Farmers Weekly Review

I know many of you have had it with the buzz of the male cicadas calling for their sweethearts over the last month, but they are literally harmless to our plants. But there is a silent killer among us. Even worse, they are difficult to detect, almost until it is too late.
Magnolia scale, like the other scale insects, is very difficult to detect. As adults, they drop off their legs and permanently seal themselves to the stem of a plant. In their juvenile form, they are able to move, scurrying about the branches, looking for their permanent home.
Fortunately, as far as scale goes, the female magnolia scale is the largest scale we have. They can be up to one-half inch long and round to oval, and grey/green to pink. And are shaped kind of like a World War II helmet.
The mouthparts of scales are the vampire-like piercing sucking mouthparts. And they start to suck the nutritious plant juices out of your plants. Silently reducing the food your plant’s roots are sending up to those outermost branches.
As if that wasn’t enough, the plant juices scales intake, well … let’s just say, what goes in must come out. And the insect “honeydew” (the polite name we give to insect excrement) is very sticky. And can coat the ground, patio furniture, your car and anything that is under the affected tree.
To top that off, the honeydew develops a black mold (no, now don’t panic, not the toxic black mold discussed in home improvement shows). This is just a black mold called sooty mold. It has a very ashen, dark black appearance.
That is usually the first time the homeowner notices there is a problem, long after the magnolia scale has taken up real estate in your trees. People notice the sooty mold appearing on their decks, sidewalks and driveways. They think that is the primary problem. But it isn’t.
The sooty mold on leaves isn’t as damaging to the plants, although its presence does reduce the ability of the plant’s powerhouse — photosynthesis — to make more energy for the plant because of reduced access to sunlight. Sooty mold can be washed off of all of your hardscape and leaves usually with a strong spray of water. You may need to add a mild detergent if it has been there awhile before you discovered it.
As for controlling magnolia scale itself … well, that is in and of itself, another sticky situation. The most successful treatments when dealing with pest insects are to look at their lifecycle and find when they are most vulnerable. And treat then.
By doing this, you are not only getting the greatest bang for your buck, moneywise, but you will also have the greatest control, using the least amount of product. To illustrate this idea, let’s look at the tomato hornworm:
You know that jumbo hot dog-sized green caterpillar that can make fast work of defoliating a whole tomato plant overnight? Homeowners will tell me they went to the store to get “the spray” to control the hornworms. I tell them, at that large of size, it would be more effective to use the can itself to mash them hornworm for control (or hire a kid who has a love/hate relationship with bugs to find the hornworms and mash them). As it would take an inordinate amount of spray to kill a large hornworm.
So, treatment strategies focus more on getting them when they are young. The problem is all the immature scale insects are so very hard to see. So, we rely on general timing. This can be a good or bad thing, depending on what Mother Nature is throwing at us each year.
There is a science called phenology, the study of the lifecycles of plants and animals. Agriculture and horticulture have made use of this study of timing by coordinating certain plantings and treatments based on when something happens in nature. And it is usually right!
For example, often I have people ask me if it is true that for the best potato harvest, a gardener should plant potatoes on St. Patrick’s day? Clearly, not in our area. As our weather on March 17th most years is still quite cold and often snow-covered. And that isn’t even talking about our cold, wet Will County soils are too wet to work, and the seed potatoes would rot, long before they germinate.
But there is another pairing of timings that does work, plant potatoes the day the first dandelion blooms. Or plant tomatoes when you see chive flowers. These pairings are not about a date on the calendar, but the relationships of plants. If the soil has been warm enough for the soil that dandelions are growing and putting on flowers, the soil is the approximate correct temperature for potato sets.
This phenology is also useful in some insect control applications — particularly when it comes to scale insects. The University of Illinois Pest Management for the Home Landscape manual suggests that when the spring-blooming shrub bridal wreath spiraea is finishing its blooming, it is time to treat pines for pine needle scale, because that is when their crawlers are active.
Similarly, it is time to treat for the devastating euonymus scale, when the catalpa tree’s large white flowers are starting to bloom. And treat spruce bud scale when Queen Anne’s Lace is blooming.
But what about for the magnolia scale? There are two optimum treatment times: late summer into fall is when the magnolia crawlers are present. But also, since the crawlers are the stage that overwinters, a dormant treatment is recommended during the winter.
When it comes to treating scales, using a horticultural oil is a great option. First, as I discussed in another column recently, horticultural oils are physical smothering agents, not pesticides (nerve agents) so they cannot build up a resistance to oils. Always read and follow labelled instructions on anything you use on plants. It is a federal law.
There are also some insecticides that work, and some that don’t do as complete a job. Acephate (Orthene) applied as a spray or foliar drench is effective, but the neonicotinoids (imidacloprid) have not shown consistent results.