by Ed Bradley
No, the sky is not falling, but scale is coming. Some rosarians were recently surprised to find scale in their gardens (including me!). It could be very wide spread, so please consider this as a "scale alert" and examine your rose bushes very carefully. If you don't have it, there is a pretty good chance that you will. So, keep a lookout...
Until a couple of years ago, to my knowledge, we had not heard of nor seen, scale on roses. Then, some of our expert growers found it. Thinking that we had gotten away clean, I didn't worry about it this year. However, when I began the Fall cut-back, I discovered it. Panic time! I immediately called a couple of expert CRs, Jackie Clark and Eddie Garcia to find out what they had done in 2001 when they had it. I then called Linda Rawe (Horticulturist) and Nathan Riggs (Entomologist), both with the County Extension Service, both of whom had spoken to our Club recently. I found severe infestations on some bushes, moderate on some, while most seem to be clean. Where it comes from remains a mystery, and I'm sure each of us has an opinion. However, as I learned in my early years of problem-solving - when you find yourself in a hole, it is counter productive to worry about, or spend time analyzing how you got in the hole. The real question is "How do I get out?" So, let's take a look at what can be done when you find scale.
How do I recognize scale? Scales are almost microscopic, but can be seen with the naked eye. Scales will be tiny grayish, or brown spots on your rose canes, with heavy infestations from the older, lower canes to fewer scales on the newer stems at the top of your bush. They will tend to congregate around major joints, such as where you made your major pruning cuts back in the Spring. They may also encircle thorns, at the base. In extreme cases, they may completely cover the stem, and appear as "grayish bark" on the stem. Scraping with a fingernail, however, will reveal that is not bark, but scales. Other than eyesight, symptoms will be a yellowing of leaves, then the color of the cane may progressively turn yellow, to brown, to black. (It's dead!)
To effectively eradicate the scale, we need to understand the physiology of the pest. There are many kinds of scale, and they seem to love a huge variety of plants, from vegetables to shrubs, to trees. We are dealing with the "oyster shell scale", so named because its hard shell under magnification looks like an oyster shell. Under the shell is a soft-bodied insect. During the early life-cycle stage, the insect does not have the shell and is referred to as a crawler because during this life phase, it crawls and moves about on the host plant. At the conclusion of that life phase, it will find a "feeding spot" on the plant (on roses, it is usually a stem). It will stop crawling and insert its mouth parts through the outer tissue and into the vascular tubes, or xylem, which transport moisture and plant nutrients. As they extract nutrients from the stem, their excretion forms the hard shell which serves as their armor against predator insects as well as insecticides.
How do I get rid of scale? The two principal means of getting rid of these little "suckers" are to use an oil-based spray, or a systemic insecticide. The oil-based spray will coat the shell and literally suffocate the varmint. The systemic insecticides will be absorbed into the plant tissue, transported along with the moisture and plant nutrients, and will kill the little critter when it is extracted from the plant tissue and ingested.
To my surprise, I found a plethora of "cures" available on the market. The user can select those that best fit their situation, cultural practices, and pocketbook.
First, there is a variety of oils, but a word of caution about their use. There are dormant oils to be used when the plant is dormant. There are summer oils, all-season oils, ultra-fine oils and oil emulsions. Read the label carefully. All of the oils should be used only when the air temperature is between 45 - 85 degrees. When it is too hot or too cold, the oil will cause a defoliation of your rose bush. Oil based sprays found in local garden centers Include:
Secondly, there are several effective systemics; however, it takes days or weeks for them to do the job. If oils cannot be used because of temperatures, the best approach with systemics would be to use a systemic spray which may act quickly, and a granular systemic applied to the soil, which will be taken up through the roots to the upper plant. (You can see why this process may take 2-3 weeks or longer.) Available systemics include:
Di-Syston, by Hi Yield. This is an affordable granular pesticide which is applied to the soil. It kills lots of pests other than scale. I was told that Di-Syston is now a "restricted" chemical, so when the shelf stock is depleted, it will be available only to licensed applicators.
In addition, there are a few organic solutions you may want to try:
I'm sure there are other remedies. Look around and ask questions of qualified specialists or full-service nurseries. The main concern is to carefully examine your rose bushes. If you find scale, load up your arsenal with the weapons of choice, and attack!