Scale infestations injure magnolias

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I have a couple of magnolia trees that look like what you described in last Friday’s column. In addition to shedding and drooping leaves, the leaves have tiny white specks on them. What is this, and is there a treatment you can recommend? From Marshal

A: The tiny white specks you see are called false oleander scale. We did not see a lot of the scale on magnolias until two or three years ago. It probably showed up a couple of years before that in the Augusta area, but on such a small scale that it was not that noticeable. Augusta Richmond County Extension Program assistant and retired Aiken Extension agent Suzanne Holmes told me they have been in the Charleston, S.C., area for about 10 years.

False oleander scale was first described in California from quarantined palms from China. It was first found in Orange County, Fla., in 1942, so it is not that new to the United States.

It was formerly called magnolia white scale. There are many types of scale insects. This one is referred to as an armored scale. They are really tiny, varying in size from 1 to 3 millimeters.

Over time, the false oleander scale can weaken a tree. Their feeding causes chlorotic spots that are visible on the upper leaf surface. These spots are usually several times larger than the scale. Heavy infestations can cause the entire leaf to turn yellow and drop prematurely.

False oleander scale is probably not a good name for this insect because it has many plant hosts and the numbers will more than likely increase over the years. Plants it can infect include flowering dogwood, oleander, banana shrub, sweet bay magnolia and aucuba.

All life stages of the scale may be found throughout the year.

Armored scale such as this one can be difficult to control when it is mature. Examine plant leaves for live scales by crushing the wax cover. Dead scales do not fall from the plants, so even if they are killed, it will take a year or two for them to fall off.

Horticulture oils are one of the best insecticides to use for control but are not practical in most cases for larger trees because of their height. If spraying, time the sprays to coincide with the crawler stage in the spring, normally during May and June.

For taller trees that cannot be sprayed easily, you can use a couple of systemic insecticides that are applied to the root system of the tree. One has the active ingredient imidacloprid and is sold in most retail stores as Bayer Advanced Tree and Shrub Insect Control. Many people refer to it as Merit.

The other option is the insecticide with the active ingredient dinotefuran, sold as Safari. The only two places I am aware of that sell this in the Augusta area are John Deere Landscapes and Nurseries Caroliniana. John Deere Landscapes’ product is packaged more for commercial operators, while Nurseries Caroliniana’s is for homeowners.

Safari will provide a much quicker kill than the Merit. Based on some research from Clemson, you can expect about an 80 percent kill within six weeks with Safari while it might take up to one year to get the same results from the Merit. As far as cost, Safari is more expensive than Merit.

For immediate results on trees with long, hanging limbs and where the scales on the trees are most visible, you can spray now with the horticultural oils.

LEAF GALL: Leaf gall is occurring on sasanquas, camellias and azaleas. Leaf gall is a condition where the new, expanding leaves become thicker and larger and usually have a pinkish/green color on the upper leaf surface. The lower leaf surface will eventually turn white when the fungus is releasing the spores. Infected leaves dry and turn brown to black in late spring.

The disease affects only the new growth, so older leaves are resistant to the infection. Leaf gall is always worse when we have a cool, wet spring. Under dry conditions and sunny locations, the disease is seldom seen.

Remove and destroy diseased leaves before the lower leaf surface turns white. This will reduce the inoculum source for next year’s infection. Don’t leave the infected leaves on the ground after pruning because the spores can spread from the infected clippings.

Fungicide applications are seldom necessary and will provide only limited control. They must also be made as leaf buds swell in the spring, and we have already passed that time. Since this is not a major disease and not prevalent every year, I don’t recommend spraying preventatively unless you have one or two prized plants in a high-profile area.

REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.


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