Hello Ernie,

Thank you for writing. You seem very well informed on the fungus attacking your vinca vine.

When I researched phoma stem blight on vinca, I did notice a few things: The fungus grows best early in the spring when the new stems appear and touch the infected soil. The fungus grows most readily in cool wet weather when temperatures are between 50 and 65 degrees. This year temperatures were optimal through March and April. March was fairly dry but April had a couple of large rainfalls when temperatures were prime for fungal growth. After about April 25^th, the temperatures were too warm for the fungus. (I used Waterford weather history as a rough estimate for Oakland County. Results may vary a little bit based on your exact location.) I would say that the effect of phoma stopped spreading, not due to applying fungicides, but because the conditions were no longer favorable for fungal growth. Another source states that fungicides need to be applied every 7 to 10 days during the favorable period of fungal growth. https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/cankers/vinca-stem-canker Three applications of a fungicide starting at the end of May probably do little good.

Another excellent reference is https://www.purduelandscapereport.org/article/phoma-stem-blight-of-vinca/

Also, you say the service applies imidacloprid. At MSU we favor Integrated Pest Management that targets treatments only when necessary. Imidacloprid is an insecticide and if you have not confirmed insects damaging the vinca, it Is a superfluous application of chemicals.

Vinca establishes deep root systems which help it be an effective ground cover under dense tree canopies. I would not necessarily be concerned about watering it, but if that appears to help, you should be able to water safely now, as the temperatures are way too warm for phoma to grow. Of course, to be on the safe side, it would be best to water early in the day so that the leaves and stems are dry through the overnight hours.

Finally, phoma is long lived in soil and is a killer of vinca vine. If the damage continues to thin your vinca vine stand, you may want to start considering a different ground cover, such as pachysandra.

Hello Ernie,

MSU does not have any specifically published research/treatment regimens for phoma on vinca minor. All I can do is read the same articles you have read, and I cannot offer any opinion about the effectiveness or ineffectiveness of the treatment. As you have obviously done considerable research I can only offer the following advice: Any search you do, trust .edu and .gov sources, because they offer research based suggestions.

I would also offer this advice. Phoma lives in the vinca tissues and the soil. As soon as a healthy stem touches the ground, it will be infected and ultimately die. You should clean out all infected and dead plant material from the bed. The attached article even suggests cutting back the entire bed and thoroughly cleaning out the plant material and allowing complete new growth to develop during warm, dry weather. However, even after doing this, the soil will still contain the fungus and the deeply grown vinca root material still may harbor the fungus. https://ask2.extension.org/kb/faq.php?id=835573

You can try the fungicide treatments you read about, but you are not likely to eradicate the fungus. Please see the statement in this article from Purdue saying that the fungus will survive for several years in the soil. https://www.purduelandscapereport.org/article/phoma-stem-blight-of-vinca/#:~:text=Given%20how%20long%20the%20fungus,death%20of%20newly%20installed%20plants.

One outbreak in cool, wet weather can reestablish all the fungal material you manage to kill off with your high maintenance treatment scheme.

You may also want to email the MSU Diagnostics group with your questions and pictures and see if they have a different opinion concerning your remediation plan. Email <personal data hidden>

I would still suggest that the best solution may be to consider a different ground cover plant.