I've read with interest the many forum posts that claim vinca is almost indestructible. But here I am asking why its leaves are turning brown in patches and dying off. The leaves turn crispy brown in areas about 18 inches in diameter, and within 3 days there is nothing but a bare spot. I'm in zone 7 (Alabama). Temperatures have been in the 90's for several weeks, but there has been sufficient rain. I water when we go more than 5 days without rain.

For the past week (even though I see no signs of fungus), I've sprayed with a fungicide because I don't know what else to do. The remaining vinca looks very green and healthy although it hasn't had the purple flowers this summer like in years past. It's planted in a natural area under trees with about 3-4 hours sunlight per day.

Any help/suggestions would be appreciated.

I think the vinca needs more water on those hot days. True, vinca is practically impossible to kill but without sufficient water they will die.

I'd water every other day when it's in the 90's and water in the evenings so the vinca can soak up the water and utilize it best during the hot day ahead.

HI, 2.5 years later saw this Q :) Have recently been doing vinca gardening and your post was interesting because I have a similar situation in my farm too. I have some lovely blooming vincas and suddenly I have these bald patches of dried up vincas. I think the issue is of over-watering and/or watering from the above. I am going to check my dead plants to see if they have brown spots that are indicative of fungal infections (just read that on the internet today).

Another nursery guy told me that vinca varieties are annuals and perennials. But I am going to be hopeful and be careful of watering and pray the beauties are back in action!

I must apologize that I never posted my results in the forum. I took my dying samples to a plant pathologist who diagnosed it as a fungal disease called Southern blight. This is a common plant disease in Southern states. He recommended Bayer Disease Control for Roses, Flowers & Shrubs Concentrate(active ingredient Tebuconazole.) It worked and the vinca gradually came back, but the plants and surrounding soil must be treated with the product every 4 weeks during hot summer months. It gets quite expensive as I have a large area to treat. And I should clarify that this is "vinca minor," a ground cover also known as periwinkle. It is not the same as the vinca flower which is an annual and must be planted every year. I hope this helps someone else down the road.

http://www.bayeradvanced.com/product/Disease-Control-Roses-Flowers-Shrubs/concentrate.html