won’t be cheap. The best tip so far is to deep water your Magnolia trees. Let's see what an audit brings.

This Tuliptree Scale treatment summary is not designed to provide a detailed how-to and it is not definitive. It is designed to illustrate some different approaches to treating infected trees.  We look at environmentally friendly approaches and commercial chemical treatments with possible environmental side effects. We have some approximate costs for the commercial treatments. 

We know the Tuliptree Scale attacking our beautiful magnolia trees is a soft-shell scale and it seems to proliferate in the late summer and early fall.  One of several things making this pest hard to get rid of is it latches on to the tree by piercing it then sucking the life out of the tree. As the scale procreates there can be a multitude of scale in various stages of development waiting to mature and attach to the tree. This makes it more challenging to control and defeat the scale.

Let’s look at more environmentally friendly controls for scale.

1. Deep water the tree

1.1 Use the Corona Root Irrigator Model LG 3710 about $25

1.2 Or set up an Emitter tubing system like Rain Bird offers

1.3 Consider an emitter or bubbler system with RainBird’s Root Watering System

1.4 For more information on RainBird products see the pdf file below

2. Wash the tree with the garden hose water it may help

3. Spray the tree with horticultural oils like Neem Oil wetting down the stems and leaves 

3.1 For more information on Horticultural oils see the pdf file below

4. Spray with insecticidal soap to fight the crawlers. This may not affect the mature adults. 

4.1 For more information go to https://www.thespruce.com/how-to-use-insecticidal-soap-1902893

5. Here is another how to resource at https://www.thespruce.com/how-to-get-rid-of-scale-insects-1402693

6. Manually scrape the scale off the tree using a knife or fingernail

Let’s look at chemical treatments a commercial tree pest control company might offer. 

The costs vary based on the diameter of the tree, the treatment chosen, and the number of trees treated at one time. Determine the size of your tree by measuring it’s circumference at about 4’ off the ground then divide by 3.14 to get the diameter. The smaller the diameter the less chemicals applied, and the cost is less, and the bigger diameter trees will cost more.

Here are 4 possible chemical treatments and some rough estimates of costs associated with them.

1. Soil Surface Treatment places a chemical in the soil for the roots to absorb. It requires watering after application, so the tree absorbs the chemical. As the scale sucks the tree sap, the chemicals are absorbed by the scale and kill the scale

1.1. Cost is very roughly $0.75 per inch of tree diameter

1.2. Possible negative impact is contamination of soil and any run off to the surrounding soil and gutter

1.3. Possible negative impact on pollinators

2. Injection Treatment method is where holes are drilled around the base of the tree and the chemicals are introduced and absorbed to attack the scale as they suck tree sap

2.1. The cost is very roughly $10 per inch of tree diameter

2.2. A possible downside of this treatment is if multiple applications are required, drilling multiple sets of holes in the base of the tree may compromise the tree itself

3. Over Head Spray Application would require 2 treatments about 2 weeks apart. Rain could wash the chemicals off the tree leaving it without protection

3.1. The cost will vary based on the tree diameter with a range from about $80 to $300

3.2. Possible negative impact is contamination of the surrounding air and any run off to the surrounding soil and gutter

4. Basal Application is coating the tree bottom 4’ of the tree with a chemical that is absorbed by the tree and attacks the scale.

4.1. Cost is very roughly $6 per inch of tree diameter

4.2.  Possible negative impact is contamination by run off to the surrounding earth and gutter

4.3. Possible negative impact on pollinators

There doesn't seem to be an easy button to hit to irradicate the Tuliptree Scale, however the City of Long Beach Public Works Department will soon release their audit and report very on this difficult problem.