What you are seeing there are the two most common issues that we see in plantings of cherry laurel.
The white that you are seeing is a type of sucking insect called scale. White Prunicola Scale is the one that infests Cherry Laurel.
Here is our page on it: 
https://extension.umd.edu/resource/white-prunicola-scale Check out the blog post linked at the bottom of the page too. You will want to prune out any dead branches and follow the management suggestions on the pages.

The holes in leaves are a more minor issue caused by a disease aptly called Cherry Shothole Disease:
https://extension.umd.edu/resource/cherry-shot-hole-disease
The amount of disease symptoms can vary from  year to year based on the weather, but the problem is primarily cosmetic and is not lethal to an otherwise healthy plant.


Christine

You're welcome.

The product pictured is a combination spray of an insecticide (the active ingredient tau-fluvalinate) and a fungicide (tebuconazole).

Tau-fluvalinate belongs to a chemical class called pyrethroids (synthetic versions of a chemical derived from certain chrysanthemums). Pyrethroids are designed to take longer to break down in the environment, which potentially makes them riskier to use when trying to avoid harm to beneficial or otherwise-harmless insects, because any contact with the spray residues could kill them. Pyrethroids are also a contact-kill insecticide (in contrast with a systemic, which pests must ingest as they feed), and since scale insects are protected from most topical sprays by their waxy shell-like cover, this is not expected to provide good suppression since the chemical won't really contact their bodies. (The fact that scale are not featured on the "insects and mites controlled" list further suggests this will not work well on them.)

Systemic (plant-absorbed) insecticides generally work best for situations like this since the scale will feed on treated tissues (sap or cell juices) and die some time after ingestion, and treatment does not rely on thorough contact with all plant surfaces to reach hard-to-access scale insects; since all of them are going to feed, they will all eventually be exposed to the toxin. Systemics do risk entering nectar and pollen too, which is why the timing of their application, plus the selection of an active ingredient in that group should focus on those persisting in the plant for the shortest amount of time, in order to avoid harm to pollinators visiting treated plants in bloom. Cherrylaurel blooms in spring, though heavily-trimmed plants don't bloom much at all, so this can be taken into consideration if you treat with a systemic.

It should be noted, though, that many commonly-available systemic ingredients (those in the neonicotinoid chemical class) are not legal for Marylanders to apply outdoors, so a certified pesticide applicator needs to be hired if they are to be used. Insect growth regulators [IGRs], one of the contact-type options mentioned in the scale management information, is another alternative, but they are generally not available "over the counter" and would best be applied by an experienced pesticide applicator who knows when to apply them based on scale life cycle timing. The crawler period for any scale species can only be estimated because it is highly weather-dependent. Details, when they are known, about the timing of crawler hatch for any scale species are included in its management information. We are currently past the degree-day benchmark for the egg hatch of the second generation. The third generation hatch would be expected around September or so.

Horticultural oil is a topical contact spray option, but since it doesn't work as well (it can help dissolve some of the scale wax to smother them, but isn't foolproof and needs excellent coverage of the infested bark to work well), it alone may not be enough to fully suppress a high scale population. Even using more than one insecticide, good control might take a year or more to achieve.

The fungicide component of the product is not necessarily going to be effective on Cherry Shot Hole, especially since that leaf disease is sometimes caused by a bacterium, not a fungus, which very few fungicides can affect. Shot hole is not serious with regards to Cherrylaurel long-term health and we typically do not recommend treatment. (Even high-quality wholesale nurseries growing thousands of Cherrylaurel for sale to garden centers have a hard time eliminating this disease.) One key way to reduce the likelihood of high infection or repeat infection is to avoid wetting the leaves, if you irrigate using a sprinkler or hose spray. If this is unavoidable, water early enough in the day so that foliage can dry by nightfall, since prolonged leaf wetness is more conducive to spore infection. Granted, you can't do anything about rain or dew, but keeping plants not pruned very densely and in a site with decent air circulation (not too close to a wall or corner in a fence, for example) will help speed leaf drying. Fungicides are preventative measures only -- they cannot cure existing infection, and they tend to need to be used repeatedly, with several applications per year, to suppress infection. Spores infect leaves well in advance of symptom development, so by the time you see damage, it may be too late to treat unless a re-infection cycle continues into the summer.

