Help! Trying to identify disease on our dogwood

[ohmygarden]

After a harsh winter two years ago, our dogwood hasn't been doing well. This summer, it looks like it's developed a disease. There are spots on the leaves as well as foamy white blob-like growths on the twigs. Some large branches in the centre have completely died as well... I will post the images and hopefully someone will recognize what's happening and advise on what we need to do to prevent it getting worse: I don't want to cut it down, or start pruning before understanding what it has, for fear of doing more damage and/or spreading disease (if not specific to the dogwood) to nearby plants/trees.

Thanks in advance for all who try and help!

[rainbowgardener]

The foamy stuff is spittle bugs, but they generally do very little damage to plants. The bug hides under all that foam, to protect itself. They do suck some of the sap from the plant, but rarely enough to harm the plant – unless there are huge numbers of them. So I don't think they are causing the rest.

I don't know for sure, but I think your disease may be anthracnose, which is wiping out dogwoods across the country.

You didn't tell us where you are located. That is always important, because there is hardly any garden question which can be discussed without regard to location and climate.

Are you in one of the drought struck areas? Drought stress is one of the things that weakens trees and makes them more vulnerable to infections like this. On the other hand, it is a fungal infection and like other fungal infections, thrives in cool, wet/humid conditions.

If it is anthracnose, the spots start with tan centers and purple margins and progress to leaf die back as you showed.
https://www.extension.purdue.edu/extmedia/bp/bp-48.html

Here's another article about dogwood anthracnose:

https://www.na.fs.fed.us/spfo/pubs/howto ... ht_dog.htm

As far as control, it says

"Dogwoods receiving good cultural care will be better able to withstand anthracnose during years in which the disease is favored by weather conditions. Maintain the health of dogwoods by watering during periods of drought. Mulching trees can help to reduce watering needs as well as protect trunks from mechanical injury. Avoid overhead watering to minimize the chance for leaf infections. Improve air circulation around trees to help dry foliage and reduce infection.

Effective control is possible only if the disease is detected before extensive dieback occurs. Prune and dispose of diseased twigs and branches to reduce potential sources of inoculum and improve tree appearance. Raking up fallen leaves may be of some benefit. Remove succulent branches*as they form to prevent trunk canker formation. Avoid high nitrogen fertilizers which stimulate succulent branching. Trees with poor vigor may be bolstered by applying a balanced fertilizer in early spring."

*aka "suckers"

But yes, one of the things that is very bad about the anthracnose is that unlike some diseases, it is not very specific and will infect sycamore, white oak, elm, and maple as well as dogwoods.

You can send a sample to your local agricultural extension office for diagnosis and consultation about what to do.

[ohmygarden]

Thanks, rainbow!

I will research both and see what I can do. I suspected anthracnose because of the purple spotting, but was completely thrown off by the spittle bugs.

[rainbowgardener]

you jumped in while I was still editing.... where are you located?

[ohmygarden]

Sorry about that! We're in Southern ontario - durham region. We do get very humid weather during the summer...

After the ice-storm two years ago, a lot of plants suffered and didn't do well last year. The dogwood seemed fine, and didn't start doing poorly (noticeably poorly) until now. I hope I'm not too late...

Thanks so much for your post. It is so helpful.

[GardeningCook]

Is that a variegated regular nursery dogwood or a variegated Kousa dogwood? Both are normally somewhat resistant to anthracnose if grown under good to optimum conditions. It's the native Dogwood that normally succumbs to the disease.

One thing I noticed immediately from the photos is that your dogwood seems to be suffering from serious crowding & competition from other plants. This could very well be the source of your problem. Good air circulation is paramount to healthy tree growth - even when normally lower-canopy trees like dogwoods are involved. They like a LOT of air circulation which it doesn't look like yours is getting. Add in humidity, & you're hanging out the welcome sign for all sorts of fungal & bacterial diseases. Not to mention the Spittlebugs, which aren't normally interested in Dogwoods, or any trees for that matter.

[ohmygarden]

hmm, interesting. It's actually on it's own... the pictures are a close-up, but all of the same tree... But thanks for the update. I'll keep that in mind and avoid planting anything around it.

I'm not sure about what kind it is.. we call them silver-leaf dogwoods (they have red branches)

[GardeningCook]

hmm, interesting. It's actually on it's own... the pictures are a close-up, but all of the same tree... But thanks for the update. I'll keep that in mind and avoid planting anything around it.

I'm not sure about what kind it is.. we call them silver-leaf dogwoods (they have red branches)

Ahhh - that makes all the difference in the world! "Silver-leaf Dogwood" is a red-twig dogwood shrub & not the same as the dogwood trees I (& others) were thinking of. Red-twig dogwoods are not only shrubs rather than trees, but are also far more susceptible to anthracnose & other diseases & pests. It explains the presence of Spittlebugs, which one won't find on Dogwood trees. One good point is that anthracnose (if that IS what you have, but which I'm starting to doubt) tends to cause cosmetic damage only, unless it increases year to year to the point where it starts weakening the plant. A much stronger possibility now that you've provided plant I.d. is that you have "Redosier Dogwood Canker", which is a disease fairly specific to Red-twig dogwoods & causes the dieback you're seeing. Do a websearch on it & view the pics.

I would still try to increase air circulation around the plant though, as that really does help keep diseases at bay.