Hello,

Thank you for reaching out to Ask Extension with your questions. 

It looks like you have some variegated Dogwood shrubs, perhaps the Ivory Halo variety,Cornus Alba 'Bail Halo'.

• Did your "Picture This" app tell you what fungus you have by chance? 
• Can you also tell me which copper fungicide product you are using? 

Most fungi that can cause leaf spotting are host specific. Also, most fungiide products are specific as to which fungi they will attack and on which host plants. Without knowing what product you are using, and for what type of fungus, I can not tell you if you are using the correct fungicide. You can look on your product label to see if Dogwood is listed or not. The timing of fungicide treatments is also very important. There are certain windows when fungicides will be effective, and the rest of the year they do nothing (but can cause possible harm). It is imperative that you know what fungus you have, so that you know the disease cycle and correct timing of chemical controls. Fungicides can also cause phytoxicity in plants, which can look a lot like the damage you are seeing, so always make sure to read the product label and apply only as directed to help avoid injury to your plants.

• When did you first notice this damage? 
• Have the brown spots worsened since you used the copper fungicide product?

The most common type of fungus you would see in Colorado is Powdery Mildew, which is not evident in your picture. Other types of fungal problems would have noticable symptoms, such as a yellow or purple halo (or border) around the damaged necrotic tissue, which I also do not see when zooming in on your picture. I can see what looks like distorted and possibly curled leaves hiding below the upper leaves. Anthracnose can cause this type of damage. Most fungi that cause Anthracnose are host-specific and cause variable symptoms. In Colorado, we typically see this in some of our trees, like Oak and Sycamores. Here is more information about Anthracnose:

https://ipm.ucanr.edu/home-and-landscape/anthracnose/pest-notes/#gsc.tab=0

https://planttalk.colostate.edu/topics/trees-shrubs-vines/1766-oak-anthracnose/

If you would like to find out whether or not your plant has a fungal, bacterial or viral disease, your best bet will be to take a sample to the Colorado State Plant Diagnostic Lab for a positive ID. Here is more information about this lab:              https://agsci.colostate.edu/agbio/plantclinic/ 

As for the leaves and removing them, if you removed all the leaves with the brown spots, then you won't have much of a shrub left. Removing leaves that are completely dead and brown would be okay, but leaves with healthy green are still photosynthesizing and creating energy to the plant. Proper sanitation in the fall will be very important. Removal of all leaf debris will be necessary to not over winter any diseases by leaving the leaf debris in the landscape. 

One final thought, or question for you.

• How are these shrubs watered, for how long and for how often?

Pests and disease tend to attack already stressed plants. Make sure that you are giving enough water to your plants so that they are not water stressed, even through the winter months. A lot of times, drought stressed plants can have curled and distorted new growth in spring, when coming out of a dry winter. If you do not water your landscape during our dry winters, you should consider doing so. Here is more information:

https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/

I hope this helps,

Dawn

Hello, I would agree that you probably don't need potassium. While the various apps that identify plants and plant problems can be useful, they are often not correct with the plant ID's and/or with the diagnosis of plant problems. Using them as a starting point can be helpful, but always check that what your app is telling you is correct. I think the most beneficial thing would be to properly monitor your moisture. Mosisture meters are realtively cheap ($10) and can help you get an isea of the soil moisture throughout your yard and around this plant. Remember that over watering can be as bad as under watering. Drip can often clog, so make sure you check it often and remember to water through winter also. https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/ Thanks, Dawn