We do not keep track of the ever-changing list of chemical products (or their exact ingredients, which manufacturers sometimes adjust, as has happened with some Bayer products since neonicotinoid chemicals were regulated by some areas). We also don't recommend specific brand names or products except in rare cases (very specific herbicides, sometimes). If a web page of ours don't list a particular active ingredient to look for when managing a given disease, then that pathogen may not be well-controlled by widely-available fungicides. If you wish to avoid insecticide use or find the prospect of treatment (and hiring someone to do it) too costly, it may be more cost-effective or practical to just replace the plants instead. Depending on how large these are, new plants might have largely caught-up in size by the time the treatment program is complete. If these are grown in a row of all the same plant, consider mixing species if plants are being replaced so a pest or disease is less likely to spread through the entire group.

Miri

You're welcome!

It is probably too late for that second generation since its crawlers would have settled by now. (Once "settled," the crawlers start producing the wax shells that cover their bodies, so are much less vulnerable to topical sprays like horticultural oil.) Plus, it's hot enough now that timing sprays so they are less likely to injure foliage (should be below 85 degrees) might be challenging. Even though you'll only need to spray the bark, since that's where these scale live, some spray will inevitably contact foliage.

The third generation is expected to hatch around 3238 degree days [DD] or so. The most recent issue of the IPM report (produced by UMD Extension and geared to a commercial audience of nurseries and landscapers) shows the DD tally in Gaithersburg on Aug. 9 at 2325 DD. Take data points with a grain of salt because DD measurements can vary from town to town, from one part of a single yard to another, and even from one part of a plant to another. (Of course, those finer-level differences will be more minor than at city or county scale.)

You can use an online DD model like this one generated by Oregon State University (and others). The IPM report that we produce uses this model for its DD reporting.

• Use the following information to calculate GDD for your site:
  • Select your location from the map (or the pin closest to you)
  • Model Category: All models (default)
  • Select Model: Degree-day calculator (should be the default choice)
  • Thresholds in: Fahrenheit °F
    • Lower: 50
    • Upper: 95
  • Calculation type: simple average/growing DDs (again, likely the default selection)
  • Start: Jan 1
  • End date fine to leave as Dec 31, and you don't need to change any other selections.
  • hit the "click here to calculate/run" button
• On the results list, the "CUMDD" column is the running tally of cumulative DD on that date, so just scroll down to the current date to see the DD total thus far. Data below that point will be forecast DD based on the past decade.

That data points provided by the model will be close enough to let you know when to start looking for crawlers. If you have a magnifying glass, that will help you detect the crawlers because they will be very small. Spraying right around the time crawlers are emerging (or expected to emerge) will help knock the population down, though probably can't kill them all. Remember that dead scale don't always fall off the plant right away, so a treatment regime may be working but won't necessarily look like it's accomplishing much just yet. In either case, a handful of repeat applications will probably be needed; follow label directions regarding spray intervals.

Miri

Thanks! 

 

You're welcome!

Thanks for all this useful info.  According to https://extension.umd.edu/resource/white-prunicola-scale, the first generation of prunicola scale is after – 513 degree days (During the peak flowering of tulip poplar (Liriodendron tulipifera) and green hawthorn (Crataegus viridis ‘Winter King’) and the 2^nd is

after 1637 degree days.

 

Would you please tell me when would be the next good days on the calendar to apply horticultural oil?

 

Thanks.

 

 

Hi Steve, 

Horticultural Oil is more about the temperature outside but you are correct in wanting to know the degree days for applying for the crawler emergence. 

You want to make sure you apply the oil in the temperature range that it states on the label or it could burn the leaves (it should be fine on the bark though). 

In Howard County we are in the upper 300's for degree day. Tulip Poplars and Hawthorns are blooming mostly but it isn't a perfect timing, more of an estimation. With the days of higher temperatures recently, it has spiked quickly and today is supposed to be rather warm as well. Over the next few days we should be reaching the 500 degree day mark so maybe wait a week or so into mid-May. If you have a hand lens or magnifying glass you can try to look for the crawlers, but they are so tiny. They will be pinkish/salmon colored and may be in clusters which will make it easier to spot. 

Emily

Thanks. 

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