Dogwood pest

[Franco]

I bought some bareroot redtwig dogwoods and all was fine until they start exhibiting this disease/virus. Does anyone know what this is and how it can be treated?

[rainbowgardener]

When did you buy them/ how long have you had them? How long have they been showing spots? What has your weather been like?

Unfortunately, I'm afraid they may be infected with dogwood anthracnose. It is a fungal disease that has been decimating dogwoods in much of the country. Like other fungal diseases, it thrives in cool wet weather, but it can attack at any time.

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

"Leaf symptoms develop first in the lower crown and progress up the tree. Symptoms include tan spots that develop purple rims. Leaves may also have necrotic veins and leaf margins, and large necrotic blotches. In some cases shot holes appear. Premature abscision of leaves infected in the spring is characteristic of the disease on C. nuttallii. On both hosts, leaves that are entirely blighted do not abscise in the fall. Infections often progress down the petioles of blighted leaves into shoots, resulting in cankers."

Treatment is to keep the tree as healthy as possible, keep it in full sun where leaves can dry out quickly, never water the leaves, cut off and discard infected leaves.

https://www2.ca.uky.edu/agcollege/plantp ... OR-W-6.pdf

"If the tree is valuable enough, fungicide sprays may be warranted. The active ingredients chlorothalonil (e.g., Daconil 2787), benomyl, thiophanate-methyl (Cleary’s 3336), mancozeb (Fore, Manzate 200), or propiconazole (Banner) are effective protectant fungicides. Fungicides should be applied beginning at bud break in the spring and continued
biweekly until hot, dry summer weather. Thorough coverage is essential. Without proper spray equipment, protection from anthracnose with fungicides will not be effective. "

Note the word protectant. That means it works better to prevent infection than to treat established infection.

The effective fungicides are environmental bad actors that ordinarily I would not recommend. In this case it may be a choice between those or letting dogwoods go the way of chestnuts, dutch elms, and now ash trees (emerald ash borer).

But read more and talk to people, be sure it really is the anthracnose. If so, you will have to figure out if your baby dogwoods that are already infected are worth taking extreme (and perhaps ineffective) measures to try to save.

[Franco]

Here you are once again with a thoughtful and helpful response.

I have thoroughly read both articles you linked, both of which and among others led me to also believe it's anthracnose.

I bought them off ebay maybe around March, but definitely sometime before summer. I'm in north east NJ and we had some really wet spells earlier on this summer and spring. They are in smaller pots so they dry out quickly, and I also wet their leaves when I water them with the hose. However, I didn't think conditions were extreme enough to make them vulnerable, although I seemed to have a ton of problems with fungal diseases this year so I could be wrong about the severity of the weather. My roses got wrecked by pear slugs, and I treated them with a fungicide and they were doing fine for a couple months, but after a few days of rain it looks like a new fungus has found them.

I don't know the exact names of the fungicides I have, I think I may still have Fungonil (or something like that). Are nursery-available fungicides the "extreme" measures you mentioned? Or is there a step up from regular homeowner pest management chemicals?

Thanks again.

[rainbowgardener]

"The most effective fungicides for control are the protective fungicide chlorothalonil (e.g., Ortho Max Garden Disease Control), copper sprays (e.g. Bordeaux mixture), propiconazole (e.g. Banner Maxx), and the systemic fungicide thiophanate-methyl (e.g., Cleary’s 3336, which is available for professional use only)
https://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7420.html

but the idea of the systemic is for big trees that can't easily be thoroughly sprayed. The systemic circulates through the trees system and thus is present in every leaf. But your baby trees are easy to spray thoroughly and can be readily sprayed monthly until cool weather. On an environmental soundness basis, I wouldn't recommend any of this stuff (except maybe the copper based stuff, which does qualify as organic). But the systemic is the worst.

Like I said, after that it is just a value judgment, what you are willing to do to try to save your baby dogwoods.

[Franco]

I'll take this into consideration. Thanks.