Disease/insect On several ornamental plants

Question: I have what looks like the same disease or insect on several plants. They started on my fall blooming camellias last year, which are three years old. I sprayed them with horticultural oil throughout the summer and they seemed better but now they look like they’re dying. The same thing Seems to be happening to my jasmine, my photinia and a very large spring blooming camellia. A separate question involves crape myrtle bark scale. I had a very small infestation last summer. The trees were treated professionally in the fall and again last month. There are still small remnants. Is this something that I need to treat for regularly?

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied April 12, 2024, 4:16 PM EDT
response: We don't see any insects on the first photo sample of camellia leaves. The scattered pockmarks on the undersides of the leaf are not due to insect damage and are not an infection that will cause the plant any damage, so they can be ignored. If you see other indications of suspected insect damage, or insects themselves, please feel free to send additional photos. Cottony Camellia Scale tends to be one of the only insects of concern on camellia shrubs; you can learn what to look for on the linked page.  If camellia plants are struggling to do well, it may be related to growing conditions instead, such as roots staying too wet or the plant growing in soil that is not acidic enough. (Is it near a roof downspout outlet that puts extra water into the root zone? Is the plant near lawn that has lime applied every couple of years, or close to a building whose foundation might be leaching into the soil, raising the pH?) Horticultural oil might suppress a mite outbreak, if they were present and causing damage, but otherwise it should not be needed and won't be of much use for suppressing other insects. (It can help with scale, but only at certain times of year when the scale insects are most vulnerable.) Spraying horticultural oil in summer can risk leaf damage if it is applied in hot weather.  Can you send us a photo of the entire camellia shrub so we can see its symptoms? We can't see what kind of plant is pictured in the third photo, or what symptoms are being shown, because it's not in focus.  We don't see jasmine samples in any of the photos. Are you able to send us pictures of what appears to be bothering the plant? Very few jasmine plants are winter-hardy in Maryland; most are indoor plants.   The second picture of Photinia leaves appears to show a very common leaf spot disease that this shrub almost always seems to contract in our region, though it can be worse in years with wet weather. It is an eyesore, but doesn't necessarily kill the plant, though recurring bouts of heavy infection can cause leaf drop and weaken the shrub. Only a fungicide labeled for suppression of this disease (Entomosporium fungus), applied preventatively and repeatedly through much of the growing season, can reduce infection. It would have to be redone every year, so that degree of management and expense usually makes Photinia not worth growing in our opinion.  Crapemyrtle Bark Scale will be an ongoing problem if present in the area and infestations can take a while to successfully control. Plus, since crawlers (the juvenile stage that moves from plant to plant on the wind or via bird or squirrel fur/feet) can recolonize the plant at any time in the future, periodic monitoring needs to continue for the life of the plant. Given how abundantly this non-native tree/shrub is planted in Maryland gardens, this scale will probably be an issue well into the future.  How often a treatment is used depends on the chemical applied. You mention that the plant was treated professionally twice so far; did the company/applicator give you information on what they used? Some applications may need to be made several times per year whereas others might last a year or more per application. Systemic insecticides, which are absorbed into the plant's tissues, tend to last longer, but also might carry a risk of contaminating the plant's next set of flowers (nectar/pollen), potentially putting pollinators at risk. Another factor to keep in mind is that dead scale won't necessarily fall off the plant right away, so a treatment might be working to kill the insects, but it won't necessarily be obvious for some time, since the white waxy/fluffy material the insects generate could stay stuck on the bark until it finally weathers away.  Miri

responder: The Question Asker Replied April 12, 2024, 5:17 PM EDT
response: Hi Miri,Thank you for the quick reply. I’ve attached a photo of the entire camellia shrub and of the tops of the leaves. None of the other possible factors is present, so it may be the soil pH. I apologize. The jasmine is actually Carolina jessamine. I had so many people thell me they’re the same I started to believe it. They’ve done very well and are covered with flowers. The second and third photos are of one the tendrils.I agree that the photinia may have to go.I’ll have to ask the arborist what was used on the crape myrtles. It’s not on the invoice. The info you gave about scale was very useful.Thank you again,AmandaOn Apr 12, 2024, at 4:16 PM, Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied April 12, 2024, 6:11 PM EDT
response: Hello Amanda,  Thank you for the new photos. The camellia foliage color suggests either general stress (perhaps root zone, like competition with the aggressive groundcovers or moisture level or pH). However, it's not uncommon for camellias exposed to winter sunshine (if they are shaded by trees in summer) to cause leaf color fading. Is this shrub receiving several hours of summer sun, or is it shaded during the midday/afternoon hours once any overhead trees leaf-out? If they get too much sun, sometimes camellia foliage becomes yellower, though in that situation there's still often another factor at work.  The ringed patches are suspect and we will show them to our plant pathologist early next week and let you know what he thinks. Our initial impression is that they are caused by a virus, and if so, plant viruses are incurable, though not always fatal to a plant. When a plant contracted a viral infection can be difficult to determine, though insect feeding as well as tools contaminated with sap from another infected plant can be typical routes of transmission.  The spots on the Jessamine foliage don't look concerning, and as a semi-evergreen plant (one which keeps at least some leaves in winter), some degree of leaf degradation by the end of winter is typical on a variety of evergreens. We'd expect they will either shed later in spring, once new foliage emerges, or they may hang on for a while but will be more covered-up by new growth.  If you wish to test the soil pH, we suggest having it done by a soil testing lab since home test kits are more difficult to use and may produce inaccurate results. We can help to interpret the lab results if desired.  Miri

responder: The Question Asker Replied April 17, 2024, 7:02 PM EDT
response: Hi Miri,I’ll be very interested to know what the pathologist says. The camellias are shaded in the afternoon when the leaves come out on the trees. I have ordered a soil test kit from one go the labs on the list.Thank you,AmandaOn Apr 12, 2024, at 6:11 PM, Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied April 18, 2024, 10:13 AM EDT
response: Hi Amanda,  He took a look and thinks it does look viral; Camellias can contract several different kinds of plant viruses. (By itself, this is not unusual and doesn't mean they are unsuitable for growing in our area.) Not all will kill a plant, and for now at least, these symptoms look minor since very few leaves are exhibiting those ringed markings. You could pluck those leaves off if they are an eyesore, but plant viruses are systemic enough that other asymptomatic plant tissues will carry the virus, so pruning cannot eliminate it and there is no treatment. You can either replace the plant or wait and see if it recovers from whatever other conditions are causing the stressed off-color (too yellow) appearance.  Miri

responder: The Question Asker Replied April 28, 2024, 4:14 PM EDT
response: Thank you so much Miri. I appreciate your sleuthing.On Apr 18, 2024, at 10:13 AM, Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied April 29, 2024, 11:35 AM EDT
response: You're welcome!