DYING VINCA MINOR/PERIWINKLE
I have a large bed of periwinkle that is dying. Started early last Fall. 1st a 3-4ft diameter circle would turn yellow. 2nd the center of the circle would brown off. 3rd the circle would enlarge t0 5-6ft. Very little of a 20' x 50' remains healthy and fully green. This bed was started 25 yrs ago and slowly expanded. Has always been healthy and attractive until last Sept. I suspect? a fungus brought on by all of last year's rain.
Please send us photos of the vinca minor so we can see what you are dealing with. Also, let us know what the site conditions are - sun versus shade, etc.
Some possibilities of the decline of your vinca may be phomopsis blight, a fungal disease, or voles. You did not mention the site that they are growing in. Vinca grows best in light shade in moist, well drained soil. If located in too much sun they will be stressed.
Stressed plants in full sun are more prone to infection and dieback. Also, old fallen leaves and debris can contribute to this. Has the bed been cleaned out and thinned recently to increase air circulation? See our website for more information. http://extension.umd.edu/hgic/phomopsis-and-phoma-dieback-vinca-groundcover
Also, look around the base of the plants for silver dollar sized holes. If you see these holes, you may be dealing with voles, a type of meadow mouse. They feed on the roots of herbaceous plants, trees, and shrubs and cause dieback. Voles use the groundcover to hide in. See our website for more information http://extension.umd.edu/hgic/voles-groundcovers